Welcome to buses! I got interested in buses a while back and found the world far more complicated than I had imagined. I was very happy to have people help me learn stuff. This document is my attempt to summarize what I have learned so I can help other people have fun with fewer suprises than I had.
I undoubtedly have made mistakes and omissions, and there is probably information that is there but poorly organized and hard to find. If you find something here which seems wrong, it probably is. If you have questions, suggestions, corrections, or whatever, please drop me a note at <bus-0035@pardo.net>. Happy bus!
I expect most readers are in one of a few broad groups:
I am interested in all of those things, but I am not equally knowledgeable in these areas, and I am not very knowledgeable in any of these areas. So don't take my word for it --- think about whether it makes sense, talk with other folks, and so on. I do hope that despite errors I make, the information will be at least largely correct and will help you to understand the issues.
Some of the information here is of special interest to one category of reader and less interesting to another. Some of that is handled just by the organization, but some stuff is mixed in. For example, RV enthusiasts may want to know if there is room for a generator set, while seated enthusiasts probably are interested in storage decisions without need to know if it works for a generator set, and folks interested in transporation will be curious about how storage sizes and layout changed to reflect changes in how buses were used. So while some things are separated out, others are necessarily or accidentally mixed in. I don't know a better way to organize it, so please bear with me, and I hope to have an index at some point.
Finally, some people prefer the term ``coach'', but since I am including school buses and some other commercial passenger vehicles built on truck chasis, ``bus'' seems more appropriate in many places. This document does not distinguish between ``buses'' and ``coaches'', so please do not be upset if I call your pride and joy a ``bus''!
Buses as we know them today first appeared about 1900 and in some ways have changed substantially and in other ways have changed little. This brief history of buses is wildly incomplete but should serve as a good starting place for following discussions.
The term ``bus'' probably comes from ``omnibus'' meaning ``many things at once'' or ``for all''.
The first regular bus service was started in Paris in the 1660's. It's invention is credited to Blaise Pascal, a famous mathemetician and scientist. Buses were distinguished from taxis and other coaches because they ran on fixed routes, on a regular schedule, and with lower fares. The system was successful during it's year-long trial, but was abandoned on Pascal's death.
In about 1900, most public transit was horse-drawn cabs and coaches, horse- electric- or coal-powered rail vehicles, or water craft. As gasoline motors became practical, companies started using multi-passenger vehicles to provide transportation where rails and water transportation were not available. Buses became more and more popular in part because of their speed compared to horses and their flexibility compared to rail vehicles. They were also popular for their relatively low cost. High-volume rail service is cheaper to operate in the long term, but the starting cost of track and heavy-duty rail vehicles is too high to pay back on low-volume routes. Even where long-term payback is possible, the relatively low cost of entry in to the bus market is highly attractive. Roadways are built and maintained at public expense, while rails are largely built and maintained at private expense, so bus service avoids some costs through taxation ``sleight of hand''. Finally, in United States in the 1940's, companies selling buses, rubber and oil offered special deals to transportation companies to help get them as long-term customers, further reducing the cost of entry. Today (circa 2000), rail is returning and airplanes are by far the most popular way to travel long distance. However, buses maintain low cost of entry and route flexibility and they are a standard part of public transportation both within cities and between cities. Probably the biggest challenge to bus transportation today is relatively slow speed compared to cars.
The earliest buses were built by adpating other vehicles, for example by putting benches on a truck bed, or extending a car body to hold more passengers. As bus sales increased, buses were usually built with the body or body and frame made by a body builder and the mechanical components bought from other suppliers. As production volumes increased further, it became more common for high-volume buses to have most parts of a bus built all by one company, notably Ford, GMC and Mack. By about 1960, Ford and Mack exited the market and the U.S. government started antitrust investigations against GMC, and there was been a return in the U.S. to bus companies which build bodies and frames and purchase drivetrain and suspension items from other companies. In Europe, M.A.N., Mercedes and Volvo still build most parts of the bus.
Dates below are for entry in to production rather than demonstration or protoype, unless noted otherwise.
Early buses were stretched cars or truck frames with special bodies built by independent coachworks.There are as many ways to describe buses as there are ways to slice bread. Here are some broad categories. These categories are not preceise, because things always spill over categories and because different parts of the world have different needs.
Loosely, a ``bus'' is a motor-driven road vehicle for carrying many passengers and designed for commercial use several to many hours a day with an expected life in this kind of service of more than ten years. Many buses also carry some amount of freight, and several percent of buses are sold new without seats to be used as RVs, since the same many of the attributes which make them desirable for commercial service make them desirable for RV use.
A close cousin of the bus is called the ``trackless trolley'' or ``trolley coach''. It is an electric bus powered by overhead wires. These share almost all components with buses except the drivetrain, so this document typically includes them under the term ``bus'' except where drivetrain is concerned.
Buses entered the mainstream of transporation in the 1920's. Mechanically, buses have evolved slowly and continually. The bodies have gone through (roughly) four major eras:
[Low-roof, engine-forward] Early buses often used wood in their construction, were built on truck chassis, had low roofs --- making it necessary to stoop when walking inside, and sometimes had one door per row of passengers. These buses were built typically in the 1920's and early 1930's. |
[Old Look] Many buses built from the 1930's through the 1950's -- and some in the 1960's -- were built with one or two entrance doors and were tall enough to walk in standing upright. They were usually aluminum-bodied and many were all-aluminum construction. They were boxy with rounded corners, were fully painted, and were built with relatively small windows made of small pieces of rectangular pieces of flat glass. Transits typically had a higher second row of ``standee'' windows. Mechanically, old-look buses introduced rear-engine and transverse-engine designs, air conditioning in the 1930's, and in the 1940's, mid-engine buses and city buses with automatic transmissions, typically 2-speeds. |
[New Look] From the 1950's through the 1970's -- and some in the early 1980's -- many buses were made using much larger pieces of glass, with curved glass for the front and rear windows, and non-rectangular glass for the side windows. The large curved front windows on new-look transit buses gave them the nickname ``fishbowls''. Many buses were less boxy, with more pronounced features, and many buses were partly painted, with anodized aluminum showing through elsewhere. Bodies also got wider and longer -- up to 265cm (104") instead of the more common 245cm (96"), and a greater proportion of buses were 12m (40') instead of 10.5m (35'). Mechanically, ``new look'' buses also introduced air-bag springs instead of steel springs and power steering as an option. The new look era also saw the widespread use of ``stepped'' highway buses with a low floor in the front and high floor in the rear. |
[ADB] From the 1970's through today, some bus designs transitioned through a rounded design that was less space-efficient, then to a less-rouned boxy form that was more space efficient than the New-Look buses. Many buses switched to either polished stainless or fully-painted bodies, with some of them being fiber panels on a conventional, rather than monocoque, frame. Frames and sometimes bodies started to be made of stainless steel for corrosion resistance better than either plain steel or aluminum. Bodies continued to get larger -- 265cm (104in.) width beceame fairly standard in the U.S., and an lengs of 14m (45') became common for highway buses and articulated city buses of 18m (60') appeared and became common. Mechanically, city transit buses got many-speed transmissions that would carry them more readily to highway speeds, wheelchair lifts, and articulated transit buses became common. Highway buses got automatic transmissions -- in 1980, most highway buses sold in the USA had manual transmissions, by 1999, a survey of 6,000 buses showed that only 12 of them were delivered with manual transmissions ([missing link]). By 2000, new highway buses were often fitted with wheelchair lifts. |
Until the 1950's, most buses used leaf spring suspensions. Leaf springs are simple but have fairly high friction and give a harsh ride. In the 1950's, rubber-in-shear and airbag suspensions were introduced. All three systems are in widespread use today; see below for more details [link].
