granny shifting and double clutching

[myeclipseisnicer]

whats the difference between the two and can u please explain each of them. thanks

[RockinWRX]

Double-clutching is something truckers do to avoid grinding the gears on their unsynchroed trannys. Start off in a gear , push the clutch in , slide the shifter to neutral , let the clutch out , push it back in , slide the shifter into the next gear. Its totally unecessary on modern cars , and was basically Vin Diesel ad-libbing bullshit in TF&TF.
Granny shifting? I think thats where you push the clutch pedal all the way to the floor before moving the shifter out of gear. The way I shift , by the time the clutch pedal is on the floor , the shifter is in the next gear. I beleive the total opposite of granny shifting is not using the clutch at all......... Possible , but I don't recommend it on DSM's or any other car with a weak tranny.

[turbo2nr]

i taught double clutuching was..

lets say your in 2nd and you going to shift into 3rd, usually you just press the clutch down and change gears..

i taught double clutching was from 2nd drop it into neutral rev the engine and den drop it into third to get the rpmz up..

1

[xjryan]

Hmm, that doesn't make much sense to me, because when you go up in gears, you don't want to rev the engine, because the engine speed has to be a little lower. When you shift down in gears, you want to rev the engine to try to match the engine speed with the gear you're going into. RockinWRX explained double clutching correctly. The thing I don't get is this... why do you have to press the clutch in twice. Can't you just press the clutch in, shift down a gear, blip the gas and let the clutch back out? This is what I do, because it gets rid of the lurch when going down in gears, plus I think it saves the syncronizers a bit. Why do they say to let the clutch out, then put in neutral, then put clutch back in, then shift into gear, then let clutch back out again? Seems like your letting the clutch out once more than is really needed.

[turbo2nr]

The thing I don't get is this... why do you have to press the clutch in twice. Can't you just press the clutch in, shift down a gear, blip the gas and let the clutch back out? This is what I do, because it gets rid of the lurch when going down in gears, plus I think it saves the syncronizers a bit. Why do they say to let the clutch out, then put in neutral, then put clutch back in, then shift into gear, then let clutch back out again? Seems like your letting the clutch out once more than is really needed.

is that ment for wrx or me?

1

[LandoAWD]

Originally posted by RockinWRX
Double-clutching is something truckers do to avoid grinding the gears on their unsynchroed trannys.

The only thing in the thread that matters.

[MB38]

There are two methods for double-clutching. Both descriptions assume a 4-3 downshift.

Standard: Clutch. While you move the gearshift into 3rd, rev your engine to approximately the engage point of 3rd gear. That way, when you release the clutch in third, there won't be a rough jolt, just a smooth transition to engine brake.

Heel-Toe: Have your left foot on the clutch and your right foot with its heel on the brake and toe on the accelerator. Depress the clutch and the brake. While downshifting, use the brake pedal as a pivot point to push your toe onto the accelerator to meet the 3rd gear engage point. Release the clutch, move your foot from the brake to the accelerator and drive away.



And not everything you hear in The Fast and The Furious is right. Obviously you're getting this from the opening race scene... a scene in which nobody would have any reason to downshift.

[LandoAWD]

Thats rev-matching, and heel-toe shifting.

[MB38]

As an addition to the above:

Double clutching is used for when you need a boost of power. That avoids the jolt of engaging a lower gear, which slows the car considerably. By revving, you avoid the initial engine brake, letting you move to acceleration faster and easier.

If you're downshifting to engine brake, you can double clutch to avoid the jolt, but you'll get more efficient engine brake if you don't double clutch.

[turbo2nr]

and heel-toe shifting rulez!
ironicly the "heel and toe" is a reggae dance also
lolz

1

[GaLaNt_DOHC_89]

You gotta hear about how the newbie racers in Alabama do it. They're racing right, lets say there in 3rd gear, they keep their foot on the gas and then just push clutch in for a second or two, just long enough for rpm's to almost hit redline, and then they let the clutch out. It is the stupidest thing I've ever heard of. It almost knocks the tranny out from under the car. I don't know a whole lot about 5spd tranny's but I do know that is not double clutching.

[MB38]

I've seen a tenth or two of a second knocked off a quarter mile time by doing that. It may not be the best thing for a transmission, but unless you've absolutely mastered a millisecond shift, it's the best option for running the occasional quarter.

[LandoAWD]

Originally posted by GaLaNt_DOHC_89
You gotta hear about how the newbie racers in Alabama do it. They're racing right, lets say there in 3rd gear, they keep their foot on the gas and then just push clutch in for a second or two, just long enough for rpm's to almost hit redline, and then they let the clutch out. It is the stupidest thing I've ever heard of. It almost knocks the tranny out from under the car. I don't know a whole lot about 5spd tranny's but I do know that is not double clutching.

No big deal with a stutter box Not the best idea in any case

[mikegee]

wasn't my car it was a while ago ,i was driving my work's mitsubishi cushman. (if you ask bout the cushman ill tell) and i've shifted from 1st to 2nd with out the clutch. no problem even made the tires chirp in second.

[kjewer1]

Double clutching has been correctly describedabove. Its similar to rev matching (uesd only on a downshift) but slightly different. Since someone asked, I'll explain the reason for letting the clutch up in nuetral. There are three systems at work here, and they all move at different speeds, and change relative to each other in different gears. The first thing is the motor and clutch. The last thing is the drive wheels, drivetrain, and output shaft of the tranny. The middle one is what most poeple forget. The input shaft. The output shaft is locked to the drivewheels, so its speed is consistent with wheel speed. The motor speed is controlled by the gas pedal when the clutch is in. As long as you are in gear, the inputshaft speed is determined by the output shaft speed (and whatever gear is engaged) when the clutch is in. Now the scenario that most poeple overlook is when you have the clutch in, and the tranny in nuetral (dont forget you go through nuetral every time you change gears ). The input shaft is allowed to spin down.

Now when the input shaft spins down while shifting the speed has to be match by two things. First is has to match the speed of the output shaft when you select the next gear. Then it has to match speeds with the motor as you let the clutch up.

In a modern syncromesh tranny, the speed matching between the input shaft and output shaft is done by the synchro. Pretty transparent to the user unless the synchros are worn (it will grind). So all thats left to do is rev match so the motor and tranny are at the same speed when you let hte clutch up. For modern cars all that is needed is rev matching, and if you want to do it quickly, use the heel toe tecnique.

On older cars where there arent any (good) synchros, you need to match the speed of theinput shaft to the speed of the output shaft yourself. So here is the scenario, Asuming a 4-3 downshift. Clutch in, revs start to fall, as you switch gears passing through nuetral the input shaft speed falls, output shaft speed is constant with wheel speed. Let clutch up and rev match to bring the input shaft up to speed, clutch back in, engage next gear, rev match again if necessary and let the cluthc out. If you let the clutch up in nuetral but dont blip the throttle, you did nothing for the synchros, and its not double clutching.

Its really simpler than this, but its a lot to expalin. Hope it helps.