Truck vs car manual tranny

You can float the gears in a synchronized (automotive) transmission. However, because the synchronizers will not allow the gear change to happen until the gear speeds are matched, unless you get the rpms exactly right every time, the synchro's will wear out rather quickly. The transmission will then grind between gears even when using the clutch... that is unless you were to double-clutch it... or float the gears like a truck.

Besides the synchronizers, another problem with floating the gears in a car is the relatively light weight of an automotive flywheel. The engine will return to idle fairly quickly, thus slowing the input shaft at the same rate, making the shift window happen very quick--you gotta be quick on the stick to make it happen. The lighter the flywheel and the smaller the engine, the harder it'll be to float the gears.

A bit of trivia... an old racer's trick is to grind every other tooth off the synchro's--makes the tranny easier to speed shift (full throttle).

In a manual transmission, the gears are always meshed between the mainshaft and the countershaft. These are the gears that everyone refers to being straight cut or helical cut. The way the gears are cut only affects how quiet the transmission operates. The sliders are the parts that do the actual shifting and they are always straight cut.

You can tell a straight cut from a helical cut tranny just by listening to it--straight cut gears whine while in operation and helical cut gears are relatively quiet. Sometimes there is a mix even in the same transmission, probably due to cost considerations--helical gears cost more to machine. If you've got an older pickup truck with a manual, listen to the way it sounds in first and reverse gears. First and reverse will usually whine and then it magically gets quiet in the higher gears. This is because first and reverse gears are the same gearset on the shaft... and straight cut, a reverse idler is used to change the direction of rotation--the higher gears are helical cut.

Someone earlier touched on the clutch brake. I have yet to get in a older truck where the clutch brake is not completely worn out and trashed. NEVER depress the clutch all the way to the floor while the truck is moving--this is instant death for the friction material. The clutch brake has one purpose and one purpose only--to stop the input shaft from turning upon depressing the clutch all the way to the floor while the truck is sitting still. The reason for this is because the sheer weight of the spinning input shaft tends to keep it in motion for a long time after depressing the clutch. The clutch brake allows you to stop the input shaft almost instantly after idling in neutral, so you can put the truck into first gear. Otherwise you have to wait for the shaft to stop spinning by itself which can take a while. If you've ever driven a truck where it goes "C-R-R-R UNCH" when you put it in gear, the clutch brake is gone.

Anyhow... sorry for the novel--just trying to put the info out there.

 

Reference was made to gear changes with no neutral such as motorcycles, splitters and range changes. My favorite "no neutral" is the support leg gearbox.

Reference was made to the rapid deceleration of gas engines due to lightweight parts throughout the engine and clutch/flywheel. Rapid deceleration is also caused by the vacuum pump effect when the air supply is cut off in the air box or carburetor. Shifting a spark plug engine is similar to shifting while using the engine brake on a diesel.

 

The 4-speed transmissions used for NASCAR racing are designed to be shifted with or without using the clutch.

 

well heres how i do it... if im downshifting from 10th to 9 i match the road speed with the gear i want to be in if im doing 55 im in 10th so if i want to go to 9th gear i slow the truck down to 45 mph then shift into 9th and same with upshifting 15 mph=6th 25 mph=7 35 mph =8th and so on 1+5=6 ya understand? i try to make it plain as can be lol it truly isnt as hard as some make it to be

 

" Do you have to remember what speed should be in what gear at all times?"

Learn a few shift points such as how fast will the truck go in low range, and what gear do you usually use when making a right turn.

Most trucks can not be shifted into a gear that is too low for the speed you are traveling. Of course, there are those idiots who will really jam it into gear and the sudden shock will blow the clutch.

Here is a hint. If you don't know exactly what gear to try after slowing down, try one that is probably too high. It will go into gear, but the rpm may be too low for power. At that point, you can downshift one gear and it will be just right.

 

If y'all can't find 'em --- grind 'em.

Shift by ear --------
If the grinding sounds high-pitched,.......
your rpms are too high. Errrrrrrrrr..........
If the grinding sounds low-pitched,........
your rpms are too low. Grrrrrrrrr.............

If y'all hear, bam, bang, boom, ka-powie, snap-crackle-pop, thunk,
thunk, thunk --- around the same time y'all feel the Big truck shutter, shake & rattle,
pull 'er over and call Road Service.
Just mention "transmissing" and/or "U-Jointlessness."
(in pieces on the ground)

I think they'll understand.
But, don't be surprised to hear that the "fix" will be,..................... "You're FIRED!"

And, on the way back home --- sit up front.
I'm sure the bus driver will get a kick outta your experience. Probably keep 'em awake.
Laughin'.

Just a thought I think I thunk.

 

Hmmm. I don't remember not being able to push the clutch in all the way to the floor in shifting a truck tranny. I was reading another thread on here about using the clutch, so, for the fun of it, I drove my truck around town double-clutching. I remembered why I hated it so much. It's a freakin' pain in the #**. I quickly reverted back to floating, save for getting the truck moving from a dead stop.

AS far as knowing which gear to put the tranny into when you have had to slow down. I don't look at anything, I just do it by sound and - experience I guess. Drive a truck long enough and you start to consider your right arm/hand an automatic transmission. It does all the work for you and you don't really think about it. In fact, I get myself into trouble if I DO start thinking about it. I am in city traffic all day long, I have to shift - allllllll day long. To have to exert very much energy or thinking into it would be - intolerable. ESPECIALLY double-clutching. Why would anyone want to push a clutch in twice to do something that you can do without any clutch peddle movement at all? The stick drops it into the gear without a thought - no grinding, no crunching noises, just a nice, beautful nothing.

As for 18 speeds - well, it's just more gears. It really isn't any more difficult than a 10-speed and - well, they behave the same as any other truck tranny in shifting- floating is definitely the way to go!

 

"The only automatic transmission I need is installed between my ears." -- This is something I've said in the past, and by and large it rings true.

When I'm in a manual-transmission vehicle- even a motorcycle, my brain becomes an integral part of the man-machine bond. The most vital part, in fact...

With practice comes experience, and with experience comes understanding.
I'm sure it's no surprise to y'all... but most of the "driving non-drivers" I know either cannot fathom how I survive without an automatic transmission, or without a cruise control, or without intermittent wipers, door locks or power windows for that matter. I'm sorry, I don't need to spend $10,000 extra for a pickup that tries to think for me!

 

PTX ----
By Golly!
You're a regular Mr. Machine!

I can identify with what you've stated.