Early buses used mechanical, then hydraulic brakes. In the 1930's, air brakes were introduced on heavy buses. Hydraulic brakes are common today on lighter-duty buses; air on heavier units. In the 19??'s, anti-skid brakes were introduced. See below [link] for more about brakes.
Buses are heavy and can be difficult to steer at low speeds. Power steering was introduced for transit use in the 19XXs. Steering is easier at speed, so power steering was not widespread among highway buses until 19XX.
Early buses had limited interior lighting. Gradually, generator sizes increased and were then replaced by alternators. Increasing available electric power was used in part to drive more and brighter lamps. Then, transit incandescents were replaced by fluorescents, which dramatically increased the interior brightness. For transit buses, the front lamps are artificially dimmed to reduce glare for the driver.
Destination signs were originally simple placards. The desire to keep signs ordered led to the introduction of ``roll'' signs -- painted or printed cloth signs wrapped around and stretched between two spools; by rolling the spools, the appropriate destination could be displayed. Rolls were then driven by electric motors to allow rapid scrolling through many destinations. Next, electronic destination signs were introduced, allowing every bus in a fleet to carry all destinations and allowing moving or multipart displays for showing complex route information. Early electronic signs used a magnetized flap with color on one side and black on the other; an array of electromagnets flipped the flaps to show routes. More recent electronic signs use bright LEDs (light emitting diodes) for improved reliability.
Early transit buses were operated in cold weather with the assumption that passengers were dressed for the cold. Heating was minimal. Over time, interior heating systems have been improved.
Air conditioning was offered as a standard option starting with the 1936 Yellow Coach 743. Then, and for many years, the air conditioning was driving with a separate gasoline motor because the main motor was not powerful enough to drive both air conditioner and the bus. As more powerful V-configuration engines became available, it became standard to drive the air conditioning from the main engine; when the air conditioner load was low, the extra power was available to propel the bus.
This section is for enthusiasts who wish to own and operate a bus, either as a ``seated coach'', or as a motorhome conversion.
This section is also a useful introduction to many of the buse life-cycle issues which are discussed in detail later in the book. For example, imagine you run a small bus business and are considering purchase of another bus. There are many new and used units available, what should you get?
For most people, the first consideration is financial:
If you are terrifically rich, you might be purchasing a new unit. In that case most of the following does not apply. However, a new medium-duty bus with no interior costs well over US$100,000 and so that is not an option for most folks. In addition, there are tradeoffs between available new units, so some of the following does apply.
A used bus costs much less, but it costs less exactly because it has problems that make it less desirable to the transportation company, agency, department or individual that originally purchased it. For example:
Although many of these problems can be overcome by a private owner, they are not to be dismissed lightly:
Most of these issues can be overcome or worked around, but these issues do mean that it is highly important to use care when purchasing.
A heavy-duty bus will typically see 500 to 1,500 kilometers of service every day. That translates in to 3,000 to 10,000 kilometers per week, and 150,000 to 500,000 kilometers per year. Buses typically see ten years of regular service before being retired. Although buses are often out of service for repairs and are often rotated to light-duty routes, it is common for buses to go over 1,000,000km before the first owner sells them; and such buses are often sold in to continued light duty service before reaching a price an individual buyer can afford.
It is common for people to say ``I will not be driving it that much, so I do not need to worry about service.'' However, after millions of km of use, many parts are fatigued and can break in light use. Sometimes, even new parts can and do sometimes break in light service. For example, starting the engine, especially a cold one, causes some kinds of wear worse than running it. And, as many buyers find out, when a heavy-duty part breaks in light service, it can be very expensive to repair.
For example, a set of tires for an RV might be US$200 instead of US$2,000 for a bus. A rebuilt motor for an RV might be US$2,000 instead of US$10,000 for a bus. So while a bus may ``seem'' like it should last forever, it can actually be quite expensive to keep on the road. In the best case, everything lasts. But even a drivable bus may need substantial repairs to be roadworthy and reliable -- if you have to get new tires and fix the brakes, engine, transmission, and so on, you can easily spend several times the original purchase price and several times the cost of an adequate RV.
As a bus approaches retirement, it is common to save effort and costs by omitting normal periodic maintainance, replacement and repair beyond what is required for safe operation. Areas of reduced maintenance include:
Often, buses are sold either because something is wrong or because the bus is aging and the maintenance costs are beginning to rise. And, if a seller has several similar buses, the best parts may be swapped off the bus being sold in order to keep the others on the road. Thus, it is common for a bus to leave service needing repairs or having worn and tired items which will soon need repairs. Therefore, expect needed service and expenses in all areas. Common issues include:
In addition, it is rare for a vehicle to leave service and get sold immediately. Often, the seller is getting rid of it exactly because it is not in use. When any vehicle sits, various things go wrong. For example,
If the bus is already converted for motorhome operation, there are a large number of additional items which may need service, repair or replacement:
You should also consider what it will cost you to modify and own a bus. For example, many transit buses through the 1980's are unable to travel at highway speeds. Drivetrain changes for high-speed operation can easily run thousands of dollars, and hill-climbing may be slower as a result of those changes. Similarly, the normal service and repair costs on diesel engines are much higher than on gasoline engines. For commercial use, those costs are spread over hundreds of thousands of kilometers, but for a bus which is used only occasionally, the costs can be much higher per kilometer traveled. Normal wear-and-tear items to consider include
Note that the costs may vary widely with the age and make of the bus. It might seem, for example, like old parts should be cheap. And, indeed, there are some parts which have been used on trucks and buses for decades and which are available at junkyards all over. On the other hand, some parts may be difficult to find or easy to find but very expensive. For example, a used distributor cap for a 1950's Hall-Scott engine may cost about US$500 -- just for the cap. Although most parts are not so expensive, it may be hard to find or adapt parts for a bus that is 50 years old. Include the possible costs of parts when deliberating the cost of a bus, and shop around for parts suppliers before you leave on a trip, so there is less risk that a breakdown will strand you and your bus for weeks while you are finding parts.
Finally, many buses are sold ``as-is, where-is'' and may be non-running or otherwise non-drivable. Trucking or towing a bus often costs in the range of US$2/km. Since a non-operational bus will cost something to make it run, the added costs of moving it may make a cheap or free bus be a very poor bargain indeed.
That is all pretty scary. And it should be, because operating a bus can be a very expensive proposition. That said, many people buy and operate buses with modeset expense, and many others ultimately have large unexpected expenses but are prepared to deal with the problem and so have, overall, a good experience and the feeling their money has been well-spent.
The important lesson here is it can be very expensive, so make sure you do your homework to avoid or anticipate expenses, and so that if an overwhelming expense does occur, you can get rid of the bus before you run out of money, rather than after you run out.
A good rule of thumb when looking is: there will always be another bus that will do. Do not buy a bus because ``it might work out''. Instead, buy a bus because you are reasonably well-informed about what you want, what is generally available, and because you have thoroughly investigated the bus in question and it you have fair confidence that it can work out, and that if it does not work out you will be merely disappointed rather than broke.
If you want a motorhome, a bus that needs lots of work and then is not really suited to use as a motorhome is no bargain, even if it is free. Conversely, if you want to restore a vintage bus, there is no point in spending big money to get a ten-year-old bus in good shape.
If you want a bus, note that many states license buses based on gross vehicle weight, and that can be over US$2,000 per year. In addition, insurance for a commercial vehichle can be quite high. If you are considering an older bus, check vintage vehicle registration in your area. Although it may restrict you to (say) less than 5,000 kilometers per year, the reduction in registration and insurance fees can be tremendous. Similarly, some areas allow private buses to be licensed as cars. Any time a bus is licensed for non-commerical use, it must never be used commercially, and, typically, it must also not be used to transport passengers.
