my friend has a saturn and inorder to shift into second gear you have to double clutch. its not cuz its an old trany where you always have to double clutch but it is DEFINETLY cuz her synchro on second is screwed. what i want to know is why does double clutching let the tranny go into second when you couldnt with just a regular clutch?

I know that double clutching makes it easier on the synchros some way, (thats what i was told) but i have no idea why double clutching takes of some of the stress r w/e on the synchros.

I apologize because i didnt really search much about this cuz im in a hurry so... thanks

 

I think double clutching can blow your car up...I saw it on tv so it has to be true.

 

"double clutching" is a misunderstood term IMO. I think the real meaning of it refers to when you are rev-matching to down-shift like while autocrossing. Any other ideas/thoughts on this?

 

I'm not a mechanic, but here is my layman's interpretation:
The role of the synchronizers is to match the speed of engine to that of the transmission and the driveline. Therefore, if you down shift to slow down, if you clutch aggressively there is a lurch and in increase in RPMs. If you double clutch when you downshift. You match the revs of the motor to the appropriate RPM of the driveline and transmission. Therefore the synchronizers do little work. Autocrossers(and other road racers) use the heel-toe technique to down shift while braking. This allows them to match RPMs when down shifting, preventing wheel spin. This allows a better, smoother way to enter a corner. A benefit is it prevents wear on your synchronizers, because you do some of the work for them.

 

^ +1

 

there is a difference between rev matching and double-clutching but they get interchanged sometimes.

Rev matching is just a quick blip of the throttle to bring the revs up while downshifting, and pushing the clutch in only once, which still requires the synchros to do some work.

Double-clutching matches the speeds of the input shaft and output shaft of the tranny, doing the same job as the synchros. Input shaft is connected to the motor by way of the clutch; push the clutch in and it disconnects the input shaft from the motor.

The input shaft has the gears on it and the output shaft has the matching set of gears that are all locked to the output shaft. When you put the car in 'gear', it locks the input shaft to one of the gears and that's basically how it selects a gear. So, if you're in neutral, no gear is locked to the input shaft. If you're in neutral, but the clutch is out, then the input shaft is attached to the crankshaft and spinning at the same speed as the crankshaft. If you're in neutral and the clutch is pushed in, then the input shaft is just sitting there not connected to anything.

So when you double clutch, you push in the clutch, put the car in neutral and let the clutch out. Now the input shaft is connected to the crankshaft but not any gears. You then rev up the motor which revs up the input shaft (hopefully to the correct speed). Push clutch in, put car in gear which is now easy because the input shaft is already spinning the correct speed, and let the clutch out to reconnect the motor.

 

thanks, so let me clarify what you said. So if ur in first, press in the clutch, rev the car to the correct rpm of the crankshaft (w/e the wheels r spinning to match the gear) and while at the correct rpm you put in into the desired gear, then release the clutch. you didnt help the synchros at all cuz the input shaft (is that the one the gear selector is connected to) was not speeding up at all cuz the clutch wasnt connected? Am i understanding what you said. because i understand how the "double clutch" helps now but i always thought that what i just described was in essence the same thing.

 

What you described is rev matching, basically matching the engine speed to the output shaft speed. Double-clutching is to match the input shaft speed to the output shaft speed so you can get the trans into a gear. It literally requires you to operate the clutch twice.

1. Disengage clutch
2. Shift to neutral
3. Engage clutch while revmatching
4. Disengage clutch
5. Shift into gear
6. Engage clutch

 

That's a rev matched shift. Double clutching you clutch out of gear, let the clutch out, push it back in and then clutch again to get into gear. www.howstuffworks.com

otter and I posted at the same time. He's right and clearer. Read his post.

 

o so its what i said, it doesnt affect the gears or synchros at all. i know what i described is used in racing like spdracerut metioned and also for a smooth ride, but i thought i did both.

Thanks

 

Your post made no sense. Do you press and release the clutch fully TWO times during a shift into 2? if so you just double clutched. If not you rev-matched.

 

yeah what i was refering to was revmatching. i doesnt matter cuz i know whats up now