I don’t know much about cars and engines, so maybe someone can explain this to me. Why can’t semis - thebig rigs - have automatic engines, instead of stick shifts?
10-4, good buddy!
I think most do now but I could be wrong. My wag is that the used to be all sticks because that is the only way to handle all that power.
I spoke with Wayne Greer, retired from the Ontario Ministry of Transportation’s carrier (trucking company) enforcement division, and Walter Scott, president of a large trucking company whose name I won’t divulge, about this.
The answer, basically, is that trucks generally have standard transmissions because they always have and truck drivers like it that way. There is no real advantage to using a standard transmission in a rig and several advantages to using automatic transmissions. Automatics ARE beginning to appear, but they have to overcome a cultural bias against them.
This is true in North America, anyway; don’t know about Europe or Australia or whatnot.
Trucks are commercial vehicles. That is, they need to perform their function as inexpensively as reasonably possible in order to maximize profits. Manual transmissions are less complex and cheaper to buy, and I assume they’re cheaper to maintain. Also, standard transmissions allow a vehicle to get better mileage than automatic transmissions, saving money.
I bought my first new “car” two years ago: A Jeep Cherokee. This is the first vehicle I’ve owned with an automaic transmission. While the transmission is easier to use in Hell-A traffic, I still prefer standard transmissions. With a standard transmission I can choose what gear I want or need. Often, I being an aggressive driver, the automatic transmission shifts when I don’t want it to and doesn’t shift when I do want it to. A standard transmission gives the driver more control over his vehicle.
I hate automatic transmissions, I just don’t see the point. You give up a great deal of control for what? Not having to worry about one pedal and a stick?
Another reason why automatics are not common on semis is that truckers rely on engine braking a LOT more than car drivers, which is pretty difficult to do with an automatic. An automatic transmission for a semi would also be a lot more complicated (and thus more expensive and more likely to break down) than one for a car. Car automatic transmissions usually have 3 or 4 forward gears, which is all you need when you have a gas engine that provides enough torque to accelerate over a wide range of RPMs. A diesel semi may have 20 forward gears or more, usually at least 12, because their engines only have enough torque to accelerate in a narrow range of RPMs.
Truck drivers also don’t use their clutch as much, the gears are so close to each other and the engine revs vary so little they can often shift without it (you can do this in a car too, but it is a lot more difficult and doesn’t really provide much of an advantage),
I think RickJay has it–there is a cultural bias against automatic transmissions.
I did some rig driving some years ago, and the OP was one of the questions I asked when I started. The answers I got were along the lines of, “No automatic transmission can choose gears better than I can” and “I decide what gear is right, not the transmission.” Given these answers, I’d say there is a cultural bias. Heck, even I admit that I liked using the manual transmissions in the trucks.
Just to clear up one point–truckers do use engine braking, but rather than downshifting the manual transmission to slow, it is far easier and better to use engine retarder brakes (often called “jake brakes”). Jake brakes in a truck with a manual transmission don’t involve downshifting–for more information, you should refer to the Jacobs Vehicle Systems (the makers of jake brakes) web site, which explains it better than I can.
But to return to the OP, the Jacobs site also talks about how their product can downshift in an automatic transmission:
So there are some automatic transmissions (enough to make it worth Jacobs’ while to develop one of their systems for automatics), but from what I’ve seen, the cultural bias is still going to be there for a while.
I’m hijacking my own thread here, but why do I often see signs in certain areas that say:
TRUCKERS
NO JAKE BRAKES
Is this a noise issue?
Yup. It pretty much indicates a neighborhood that got tired of hearing BBDDBBDDbdbdbddbdbdbdbddbbbddbdbbdbdbb bdddbdbdbddbd bdbbdbddbdb at all hours.
Fortunately, the lovely SDSTAFF Jill has prepared this informative essay on What are “jake brakes” and why are they prohibited in some locations?
In Australia (a country which, like Canada and the US, has a love affair with automatic cars), it is very very rare to see an automatic truck. In fact the only one I’ve seen is a garbage truck of about 7 or 8 tons. As far as I know, there are no semi/tractor trailers with automatic transmissions.