Whether your goal is motorhome, seated, or something else, you should also consider what level of quality will make you happy. Some people are happy with frequent breakdowns as long as they are never too costly and as long as the vehicle is safe. Other people are looking for a bus which repsents the best in its class, with no visible or hidden blemishes, no breakdowns, and so on. You should be honest with yourself about what you want so that you get a bus which you are fundamentally happy to own, or you will be happy with the decision to not get a bus because the combination of model, quality, and price you demand are not currently available..
Another consideration is what will you be happy driving? For example, some folks will want a shorter and narrower bus, while others are willing to drive something larger. The smaller bus will be easier to drive and park and is allowed more places, but a smaller vehicle has less inside space and less storage space. In addition, specific makes and models of buses are only be available in specific sizes.
Storage is an issue, too. Crica 2000, one yard said that 10m spaces were US$60/month and available at the time I called; 11m spaces were US$70/month and had a several-month waiting period, 12m spaces were US$80/month and were a yet longer wait, and 13m spaces were US$90/month and were probably unavailable until the next year. Best if you have your own space! Parking while traveling can be similarly constraining. For example, many camp grounds have a 10m maximum length, municipalities often limit parking of long or tall vehicles, and some roads have vehicle length limits.
Driving a vehicle which is clearly expensive can be a benefit while traveling on the road. For example, some travelers do unpleasant things like dump feces in the street (I have seen it), panhandle or steal; and poorly-maintained vehicles are more likely to have breakdowns that become a hassle for individuals or the community. Many areas have laws that regulate whether you can sleep overnight in your vehicle; how long you can park in one place; and so on. If you appear ``undesirable'', you may be unwelcome, may be harassed, or may be subject to stricter enforcement of those laws -- either because the police are being extra-careful or because residents call to complain. If you have a bus which is obviously well-maintained, it shows you have money and helps community members feel at ease.
Conversely, if you have a super-expensive vehicle, you may be harassed or targeted for theft while traveling through poorer areas. This is probably less of a problem, but still a consideration.
There are many types of buses. Aside from age and condition, some common issues, especially for mothorhome conversion, are:
The condition of the basic bus ... how much work are you willing to do just to get it on the road, safe, and sufficiently reliable? You can hire out any work you will not or cannot do, but often at great cost. Best to become familiar with rates before you buy.
How much work to make it ready for your intended use? Conversion is a time-consuming process, with many hidden detours such as insulation, plumbing and wiring; working around the existing bus layout and limits; fitting stuff to the inside; etc. Similarly, authentic restoration often requires a great deal of tracking down parts. Thus, the more you need to change or repair, the more you care about details of the final result, and the higher the quality of fitting you require, the greater the time and/or cost.
To summarize: there are no ``right'' answers, but think a lot about what you want, go look at what is available (including looking at a few in person!), and then re-think what you want based on the realities of what is available.
Here are a few more things to think about:
There is always a tradeoff between complexity and ease-of-use. The simpler system is typically cheaper and more reliable; but the complex system may require less effort, less time in service, or may be easier --- less distracting --- to use. A complex system is also necessarily less durable: doubling the number of parts requires that each part is four times as reliable in order to achieve the same level of reliability as the simpler system.
Similarly, there is always a ``packing'' problem: the goal of a bus is to get as many people and as much cargo from A to B, but in a reasonable time and with reasonable comfort. Tighter packing can increase the revenue per trip, but may also require more expensive construction or compromises in operating efficiency, service, and so on.
Finally, buses have only a finite service life: parts break, buses are in accidents, and the rules of operation change. In addition, both private and government operators benefit greatly from a lower initial bus price. Thus, while durability is a big goal, there gets to be a point where improved durability comes at a high enough price that buyers would rather buy cheaper and less durable buses and replace and repair them more often.
This section discusses some features of buses with an eye towards issues such as complexity, efficiency, cost.
Early buses used a simple mechanical linkage to the motor mounted in front of or next to the driver. When rear-engine buses appeared, they continued to use a mechanical linkage, typically a long wire or cable.
Cables stretch. Mechanical parts need lubrication and wear nonetheless. Wear and forgotten lubrication makes the pedal hard to push and leads to stronger return spring, which makes the pedal yet harder to push. Getting a straight run to run a cable the length of the bus can be difficult. The linkage needs to be immune to small motor motions that occur as the motor moves under load, or the movement may change the throttle. And so on.
For these reasons, many newer buses use an air throttle. The pedal is an air valve, like an air brake. The motor has a diphragm like a small version of a brake pot. An air line runs from pedal to motor.
Diesel buses fitted with air throttles are also often fitted with a ``throttle delay'' mechanism. The throttle delay allows the throttle to open only slowly. When you push gently on the pedal, the throttle opens precisely. When you push hard --- open the throttle suddenly --- the throttle delay limits the rate at which the throttle opens. Driving with a throttle delay is most noticible leaving a stop: you press hard on the accellerator and the engine revs up only slowly. Most other times the delay is not significant because you are changing the throttle slowly or changing it suddenly but only a small amount; and because you feel less seat-of-the-pants ``kick'' when underway than you do (or don't) when leaving a stop.
The throttle delay exists for several reasons. First, opening the throttle suddenly can cause diesel engines to smoke a lot, which is annoying to people at the curb, and which also produces a lot of air pollutin. A throttle delay reduces this problem. Second, the problem is particularly noticible with turbocharged diesels, because the maximum fuel that can burn depends in part on the speed the turbocharger is spinning. At low speeds, the governor may inject too much fuel, making the smoke problem extremely bad. When the engine smokes a lot, it is also dumping more waste in to the oil, which is bad for the engine life. A throttle delay brings up the engine speed and turbocharger speed together, reducing the amount of smoking.
Some regions have a throttle ``snap test'' in which an idling diesel engine is suddenly set to full throttle and the emissions are measured. Typically, the goal is to measure opacity. It may be measured using instrumentation, or officers may somteimes do it by eye and issue a ``get it checked out''. The basic idea is that at normal operating temperatures, black smoke indicates too much fuel and not enough air; if the problem is bad enough to show on sudden accelleration then it is both occuring commonly (accelleration is common) and may be a problem other times but not so noticible.
Early buses used mechanical brakes, where linkages ran from the driver to the wheel. As you might imagine, getting high leverage was important to be able to stop, but at the same time it was important to have minimum slop and stretch in the linkage so that the driver's energy was not all used up before it got to the brakes.
Hydraulic brakes perform the same function as mechanical brakes, but the oil in the system can go directly to the wheels with very little slop or stretch. Hydraulic brakes appeared in cars the early 1920's (attributed to Malcolm Lougheed, who changed his name later to Lockheed). Hydraulics are improvement over mechanicals because hydraulics lose less energy between driver and brake. They also have disadvantages: hydraulics can leak; and when hot, the fluid can boil. Good hydraulic fluids also tend to absorb water, so brake lines are prone to rust.
Power assist is a further improvement because the driver does not need to supply all the energy needed to stop the vehicle. The idea of power assist is that the says what to do, and the assist amplifies the driver's instructions. Power assist first appeared in passenger cars in 1928. One disadvantage is that if the power source goes away --- for example, the engine stalls --- then the brakes suddenly get much worse. Thus, power brakes typically have a power resivoir that helps with at least a few brake applications after power goes away.
