Double Clutching

[ctrcbob]

Originally Posted By: dsmith41
So it is not needed on a manual transmission with synchros. Why don't big rig tractors have synchros in their transmissions?

On my motorcycle, I can't really double clutch it because the gearbox is sequential, but when downshifting, I still should rev match, right? I just want to make my clutch last as long as possible and I find this sort of thing very interesting.

Actually, when going from 5th gear on my motorcycle to a complete stop, I think it would be better on the clutch to just pull the clutch in and leave it in until I have stopped completely and am ready to accelerate again. Of course I downshift through every gear as I slow down but keep the clutch lever pulled in the whole time. I just use the brakes 100% to stop the bike.


The car transmissions have a synchromesh transmission. Your bike has a constantmesh transmission.

What this means is that the synchromesh gets out of gear each and every shift, and when placed in the next gear, the drive and driven gear have to mesh together without grinding. In order to do this, the synchros get the two gears to match speed so they can mesh without grinding. You always go through neutral when shifting from one gear to another.

Your bikes constantmesh transmission has the gears always connected to each other vis the input and output shafts, but not output to the rear wheel. Then an additional device (forget what it is called) that has shifting "dogs" on the side, engages the matching holes in the sides of gears in the input and or output shaft, to make the connection. This is why you don't have to go through neutral with the constant mesh transmission. (the only reason to have a neutral in a constant mesh transmission is when you want to let the engine run without holding in the clutch). Some race cars, like F1 and Indy cars use Constant mesh transmissions. All the driver has to do is push the shift lever forward or back to shift gears. None of that shift gate in a Synchro mesh.

 

[jmaster]

man f___ those double sticks! shifting two transmissions, thats just crazy.

 

[Dualie]

[censored] Mack had a triplex box with three sticks.

I was taught to "twin stick" by an old salt in a POS GMC truck with inline 6 cylinder gas burner and 4+4. If i messed one of the range shifts or forgot to shift one of the boxes before leaving a stopsign he would punch me in the arm. (Hard i might add.) Made me a much better driver for it though.

when i spec'ed my 06 T-800 Heavy haul I went with the 2050Ft. lb. rated 18spd. 127,000 Lbs on five axles Low Low saved my rear end countless times pulling out of jobsite's in deep dirt and loose soil or sand. Getting the beast rolling on big hills. You definitely needed to be a surgeon coming off of the clutch in low low fully loaded or you would be shattering parts.

Shifting twin sticks is a dieing art form. Every twin stick truck had its own rhythm and flow that you needed to get in tune with if you were going to run any miles in it. IF you couldn't get that rhythm down you were going to fight her the whole way.


You could even spec 6+5 or 5+5 gear boxes where both boxes were OD. you could "shove both sticks against the dash" and with enough motor have a "triple digit truck"

 

[mechtech2]

ctrc bob - You have it backwards. Normal cars have the gears engaged [meshed] all the time. Bike transmissions actually change[move] gears.

 

[jmaster]

man i actually want to drive a twin stick now after watching a bunch of those vids. of course i haven't driven a rig before and don't have a cdl. i was thinking about taking classes and getting a cdl and working in that feild. theres a school in detroit that garentees a job when you finnish the 4 weeks of training. but i'm still thinking about it.

 

[jmaster]

yea as long as the engine is in its powerband it'll keep going. thats cool

 

[mjoekingz28]

I am curious as well. I can only figure it is some sort of timing thing for the body and has zero mechanical relevance.

 

[BigD1]

Originally Posted By: Doug Hillary
My trucks all had 18sps but they were all driven as 13 speeders


13 speed was what I drove most of the time during my trucking career because I never pulled anything over 80,000 pounds. Just a freight hauler. No flat bed heavy haul stuff, so those extra gears on the low side were not needed.

 

[lexus114]

Originally Posted By: Doug Hillary
Hi,
Drew99GT - Good description. "Breaking" the drive on constant mesh boxes is all that is needed as you are simply locking one gear to another. Failure to do it correctly can cause damage with a countershaft (most in Class 8 trucks (Eaton-Fuller Roadrangers) have three) bending a real and very costly possibility

It is possible to shift clutchless but this raises the risks of damage a hundred fold!


i was an otr driver for three years and learned how to shift with out the clutch. only used it for starting and stopping. but it is a tecniche that one must learn and master first. or damage will occur..

 

[Silk]

Originally Posted By: mechtech2
Normal cars have the gears engaged [meshed] all the time. Bike transmissions actually change[move] gears.


Thread dredge !

No, a motorcycle gearbox is the same as a car or truck - constant mesh gears with sliding dogs engaging gears to shafts. There are very few sliding gear transmissions around, reverse is a sliding gear, but that is fast disapearing too.

Some truck I've driven were impossible to shift with the clutch - once out of the 1st/rev gate, the lever was in the middle of your leg. A company where I worked, probably the same where Doug Hillary retrained drivers...problems where drivers were preselecting on the button, like they had done with Eaton 2 speed diffs. The RR was direct air shift.