I think this is for the following reasons:
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Whilst most trucks have jake brakes, engine braking is still used, partly because the truckies like it, partly because it provides added safety, and partly because of legal regulation in the form of signs saying: :Steep descent ahead. Trucks must use low gear.
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Australia is a big country, and trucks must cover long distances in non-urban areas, so the advantage offered by an automatic through ease of driving in heavy traffic is offset by the fuel savings achieved through using a manual transmission on long hauls.
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Hi Opal
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Truck drivers like the manual’s macho image.
The signs here say, “Urban area. Please keep engine braking to a minimum”. I think that allows the truckies to use it if they really have to pull up their heavy rigs in a hurry, but encourages them not to do so otherwise. My guess is that the term “engine braking” covers both heavy downshifting, and jake brakes.
In any event, I’ve heard of a caged talking parrot living by a down grade on a busy highway which used to say “bdbdbdbdddbbdbdbdbbbdddd bdbd b b b” 
I am not a mechanic and have never driven an automatic truck, but I think an automatic transmission in a truck would have to cut the power for ½ to one second to complete a shift just like the driver does in a standard shift truck. For this to happen when the driver doesn’t expect it could be annoying and even dangerous. Size, weight and cost are probably also issues. If there was any loss of fuel efficiency, it would be a significant drawback with the low gas mileage trucks already get, and the high number of miles they travel.
The only time a standard transmission is a big disadvantage is stop and go traffic, shifting without the clutch (like all us cool 
truck drivers do) saves a lot of leg work. Even if automatic transmissions became wildly popular tomorrow, nobody would hire a driver who couldn’t drive a stick. An experienced truck driver can drive just about any standard truck without any special instruction.
When your automatic car is ‘hunting’ for the right gear it is mildly annoying, and that’s with only four to choose from and a very broad power band. In a truck, with a very narrow power band (that’s why they need all the gears in the first place) and ten gears it would be a big problem, particularly if the transmission had to cut the power to make a every shift.
“No automatic transmission can choose gears better than I can” and “I decide what gear is right, not the transmission.” These statements are not the macho BS they sound like. An automatic is going to make way to many annoying useless shifts.
An automatic transmission will not know that the driver is–
[ul]
[li]about to take a corner and wants to stay in 6th gear[/li][li] approaching an upgrade and wants to stay in a lower gear[/li][li] Hi Op…. (Forget that, Anthracite might yell at me 
)[/li][li]approaching a downgrade and wants to stay in a lower gear (for engine braking)[/li][li]approaching a downgrade and wants to stay in a higher gear (the hill will help you gain speed)[/li][/ul]
When starting out I choose from one of the first five gears based on the load I am hauling and the grade I am on, how is the automatic going to know which one to pick?
Most modern trucks have ten forward gears, nine speeds and thirteen speeds (sometimes mistakenly called eight and twelve speeds) are the next two common trannys.
ARRRG, I messed up the link…
http://boards.straightdope.com/sdmb/showthread.php?threadid=64368
From my daddy, the trucker:
“Now they’re making all these automatic transmissions because they want all these young kids to drive who don’t know how to drive standards! But the actual reason is because of all the weight you have to haul - you didn’t used to be able to get all the power you needed out of an automatic transmission. Also, automatics are for wussies.”
First off let me say that anyone who cannot drive a big truck that is equipped with a manual transmission should not be driving a big truck, at all.
There are automatic transmissions in big trucks but they are different than the automatic transmissions you would find in your personal vehicle. Also, the manual transmission in a big truck is even different than your personal vehicle’s manual transmission.