Air brakes also perform the same function as mechanical brakes, and work in much the same way as hydraulics but use air instead of hydraulic fluid. Air brakes first appeared in trains; George Westinghouse invented them in 1868. Car air brakes first appeared on the 1903 Tincher. Air brakes have the advantage that strong brakes can be controlled using a simple valve. In addition, no special fluid is reqired, so trailer brakes can be connected and disconnected easily.
Although air brakes are similar to hydraulics, there are a few key differences. One difference is that hydraulic brakes push directly on the shoes, while air brakes run at lower pressures and so the air pushes on a lever that moves a cam to apply the brakes. The extra linkage is a source of some maintainance problems and failures compared to the direct application of hydraulics. A second difference is that hydraulic fluid sits in the hydraulic system all the time, whereas air must be pumped (compressed) in to the air system. As a result, the hydraulic system still works if power goes away, though it may work worse with the power assist gone. However, when power goes away from an air system, the compressor stops pumping air in and the brakes stop working entirely. Although air brakes are equipped with a compressed air resivoir, the brakes stop working entirely soon after the compressor stops working.
A third difference is that the driver must learn a special set of procedures for using air brakes. The driver typically has both an air pressure gague and a warning drop flag [image] or buzzer to indicate low air. The driver must wait for air pressure to build before it is safe to move the bus. On loss of air pressure, the warning will drop or sound and the driver must be prepared to react before the brakes stop working. Many regions require special licensing for commercial operation of air-braked vehicles. The license requirements include knowledge of a daily air brake inspection and testing procedure.
Early air-braked buses used a separate mechanical brake for parking and emergencies. The most common arrangement is a brake mounted on the transmissions and activated by a long lever next to the driver. The transmission brake has the advantage of leverage through the differential (typically 2:1 to 4:1 leverage) and the long hand lever gives both a long travel and good leverage. Such brakes are typically called ``Johnson Bar'' brakes, I do not know why.
Two disadvantages of the manual parking/emergency brake are (a) it does not self-apply if the air pressure drops; and (b) strong application depends on the operator pulling hard. Thus, buses after about 1965 are typically equipped with a brake which self-applies if pressure drops too far, and which can be applied with an on/off switch for parking. The two major types are ``spring'' brakes and ``DD3'' brakes. From the driver's perspective they are similar; see [link] for mechanical differences. Automatic brakes are typically used only on the rear wheels, so if air pressure suddenly drops, the front wheels can be used to steer even though the rear wheels are likely skidding. Automatic brakes also require that air pressure builds up to release the brakes before the vehicle can be moved.
Most buses with manual transmissions --- all except the [Mack clutchless] --- have a clutch pedal. As with the accelerator and brake, there is a desire for simplicity, but the simplest clutch may be difficult to operate.
Clutch force was a relatively minor problem with older buses, because the engines were relatively small --- often around 150 KW. However, greater engine torque requires stronger springs to keep the clutch engaged, and modern buses often have engines with twice the torque of the older engines. As a result, disengaging the clutch can take a lot of strength. And while bus engines may be smaller than many car engines, bus engines often produce their power at low RPMs and high torque compared to a car engine, so torque may be four times that of a car engine with similar total horsepower.
The simplest clutch mechanism is a mechanical link from pedal to clutch. As with an accelerator pedal, wear, forgotten lubrication, the labor of remembered lubrication, getting a straight run for the linkage, and so on are all issues. An additional issue is that manual transmissions are difficult to shift when stopped, so it is common to sit at a light with the clutch depressed. That can lead to a tired leg in a hurry.
For these reasons, some buses are equipped with a hydraulic, assisted, or powered clutch. A hydraulic clutch still uses just the driver's power to operate the clutch, but a hydraulic mechanism may have less slop and stretch than a mechanical linkage. On heavy-duty buses, the most common aid is an assisted clutch: when the driver pushes on the clutch, an air cylinder helps out. Some buses have an air clutch, where the clutch pedal is like an air brake or air throttle pedal, and air pressure runs a diaphragm at the clutch. An air clutch has the disadvantage that it does not work until there is air pressure.
For reasons I do not understand, all are fairly rare, even though drivers frequently complain of fatigue from operating the clutch on heavy-duty buses --- a problem which is made more severe by the relative rarity of synchromesh on manual-transmission buses.
A gear shift seems like a simple item, but there are several ``suprising'' gear shift arrangements on buses.
Buses from the 1940's through the 1970's often used buses where reverse is selected by a reverse switch. From neutral, activate the reverse switch and move the shift lever to a position which is normally a specific forward gear, and the bus is now in reverse. Sometimes, the reverse switch is on the gear shift lever [[image Flxible Visicoach]]. Other times, the switch is somewhere on the instrument panel [[image GMC1, GMC2]].
Some buses select a low-low gear or select between speeds on a multi-speed differential or transfer case using a switch.
Even though many buses use just a few forward speeds, the shift pattern may be odd. For example, [[image Flxible Visicoach]] uses an ``H'' pattern. The usual starting gear on flat terrain is 2nd gear, with low-low first and reverse selected by solenoids. Note that the fourth gear is unlike car transmissions. This pattern is used for the convenience of the transmission builder, but leads to confusion when a single operator uses several types of buses in one fleet.
2 R 5 | | +------+ | | 1 3 4
Most buses place the shift lever on the floor so that the shift linkage can go as directly as possible back, along the floor line, to the transmission. A direct path minimizes slop and stretch.
The GMC PD-3751 ``Silversides'' (1948-??) is probably the only bus with a manual transmission shifted from the steering column. Drivinng a Silversides reputed to be especially difficult because the shift lever has a rather rubbery connection to the transmission.
Turn the steering wheel, steer the bus. Simple, right?
Buses are heavy, which makes it hard to turn the steering wheel. Buses use large steering wheels for better leverage, but if there is too much leverage, your hands have to move very fast for normal steering.
In addition, the long wheelbase of buses means you need to turn the wheels sharper than a car to take the same corner.
The faster you go, the easier it is to turn the steering wheel, but at low speeds it can be quite tiring.
Transit buses spend a lot of time at low speeds, and pulling in and out of bus stops. Some routes are on winding streets, and some routes may be over an hour from end to end, with little or no break if traffic has been heavy. Thus, driving in transit service can be quite taxing. As the joke goes, ``Power steering by Armstrong.''
Transit buses were often equipped with power steering as early as the 1950's, shortly after it was offered for cars, and before it was common on school or highway buses. Some buses use air-assist power steering; it is rumored to be helpful, but far short of ``power'' steering. With hydraulic power steering, many transit buses use smaller-diameter steering wheels and/or quicker ratios, reducing the driver effort to get in and out of bus stops.
Instruments tell a driver key things: Is the bus working right? Is the bus moving at a safe speed? Is the bus moving at a legal speed?
For example, buses with air brakes need enough air pressure to work the brakes, so an air gague and an low air pressure signal tell the driver if things are working right. Similarly, it is common to have a temperature guage or signal: bus engines work hard, and can be damaged if run hot. Oil pressure and battery charging instruments are also common.
The speedometer helps with safety and in legal driving. Many roadways are marked with safe speeds. The safe speed may depend on visibility, curves, hills, road conditions, and so on. For example, bus brakes can overheat easily going down hills, so signs will give safe speeds for heavy vehicles. Similarly, maximum speed may be governed by law for non-safety reasons, such as noise, uniformity of traffic flow, and so.
Some older buses use the tachometer to indicate both engine speed and road speed. The tachometer is marked with several bands, one per gear, indicating road speed based on the engine speed and known ratios between engine and road speed.
