Hi! I'm a non-trucker, but I've been interested in just how a truck tranny work, with so many gears and all. Now that I've read descriptions and explanations here and elsewhere, and watch a few Youtube videos (very informative!), I have a pretty good idea how they work.

My question is, truck tranny seem to be quite different than car manual tranny! Some definite no-nos in car tranny are in fact the regular way to do it in truck tranny, and vice versa. For example, in a car you have to floor the clutch to shift, in truck you have to depress it halfway only (except when stopping) and in fact you shouldn't depress it all the way in. Another example, in car you would never, ever move the lever without the clutch, it's considered very bad! Yet that's how you normally do it in trucks. Heck, in car, even resting your hand on the lever could cause the synchros to wear out quicker. I still can't quite imagine how one shifts without using a clutch. In car it will grind like hell if you try! Not recommended unless you're in a rental!

So when you guys drive a regular car with manual tranny, did some bad habits (yet good in trucks) carry over? Or for newbies, do you occasionally floor the clutch when driving a truck, probably cause some grinding noises?

Another question: should you have to slow down quite a bit (but not stop), say from 55mph to 30mph, how do you know then what gear you should put the tranny into? Do you have to remember what speed should be in what gear at all times? For 18 speeds that is quite a lot to remember, plus what if you're not familiar with the truck (just got it, etc.)? Considering you have to match the rev. In car there's only 5, 6 gears at most, and the choices are pretty clear, and you don't have to match rev, the clutch will take care of that. If you put it in too low a gear the engine would just rev a bit more when you let up the clutch, and that's all, as car engines have more rev range. Well, so long as your choices are not so boneheaded, like 1st at 50mph!

Diesel engines don't turn as many rpm's as gas engines do. Their optimal operating range is usually between 1400 and 2100 rpm. Drop below 1400 and you will "lug" the engine. Not good in a diesel. If you go over 2400 and you can damage the engine. It wasn't designed to run at higher rpm's. Each gear in the transmission is engineered to keep the engine in its rpm range for the speed your going. Speeds will vary due to rear end gearing. It sounds complicated but you catch on pretty fast. Years ago it used to really be fun when some of the older trucks had transmissions with 2 sticks. YouTube has a good video of a guy driving an old B model Mack with a duplex transmission.

Yeah, I saw that. That was wild!

in regards to the question of 55mph to 30,untill you are familar with that truck,it is best to drop down 1 gear at a time to get in the proper gear for that speed. thats why you'll hear trucks downshifting as they are slowing down. it is never good to float in neutral to find a gear as this can be hard on the trans trying to find the right gear. usually you can drop 2 gears if you slow the truck down by 900-1000 rpms WHILE IN GEAR,then drop 2 gears(brake untill 1000 rpm's-shift out of gear-rev to 1900-drop down 2 gears).you must be able to do this quickly(2 seconds).that is why it's best to do one at a time.once you get good at downshifting, you will be able to drop down gears quickly while maintaing the proper rpm's at all times,making dropping down more than one gear at a time more of a hassle than anything.i can slow a 10 speed down 1 gear at a time really quick without worrying whether i'll choose the right gear(on a 13 speed i'll slow it down like a 9 speed eliminating the top side split gears)

But what if you have to slow down in a real hurry and did not have time to properly downshift? Such as when traffic suddenly slow (but not stop)? I guess in that situation you'd just concentrate on the braking and might forget (or not have time) to downshift?

Well it is not a "must" to down shift but it is recommended... In the situation you describe one most likely would just apply the break to slow the truck down, then do what is know as a "recovery".. Simply bump the throttle and slide it into the gear you would need to be at that speed... If you had to come to a complete stop in a hurry as you describe you would pretty much do it as you would in a car....

There a many ways to shift a truck.. Float, double clutch ext... Double clutch is the preferred method...

I have seen drivers throttle up a little to shift up as well going down..

Under hard brake you are slowing down way too fast to bother with down shifting. While braking hard use the other foot to push in clutch and shift into neutral.

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I agree with the comments, and would like to add my two cents. BGatot asked, "... do you occasionally floor the clutch when driving a truck, probably cause some grinding noises?"

Flooring the clutch will not cause grinding noises. If the truck is in gear and rolling, flooring the clutch will wear out the clutch brake. The clutch brake is designed to stop the input shaft only, but if the tranny is in gear and the truck is rolling, the clutch brake would attempt to stop the entire rig. A driver will use the clutch brake at a stop while selecting a gear. This may be necessary because the engine is turning the input shaft although the out-of-adjustment clutch is released. A driver will also use the clutch brake while upshifting on an upgrade. If the engine will not decelerate quick enough to mesh the next gear as the truck is losing momentum, the clutch brake will be used to stop the transmission in neutral and speed up the shifting process. You see, this technique is used if the truck has the power to pull the grade in a higher gear, if you can get it into that gear.

I think Johnny99's comment about 1400 to 2100 rpm is "old school". Today's high-torque rise engines operate at lower rpm. I had the owner's manual that came with a 1975 Detroit Diesel, and it allowed full throttle down to 1,050 rpm. It seems to me that cruising range today is about 1500 rpm and the governor will cut off power before 1800 rpm. One way to check what the engineers want is to set the cruise before a hill, and then see how low it will lug before the computer turns off the cruise control.

My truck seems to do best between 1100 and 1500. I can lug it down to 1100 before I need to downshift.

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Z-Lady's devoted hubby.

The reason why you dont shift like a car is one main reason, straight cut gears. Thats why you dont need to use the clutch at all when shifting, the spillter is synchronized, while the main gears are not, thats why there is no grinding. When you have to slam your brakes you just throw it in neutral, lets say you are rolling over 20mph and you are in neutral and need to stick it in gear, well in my case with a double overdrive 18 speed and 3.55 rear ends i will have it in the high gears and throw it in 11th gear, or the "1st hole on the top side" and have enough torque # around 1300rpm. Hope that answers your question.