As to the differences in the manual transmissions-
Your personal vehicle has a ‘synchronized’ transmission, which means that you can press your clutch and put the transmission into any forward gear your choose (except for first gear on most cars since it is usually not synchronized). Now, if you are cruising along at 70MPH, press the clutch, put it into second gear and release the clutch, you will notice the RPMs will skyrocket (and will probably sling a rod in your engine, so don’t do this),but you were able to get into second gear. A big truck’s transmission, on the other hand, is ‘un-synchronized’. This means that the trucks road speed has to match the gear you are choosing. Being able to do this is possibly the hardest part of learning to drive a truck and is why automatics in big trucks are even in existence. With the high turnover rate of professional truckdrivers and the increase of freight to be hauled by trucking companies, there was a need to get people in off the street and into a truck in a short period of time, voila! auto transmissions.
Now, how is this done and how is it different than the auto transmission in your car?
Well, first we have to see what is different about a automatic and a manual that you would find in your car.
A manual transmission is a very simple device actually, made up of a main shaft and countershaft, each with gears of varying teeth, your shifter moves these two shafts together in different positions, thus causing different gear ratios in the different gears. One clutch separates the transmission from the engine and when you change gears, you are apt to ‘feel’ the changes as they are made.
An automatic is grossly different, as it is more of a hydraulic affair. Automatic transmission oil is really the heart of an auto transmission. When you press the accelerator, you raise the RPM level of your engine, this rotation is tranferred to a “torque convertor”, which is an oil filled device that acts like a pump and is the area that a manual transmission’s clutch would be. When sufficient RPM levels are achieved the torque convertor will “lock up” and deliver the engine’s power into the transmission. This power is delivered to the transmission’s true pump which begins the transmission oil’s journey through the rest of the transmission. There is a mainshaft but no countershaft, and instead of one clutch you have multiple “clutch packs”, one clutch pack for each forward gear (unless you have an automatic with “overdrive”, then the system changes slightly and varies by manufacturer). Depending on the driving conditions and RPM level, the transmission will go to different gears and all of this is controlled by the actions of a “valve body”, which is changing the flow of the oil to apply it to the clutch pack that is needed. The clutch pack will engage and transfer the power to the mainshaft by way of “planetary gears”. When the transmission is shifting from one gear to another, the goal is to NOT feel anything, so engineers design transmissions to “slip” a little as it changes.
A big truck’s auto transmission, on the other hand, is almost identical to it’s manual. The only distinct difference being a system of electronics and linkages that, in effect, take the place of your right arm and left foot. The transmission is the same internally but in place of the shifter, a computer controlled linkage chooses the gear for you. The computer also cuts the engine power momentarily(just as Anachronism suggested) and takes advantage of the no-clutch shifting that is rather common in truck driving ( and a really cool driver even downshifts without the clutch, if he doesn’t own the truck, right Anachronism? :)). Of course the clutch pedal is still there, but is only used for starting off and when coming to a stop.
Why do they do it this way? Well, the biggest problem that would have to be overcame, if using a transmission like the one in your car, would heat. The oil in your cars automatic transmission gets very hot and if you have an automatic in a large personal vehicle (like a dually, also called a 1 Ton Truck by non-rednecks), the oil gets even hotter and requires a “transmission oil cooler” to keep the oil from breaking down. Another drawback to slinging around all of this oil is the extra strain on the engine and the lowered fuel mileage it would cause. When you only get 5-8 miles to a gallon, you don’t want to do anything to get even less.
BTL- Allison makes a very heavy duty automatic transmission that is used in medium duty trucks and is hydraulic in nature. It is very similar to the one in your car only bigger.
This has reminded me of a thread I’ve been meaning to start, but now that it’s been mentioned here, I may as well very mildly hijack this one. I’ve seen a thread or two recently on the old auto versus stick debate, and there seemed to be a common underlying theme to them. This was that both sides of the debate seem to agree that a manual (standard) transmission is technically better. Usually the reasons cited were better handling, and improved fuel economy. The reason some people were pro-automatic was simply that they were willing to sacrifice these benefits in exchange for greater ease of driving.
One of the things I don’t like about autos is their tendency to ‘float’ the car through corners. It feels quite mushy. This got me wondering why haven’t they made an auto transmission based on a manual one? That is, have a manual gearbox and clutch fitted with servo-motors to operate them, and the whole set-up connected to an on-board computer. No torque converter, no planetary gears. It may even be cheaper and simpler to build than a conventional auto box.