Using the tachometer this way is simple, cheap, and reliable. Unfortunately, it also requires more of the drivers attention, since the tachometer is complicated and thus more difficult to read [[image]]; and because the driver must remember or discover the current gear in order to determine the proper part to read. Such complications are unfortunate for at least two reasons. First, they are error-prone, so the driver may get the wrong number due to a slight error. Second, they distract the driver from paying attention to road hazards. There are also mechanical complications: changing any of tire size, differential ratio, or transmission renders the speedometer markings incorrect; and, an such markings are impractical with an automatic transmission.
Strip-of-indicators in Flxible transits [[image]].
Visibility vs. driver position [[image: RTS speedometer]].
Driver controls are more complex than in cars because there are many more things to control. [[images of some driver control areas: 743, GM, Flxible clipper/transit, ...; describe]]
E.g., on/off day/night on GMC transits
Transit buses have door controls [[images; describe]].
Highway buses --- external release
Modern key switch
Buses are built in several styles: with engines at the front under a separate hood, in the front, next to the driver, in the middle under the floor, and at the rear. Engine placement is a suprisingly comlicated issue.
Let us work backwards from the wheels. It is simplest to transmit power to wheels which do not steer. Rear-wheel steering is unstable, so the front wheels are steered. As a result, all large buses, and most other buses, are rear-wheel drive.
Buses of the 1920's and early 1930's typically placed the engine at the front of the bus out in front of the main body. This is known as a ``conventional'' layout. Conventional placement gives easy motor access, separates passengers from engine noise, and gives plenty of space to lay out a simple drivetrain. In addition, many parts can be shared with truck designs, which helps to reduce the bus purchase price. However, there are several disadvantages. The space in front is ``wasted'' since it does not carry passengers or cargo. It may be tricky to fit the engine, suspension, and steered front wheels in to the same space, leading to design compromises. Heavy engines are over the front wheels, which tends to overload the wheels, but steering pairs of wheels is difficult [link]. Finally, the forward engine must go to the back axle, making it more difficult to build a low-floor bus. For light-duty buses, the advantages
Starting in the 1930's, some buses were made with the engine in front, and with the passenger compartment built around it. [[diagram]] This ``cab forward'' layout allows the bus to seat more passengers. However, the motor housing usually intrudes in to the passenger compartment [[picture]], and the motor is still in front so cab-forward does not solve the other problems of a ``conventional'' layout. The engine also intrudes into the passenger compartment, reducing some of the potential space benefits, while increasing the amount of heat and noise in the passenger compartment.
From the 1930's to the 1990's, some mid-engine buses were built with the engine under the floor, between the front and rear axles. Mid-engine designs use a flat or ``pancake'' design so the engine does not intrude in to the passenger compartment. The mid-engine design can thus seat many passengers. The engine does not overlap the front axle, reducing steering/suspension compromises. The engine weight is shared with the rear axle, reducing the front axle loading. There are at least two major drawbacks to the mid-engine design: a mid-mounted engine is difficult to service, and and the mid-mounted engine interferes with under-floor storage and low-floor designs. Examples of mid-engine designs include some ACF-Brill, Crown, and White buses.
Also starting in the mid 1930's, buses were built with the motor mounted behind the rear axle. This is the dominant design for heavy-duty buses today. A rear engine puts the engine weight on the rear axle. Since the rear wheels do not steer, it is convenient to use dual wheels or even multiple axles to support the weight. A rear engine counter-balances over the rear axle and thus removes weight from the front axle [[diagram]]. A rear engine also intrudes little in to the passenger compartment and allows larger under-floor baggage bays, or low-floor construction. A rear engine is relatively easy to service compared to a mid engine. It is also relatively easy to isolate drivetrain heat and noise from the passenger compartment.
Probably the biggest problem with rear engines is that the engine, transmission, and differential must all fit in a short space. Thus large engines and multi-speed transmissions are difficult to fit. Even where the bus design allows a large rear overhang, the power train must still be short: placing the engine too far aft may remove too much weight from the front axle, making the bus unstable [[diagram]].
How crowded is it in a rear-engine bus? Consider, for example, the length from the rear axle to the rear of the bus. A Yellow Coach 743 is [[distance]] from the center of the axle to the back bumper. The engine is [[length]], the clutch is [[length]], and the differential is [[length]] from the center of the axle to the U-joint yoke. In addition, the bus requires a telescoping driveshaft, so the axle can go up and down relative to the bus body. For 15cm of travel, the minimum driveshaft length is about 30cm. The overall length of engine plus clutch, plus driveshaft, plus differential is [[length]] --- which is longer than the back of the bus! Clearly some innovative packing is needed to make it all fit!
[[A rear engine is near the drive wheels, reducing frame and drivetrain windup.]]
The simplest design places the engine, transmission, and drive shaft all directly behind the differential. This layout is called ``T-drive''. [[Diagram.]]
[[Example: Flxible. Note engine length, axle-bumper, ...]]
T-drive has the advantage that it uses standardized parts. However, in the 1930's heavy-duty engines were all inline engines. That made the drivetrain too long to fit in buses with a short rear overhang. In addition, inline engines are relatively tall, so they bulged in to the passenger area. These problems grew worse with increasing engine sizes.
Some buses worked around these problem by placing a baggage compartment at the rear of the bus. Thus, the engine only crowded the baggage space. Examples of this type include the some Becks, the Flxible Clipper and its successors, and medium-duty GMC highway buses such as the GMC PGA-3301. Other designs ``annexed'' the rear of the bus. Although there was no engine bulge in the passenger area, the last 1-2m of the bus also held not passengers or luggage. Examples of this type include the GMC PD-3302 [link PBM ODT #1945].
In the late 1950's, V-6 and V-8 engines were developed which were neither as long or as tall as inline engines. At the same time, bus floors were relatively high, especially for inter-city busses with large baggage bays. Thse changes made it practical to build heavy-duty T-drive buses.
T-drive is arguably a better engineering choice than V-drive. However, V-drive was the most common configuration for transit buses well in to the 1980s. At any given time, transit properties would have many ``prior-generation'' V-drive buses in service, and staying with V-drive simplified inventory and training. V-drive finally started waning because [[?? GM was forced to leave the transit business? Because fuel economy demanded better T-drive transmissions? ...?]].
One limit to overall drivetrain size is the driveshaft must be a minimum length. Some buses use a ``drop box'' which allows the driveshaft to to the forward side of the differential, and then gears ``drop'' the power to the differential input. The drop box moves the driveshaft mount point about 20cm [[??]] forward. Examples include Flxible VL-100 and MCI [[XX]].
Disadvantages of the drop box include increased unsprung weight, complexity, nonstandard parts, more friction, and more to break. Historically, VL-100 drop boxes came loose. Solution: remove studs and replace with high-grade bolts, make 'em tight.
One way to get a large engine at the back of the bus is to turn it ``sideways'' so it is parallel to the rear axle. Bevel gears turn the power 90 degrees and send it forward to the differential, where more bevel gears drive the axle. This arrangement allows a short rear overhang and uses a conventional rear axle.
A disadvantage of the system is that motor space is still constrained. Mack designs such as the 1934 CQ model centered the differential. Thus, the engine could be no more than half the width of the bus ([Mack Arch], pg. 71). Since engines are raltively heavy, side-to-side balance may have been hurt by the offset engine. Ford offset the differential on the axle, which allowed a slightly longer power pack. However, there is relatively little space between the rear wheels, especially with wide brake drums, so the gains were only modest.
Since the motor width is constrained, it is not convenient to mount the fan, radiator, and other accessories with the engine. Instead, extra machinery is required to mount them on the other side of the bus.
Another disadvantage is that the drive power goes through two sets of 90-degree bevel gears, and bevel gears are less efficient than gears between parallel shafts.
The Mack CQ and CM also use a non-standard transmission, The Ford uses a standard transmission, but doing so constrains the engine size.
[[Diagram of Mack and Ford transmissions.]]
The V-drive is like a 90-degree drive where the engine is so wide that both ends of the motor are behind rear wheels. Instead of sending the drive shaft straight forward, the drive shaft exits the transmission at an angle and enters the differential at an angle. This angle layout is called V-drive. [[Diagram. Show both rotations.]] V-drive was patented by Dwight Austin of Pickwick; he was subsequently hired by Yellow Coach and the first V-drive appeared in 1934 as the Yellow Coach model 718, type 41.
Compared to a 90-degree drive, V-drive allows a longer engine, better side-to-side weight balance, and simpler mechanical layout. Driveline efficiency may be slightly better: although drive goes through angle gears, the angle is not as steep as a 90-degree arrangement. The driveshaft is also slightly longer, allowing it to operate with less vibration at the extremes of suspension travel.
Disadvantages of this design include the need for both a special transmission and a special differential. The system is sensitive to driveline angle, including offset and mismatched angles [[diagram.]] For example, a 19XX GMC [[???]] uses an [[XX]]-degree driveshaft, while most newer GMC buses use an [[YY]]-degree driveshaft. Thus, it is not possible to switch only the power pack or only the rear differential. (As an added complication, the rear axle of the [[???]] is not bolt-compatible with newer axles, so it is not even easy to replace all components as a unit.)
RJ Long says (paraphrase) 4104 ring & pinion pumpkin offset to driver's side of axle centerline. 4106 ring & pinion pumpkin offset to curb side. (Viewed from above lookingforward from the engine compartment.) Dunno about angle, etc.
An ``accidental'' disadvantage of the V-drive layout is that GMC buses fitted with Detroit Diesel motors put the transmission on the right, which requires the engine to rotate in the opposite direction from normal. Detroit Diesels are easy to reverse (by changing the camshaft), but there is often a large cost difference between V-drive bus engines and otherwise identical engines with normal rotation. Mack used a V-drive with a normal-rotation engine, for example on CM and CO bus models ([Mack Arch], pg. 74), but GMC, the largest volume maker of buses, set the standard. Curiously, some small GMC buses, such as the TGH-3102, used a conventional-rotation engine and the transmission on the left, thus introducing inconsistencies in the product line.
The V-drive layout was important when inline engines were common. When shorter V-configuration engines became available, it was possible to use T-drive, but many transit properties have continued to specify V-drive configuration simply because they already have a shop full of V-drive equipment, and mixing units would mean duplicate spares and varying maintainance and repair procedures.
Another choice is to use an integrated motor, transmission and differential. A transaxle arrangement is short because the differential is rigid with the rest of the power pack and the driveshaft is eliminated. Instead, there are axle shafts leading from the differential to each wheel. A disadvantage of the transaxle is that it requires a non-standard rear axle, and the rear axle must clear the area where the differential is located so it cannot be a simple axle through the centers of the wheels.
Transaxle layout is used widely, for example, on older Tatra, Porsche, and VW cars. A transaxle layout was used in the Yellow Coach model 700 type 40, which may also have been the first rear engine production bus. Yellow Coach soon switched to V-drive; I do not know of any other buses to use a transaxle layout, nor do I know why it is unpopular. I do note the engine compartment did intrude in to the passenger compartment ([YC Arc], pg 42), but it is not clear the intrusion was any more than the pushed-forward seats required by a similarly-tall transverse engine. It is also possible that a laid-over ``pancake'' engine would have fit well.
Remove need to co-locate engine, transmission, differential. Used widely since the 1930's for locomotives, but in buses historically expensive, inefficient, and heavy. Even modern electric-drive systems use a few ranges of straight-through gearing for highest efficiency.
The longer the bus, the larger rear overhang can be tolerated, because there the forward weight has more leverage to counter-balance the overhung engine weight. When rear-engine designs appeared in the 1930's, most buses were 10m (30ft.) and under. Today (circa 2000), most rear-engine buses are 12m (35ft.) and over.
Consider, for example, the AC Transit cut-down Dial-A-Ride buses which were reduced from about 12m to about 10m by removing a window section and the associated bodywork. The bus was fitted with a concrete-filled ballast tank near the front axle to keep enough weight on the front wheels that the bus would handle well.
Allison V-drive automatic transmissions were used widely in buses from 1947 to 1990. There were probably between 70,000 and 100,000 Allison V-drive automatic transmissions made, spanning many models. This section provides a brief introduction and overview.
| Model | Speeds | Features & Notes |
|---|---|---|
| VH | 2 | Introduced 1947 |
| VS1-8 | 2 | |
| VS2-6 | 3 | For DD 6v71-class engine; 0.80:1 highest ratio |
| VS2-8.1 | 3 | For DD 8v71-class engine; 0.60:1 highest ratio |
| VS2-8.2 | 3 | For DD 8v71-class engine; 0.72:1 highest ratio |
| V730 | 3 | 0.85:1; introduced 1979. |
| V731 | 3 |
There are five VH versions: VH4, VH5, VH6, VH7, VH9.
There are three VS2 versions: the VS2-6; and two VS2-8. Detaled info is in the Allison Service Manual (SA 1239G) on the VH and VS transmissions.
In each of the VS2 transmissions, there is a bevel gear ratio and a splitter ratio. The ``splitter'' is a planetary gear set that is on the input shaft. It provides the overdrive function. The overall ratio is the overall ratio from the input shaft to the output shaft in top gear.
In all VS models, the torque converter ratio is 3.75:1 at stall. ``Stall'' is when power is on but the wheels are not turning. The torque converter ratio is typically only important at low speeds, since once you are moving at normal road speeds you have a geared connection.
The VS2-6 has a bevel gear ratio of 1.04:1. The splitter ratio is 0.69:1 and the highest overall ratio is 0.80:1. The highest ratio is obtained by multiplying the bevel gear ratio and the splitter ratio. This is the same ratio that the Spicer four speed had in the 4106. With the 4 1/8 (4.125:1) rear end, it normally gave a top speed of about 120 kph (75 mph).
The VS2-8 had two versions. Version 1 used a bevel gear ratio of 0.87:1 and a splitter ratio of 0.69: giving a highest overall ratio of 0.60:1. Version 2 used a bevel gear ratio of 1.04:1 and a splitter of 0.69:1, giving a highest ratio of 0.72:1.
A typical V730 had a 15% overdrive giving a 0.875:1 highest overall ratio. Some were built with different bevel gear ratios, giving a 1.04:1 overhall highest ratio. The lower-ratio units were mostly used with smaller (e.g, DD 6v71) engines and in steeper hills. By 1990 the sales brochure only showed the overdrive unit. See the assembly number found on the transmission nameplate. Look up the assembly number in the Allison parts manual, which will list it as an A or B group code. Group code A is the 0.875:1 ratio and group code B is the 1.04:1 ratio.
There were several changes to the V730 during its production run. For example, V730d reflects the fourth version.
The VS2 can be overhauled ``in frame'' whereas the V730 must be removed to the bench. One person reports his VS2 gave flawless service for over 80,000 km, and he bought it was used so did not know how many miles it had before he installed it in the bus. The V730 he installed was overhauled twice in 50,000 km --- at great cost.
Each transmission was manufactured with a ``data plate'' that often provides enough information that an Allison dealer can tell you how the transmission was originally built. Note that many parts are interchangeable between transmission models. Therefore, a transmission today may not match the original build.