It could even be fitted with optional over-ride buttons for those who wish to shift gears themselves. I may be wrong here, but I think the current “auto-manual” boxes in some sports cars are based on an auto box. So, why not base it on a manual?
Now,mojo filter has educated me that such an affair exists in some trucks. So how about cars?
Now hold on a minute here. A couple people touched on this earlier, but I think the real point is - how in the hell do you make a 10, 12, or 20-speed automatic transmission that can take 600 lb-ft of torque on its input shaft? Has anyone here seen how complicated even a 5-speed automatic transmission is? I have, and they are not simple devices. And how does one control it as precisely as a trucker can a manual transmission?
And what about cost? Yeah, big rigs are expensive, but why add a few thousand dollars onto it?
And what about the frictional losses of the automatic being greater? OTR trucking is an industry that lives on its gas mileage. How many truckers will willingly drop even one mile per gallon just to have an automatic?
I think there are some serious technical and financial aspects involved, not cultural.
Quote: Real Men Don’t Eat Quiche
Hell, real men don’t even know how to pronounce kwichee.
TheLoadedDog
An automatic can be tweaked to operate almost identically to a manual transmission, you can even have an auto trans with a clutch, if you so desire. Altering the valve body changes how the transmission shifts and can be adjusted to give very light shifts if you are wanting comfort or can give very hard shifts if you are wanting to be in the next gear before the engine RPMs fall out of the power range. The valve body can also be modified to only shift after you have manually moved the shift lever, and to hold a gear indefinetly, if you this is what you want. Drag racers have taken advantage of all of these modifications at one time or another. I think we have also seen some production cars with the ability to alter it’s shift settings “on the fly” and allow the driver to choose whether he/she wants comfort or sport shifting.(I’m thinking Corvette, but even it it’s not being done now, it is possible)
Now, could they do all of this with a manual? Yes, they surely could.
Would it be popular? Probably not.
Getting the same characteristics from a manual and having it operate automatically, would not be cost effective.
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Instead of just modifying what you have now, you would be adding linkages and electronics that would add weight and increase the likelyhood that something will break.
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When an automatic transmission breaks down, rebuilding it is alot cheaper since the parts that are usually replaced are parts that were designed to wear out anyways. When a manual transmission breaks down it usually involves a bearing failure or gear breakage, either of which can cause catastrophic failure of the entire transmission, thus requiring a complete replacement of the transmission. Even if the transmission is not completely shot, the gears and bearings on a manual tend to cost 4-5 times more than the normal wear parts in an automatic transmission.
So, if you were to go to a properly equipped shop and demand an automatic transmission based on a manual, it could be done. What you would get though, would not be any better than what a mechanically inclined teenager could get out of his Mustang’s auto, and his setup would cost far less, be more reliable and it would be more cost effective in the long run.
Would there be any advantage to a manual that operates like an auto? Yes, but I believe only one. It does take less horsepower to operate the manual so more is available at the driven wheel, but if you spent your money on the engine instead of the transmission even this would be a non-factor.
An auto with a clutch? Woah, my head hurts. Anyway, thanks for the information, mojo.
OK, I’ll chime in here. I hold a Class A CDL and I drive a truck that happens to have an automatic transmission. It is one of two old Ford dump trucks (a '78 and a '79) that we use regularly (well, we now use only one of them regularly, one of them threw a rod on me Friday, so now I’m stuck in the older one for a while…). These are full-size commercial trucks with huge (696 CID) V-8 Diesel engines. Both of them have 5-speed automatic transmissions. As a local-run driver who spends a lot of time off-road and in traffic (not at the same time, obviously), I love having an automatic in my truck. Acceleration is poorer than with a manual transmission, but I can live with it since top speed is only about 60mph unloaded, anyway. As I posted in an unrelated thread, I have a really bad left knee, so I may be a bit biased about AT vs MT, when it comes to trucks and 80lb clutches, anyway.