There were various other sub-models of Allison V-drive automatic transmissions. There was an air-operated Allison(?). It used compressed air internally to shift. Later,there was a hydraulic shit version. The first hydraulic version was called a ``dip shift'' because the transmission would ``dip'' the engine speed while it was shifting to high, in order to avoid a jerk. Later, there was the ``power shift'' which could shift without needing to dip the engine.
See: ``Allison Automatic Transmission V700 series parts Bevel Gear Section Compiled by Gary Carter.''
There was a Spicer 2-speed. Some early Spicers were repudedly troublesome ([Mack Arch], pg. 92). Today, it is difficult to get parts for Spicer V-drive transmissions, and seals are a notable problem, though it may be possible to remanufacture other seals to fit (Coach Maintenance, 2002).
The driveshaft takes power from the transmission and delivers it to the differential. In nearly all buses, the transmission is mounted to the bus frame, while the differential is mounted ot the axle. Since the axle is sprung, it moves; the driveshaft must deliver power while the axle moves up and down. Also, when power is applied to the wheels, there is an oppositereaction force that tries to twist the axle. Although springs and links tend to resist the force, they are not perfectly stiff, and so the axle rotates some under load. Thus, the driveshaft must also allow for that misalignment. [[diagram]]
By far the most common kind of driveshaft is a splined telescoping unit with Cardan-style universal joints, also called ``U-joints''. The spline allows the driveshaft to both transmit drive torque and also get longer and shorter. When the spline is loaded, there is friction between the two parts of the driveshaft and it gets harder to make the drive shaft grow and shrink. Thus, hitting a bump with the power on can cause the drive shaft to pull on the U-joints and other drivetrain and suspension parts. It is thus vital to keep the driveshaft lubricated.
The U-joint allows angular misalignment between the two sides of the joint. If one side turns at a constant speed, the other side runs on average at the same speed, but it speeds up and slows down throughout each revolution. It is as if you were pressing and releasing the accelerator pedal twice for each revolution of the U-joint: on average you are pushing half-way on the throttle, but at any given moment you may be more or less than half-way. The speed may be said to ``flutter''. The larger the misalignment of the U-joint, the greater the flutter. [[Graph showing for input angle N, output is +/-.]]
If both ends of the drive shaft are misaligned by the same amount, then the first U-joint drives the driveshaft at a flutter, but the second one un-does the flutter. In effect, the second U-joint cancels the flutter of the first one. Although equal alignment should be smooth, in practice there is some vibration from constantly changing the speed of the driveshaft. Beware, also, that improper assembly can cause the driveshaft to double the flutter instead of canceling it.[[diagram]]
When the driveshaft ends are misaligned by different amounts, the speed variations do not cancel out. The motor and transmission are a large flywheel attempting to go a constant speed. Similarly, the bus is a heavy thing attempting to go a constant speed. However, the non-canceled flutter is constantly trying speed up and slow down the bus. The result is great vibration and high forces on the drivetrain, leading to quick wear.
For these reasons, drivetrain alignment is important. For simple parts replacement, things will probably be good. However, when installing a new power pack or axle, or when changing the suspension or typical bus loading, it may be necessary to examine the alignment. Note that a shorter driveshaft has to go through a more extreme angle when the axle moves, so alignment is more critical with short driveshafts. [[diagram]]
The usual goal is to have the output of the transmission in line with the differential when the bus is at its neutral or ``nominal'' loading so the axle is in the position it will be in most of the time when cruising down the road. Alignment means that the ends are in a straight line, but it also means that the shafts are in a straight line. [[diagram]]
V-drive is the same idea, it just happens the drive shaft runs at an angle. Note, though, that there is are extra things to consider in setting up a V-drive bus: the differential and transmission shafts can move side-to-side, just like on a T-drive bus, but making the transmission and differential closer or further apart also changes the alignment, which does not happen with T-drive. Also, all T-drive differentials and transmissions are 90deg, but V-drive differentials and transmission may have different angles. [[for example: ???]]. Although the alignment does not need to be perfect, it does need to be very close or the drivetrain will wear quickly.
A few old buses (c. 1920's and earlier) used chain drive. In these designs, the motor drove the sprockets mounted on the frame, and the sprockets drove a chain that in turn turned the rear wheels. The chain tension under load was opposed by an [[??]] arm with pivots at both sprockets.
Chain drive is relatively simple and rugged. It also mounts the differential on the bus, rather than the axle, improving ground clearance. The drive chain is exposed, increasing service needs and risk of contamination. Chain drives cannot be used with high-speed buses because high centrifugal forces limit peak chain speeds.
The differential takes power from the driveshaft and delivers it to the axles.
Differentials come in many ratios. The axle often has a tag saying the ratio. Example: RTS were built with ratios of 5-3/8, 5 1/8, 4 5/8 and 4 5/9. At least four other gearings fit: 5 6/7, 4 1/8, 4 1/9, and 4 1/10. All are hard to find used. 4 1/8 and 4 1/9 were maybe available in GMC Suburbans. 4 1/10 is available from Meritor at about $1600.00 just for the two gears. It is reputedly harder and more expensive to set up. The expense of rebuilding the carrier could be another $1000. 5 6/7 == 50 mph 4 5/8 (4 5/9) == 65 4 1/8, 4 1/9, and 4 1/10 == 72mph A complete gear set/carrier is sometimes called a chunk or pumpkin. Finding a high speed set is difficult because transit axles often use a 14 bolt carrier instead of the 12 bolt that goes in the parlor coaches. The 14 axles have a physically larger ring and pinion than the 12 bolt. I have found a 4 5/8 NOS at a bargain basement price of $200, and I cannot afford to not use it. If I change to slightly larger tires, I can nudge 70 MPH part of the time. BTW, the governor on my 6V92 TA is already turned up to 2200 RPM, and all the Detroit experts to whom I have spoken, say that at 2300 a 6V92 risks throwing a rod and self destruction. The only other issue is fuel economy, and at 2200 I get about 6.5 MPG. With the 4 5/8 I will still get only 6.5, because I will still be going flat out at 2200 on the highway. With a 4 1/10 I could back off to 65 or 70 at 2000 RPMs and get about 8 or 9 MPG. This would be nice, but it actually only saves about $40 per 1000 miles in fuel. So it is a trade-off I can live with. Some equipment codes athttp://www.angelfire.com/ca/TORONTO/VINcode.html Very useful!
It may be desirable to put newer equipment in an older bus. Some reasons include:
ACF Brill was the company formed when ACF, ``American Car and Foundry'' purchased J. G. Brill.
See the Pacific Bus Museum roster for a good summary of ACF Brill highway buses. ACF Brill also made transits.![[Vern Rainey's 1940's Beck]](./img//beck-seattle/img-0.250-P1010016-trim.jpg)
Built mostly heavy-duty school buses also built some highway buses. Mostly built mid-engine buses. It operated in the Los Angeles area of Southern California from the early 1900's to the early 1990's.
See the Buskid's web page for more on Crown.
Gillig made mostly school buses for a long time; currently (circa 2000) they produce transits almost exclusively. Manufacturing plant in Hayward, California.
See the Buskid's web page and Gillig's web page for more on Gillig.
In 1946, auto manufacturer Kaiser produced a prototype
63-passenger articulated highway bus that was all-aluminum
[Kaiser bus].
![[Kaiser Artic]](./img/clubs.hemmings.com/clubsites/pnwkfoci/history/1946/KaiserBus.jpg)
The GMC and TMC ``RTS'' model was one of the most distinctive-looking late-century ``ADB'' buses. It had wheelchair lifts and independent front suspension, and a rounded shape unlike other buses. Design features included:
Unfortunately it also had a large number of ``teething'' pains and a variety of design disadvantages compared to earlier buses, including
In addition to the above problems, GMC exited the bus business in [???], so the remaining models were all built by TMC, which was a Canadian subsidiary that was made a separate company when GMC exited the bus business. Although the TMC buses were built well, ordering from outside the U.S. was more complicated for some properties buying the buses.
Despite these problems, RTS buses were ordered in large numbers and many saw service lives over ten years. This was due to a variety of factors including
The original Scenicruiser design gave Greyound many problems. There were reports of metal buckling under the high passenger windows. The drivetrain used a pair of Detroit Diesel inline 4-cylinder diesel engines, connected to each other by a viscous coupling. The engines and fluid couplings were a source of problems and Greyound eventually sued GMC, who subsequently replaced the engines with newer V-8 diesel engines, which gave reliable service. However, the episode strained relationships between GMC and Greyhound, leading Greyhound to purchase MCI and eventually stop buying buses from GMC.
Although more recent buses do not sacrifice power, air ride, etc., and tend to be more comfortable and have more convenient transmissions, more luxury for passengers and the driver, etc., they also tend to have more complicated electronics and corresponding failures; many have been built with part-steel construction that leads to eventual rust problems; some have had problems with engine or transmission access; etc.
Detroit Diesel in Yellow Coach/GMC, Crown and many bus brands after 1980. The 6-71 inline was offered in a horizontal configuration suitible for mid-bus underfloor installation. Detroit Diesel was divested from GMC in ??
Hall-Scott in Crown and Flxible. Hall-Scott offered their engines in a horizontal configuration suitible for mid-bus underfloor installation.
Hercules in Fitzjohn and Flxible International in Beck and Crown.``Brills were the mainstays of Trailways and its affiliates in the post WWII era. Powerful 779 cu.in. Hall Scott gasoline engines powered these buses that could reach speeds of 80 MPH on the open highway where they could overtake and pass slower Greyhound buses much to the delight of passengers and drivers alike.''
``Averaging 2-3 miles per gallon of gas along with higher maintenance costs led Trailways to begin replacing the Brills with more economical diesel powered coaches.''
[PBMa 01][PBMa 01] Web page on the Pacific Bus Museum's Trailways ((Virginia Stage Lines) #705, From http://www.pacbus.org/pbm705picpage.htm, 2001/07/16.
Water leads to rust; freezing water can pry things apart and lead to rapid destruction. Sunlight degrades rubber, plastic, cloth, leather, paint, ... just about everything other than metal. Outdoors, branches can fall, people shoot BB's and small guns, people spray grafitti, and sometimes folks will break in to the main area or storage areas just for fun. (A friend of mine damaged his bus after driving it without coolant, after somebody reached through locked grillwork and took the radiator cap.)
So indoor storage is good if you can arrange it. Covered outdoor storage is next. Beware of just draping plastic over it, though, as you can accidentally create a greenhouse and the heat can damage things.
Also protect the mechanical equipment. From Fast Fred:
[Two axles, four big wheels. In any case, only two axles.]
Few buses were made with both center aisle access (compared to multiple side doors) and also with single tires in the rear. And I am not aware of any like that made after WWII, though I am sure there are some I do not know about. Why? it is difficult to build a large bus with single tires, just because the big bus weighs more; and larger tires cut in to the passenger space more.
So you may want to ponder a bit more how sure you are about "only four tires". You may also want to see if you can recall anything more about the size of the tires. Take a look at a picture of a Crown. Like most big buses -- until quite recently -- the Crown has "pretty big" tires. But then the body is big, too. Also take a look at the 1932 Twin Coach at www.pacbus.org under "Roster". The tires are smaller than Crown tires but they look big because the bus is small.
There is no right answer here, I am just looking for more clues.
It seems to me the door was behind the front wheel.
Again, this is a relatively uncommon configuration for post-war buses except those with the engine under a hood in front, like modern school buses. Although there are certainly some built that way, like the ACF Brill. Some modern transit-like buses are built with only a center door.
No rear windows.
Crown buses usually have rear windows, but it is always possible to cover them over. If it did have rear windows that would tell for sure that it was not a bus which, like the Flxible, was never (well, rarely) built with rear windows.
The side windows were round-cornered, probably slanted.
I believe slanted windows started appearing in the late 40's, were common by the late 50's, and started disappearing in the late 70's.
There were mid-engine buses?
Yes; ACF Brill many Crowns, and some Gilligs are mid-engine buses. Some Crowns were front- or rear-engined -- there are exceptions to every rule! If you lay the engine on it's side, it does not intrude in to the passenger compartment. A mid-engine placement avoids complicating things at the front of the bus where steering makes things cramped and there are fewer tires to support weight. Mid-engine placement also avoids problems squeezing everything in to a relatively small space at the back of the bus; it also avoids a long overhang at the rear of the bus which leads to tail swing when the bus turns and potentially complicates structural and balance issues.
Mid-engine placement also reduces under-floor storage and makes engine access more difficult. It also limits engine choices, since V-profile engines such as a V-8 do not really have a "side" to lay down on. In modern buses, it also limits the floor height, which is an issue for transit buses. Today, mid-engine placement is mostly used in the U.S. for articulated transit buses, which typically want to drive the middle wheels and have a complicated turntable and height constraints just aft of the middle axle.
Didn't seem as high or wide as newer buses, but 6'3" headroom.
Newer highway buses have moderate headroom inside and lots of underneath "bay" storage -- that makes them relatively tall. Older highway buses usually have both less headroom and less underneath "bay" storage and are quite a lot shorter. Some older highway buses have no storage underneath and instead have it at the back. Modern buses used in some other countries are built that way, too.
U.S. buses used to be mostly 96" wide and 35' or less. Over time, laws changed; roads were made wider, better-graded, and got higher weight limits; and engines got more powerful. At the same time (sometimes cause, sometimes effect) more buses got built in 102" wide over 35', and total weights went up. Today, I think most highway buses are built 45' and many city buses are 40'.
(The demand for 45' buses is in part because there are many 40' buses already, built and in good condition. As they wear out, there will probably be more orders for new 40' buses. I think it is no longer possible to buy a North-American-made highway bus 96" wide, nor under 40' long. Heavy-duty transit buses are still made down to 30' and medium-duty buses much shorter.)
I do not recall any specific movie appearances.
Here is a potentially fun homework assignment for you: somebody, someplcae, must have a list of busses appearing in movies. You could find that lsit and use it to figure out what movies to watch. You'd get to watch fun movies and look for your bus at the same time!
5 million miles on a bus -- is that something special?
Probably any vehicle can go that far, if you keep at it long enough. A friend of mine is a bicycle enthusiast and over 40 years has put 250,000 miles on some parts of his bicycle. At 10 miles an hour that is 25,000 hours or about 2 hours a day. No wonder he is in good shape! And I should get out and ride more!
I guess it also depends on how much you can replace and still call it the original vehicle. In Europe, a building is 500 years old if most of the stones that were put there 500 years ago are still there. In Asia, where stone construction is difficult and wood rots, a building is 500 years old if it has been continuously maintained and renovated regularly for 500 years -- even if none of the timbers, shingles, etc., are from the original construction.
Philosophy aside, I think 5 million miles is plausible for a heavy-duty vehicle. But not common, for at least two reasons. First, things break. Second, you have to have enough drivers keep at it for long enough and fast enough to go that far.
If you could go 50 miles an hour 20 hours a day 350 days a year, that would be 350,000 miles a year. But since you have to stop for passengers, fuel, daily/weekly/monthly/annual maintainance, and so on, highway buses usually do
![[New Look]](img/pacbus.org/images/pbm3270_small.jpg)
![[Late Century]](./img/orion-pht/Orion-1-30foot-PHT-med.jpg)
