APeteSS

I have lapped in fair number of good track cars (911s, 360s) at road courses such as Willow Springs and Laguna Seca, nearing the lap times that some of the testing guys I know can run.

I do some auto-x and track days in my SS these days.

But I have always wondered...
In all my driving--no matter what the car--I've never double-clutched. I know it's technically the correct way to downshift while heel-toeing, but I cannot see how it is faster or more efficient to release the clutch, even if only half way, to blip the gas between gears on a downshift. Does double-clutching save the clutch or something?

Please... Enlighten me

jRaskell

iTrader: (1)

Double clutching isn't necessary on a tranny with synchros. The original purpose of double clutching was to get the dogs of the gear you're shifting into in synch (it actually get the dogs for all the gear synched up) so you can engage them easily when you shift it into gear. Today's trannies have synchros that keep the dogs in sync at all time, so there is zero reason to double clutch. Nobody double clutches anymore, not even professional race car drivers (or rather, especially not race car drivers). I had an old Ford Escort GT about 10 years ago that had a bad synchro for 4th gear, so I had to double clutch when shifting into fourth or I would just grind the gear.

APeteSS

perfect, exactly what I wanted to know. Thanks Raskell

APeteSS

wow, that dates me. Shows how young I am. Spoiled, born in the 80s, never had to deal w/ synchro-less trannys

Cal

iTrader: (1)

If you don't do something to match rpm of the gears, you're going to have worn out synchros before long, depending on how much down shifting you do. There's been many a T56 fbody returned to the dealer on warenty because some kid thought it should shift from 6th directly to 3rd simply by forcing it in. If the dogs were automaticaly lined up all the time, we would never have that situation were you can't return the shift lever to 1st gear when stopped.

jRaskell

iTrader: (1)

Could you explain further? I've never had a problem putting it back into 1st gear myself.

As for downshifting, going down a single gear at a time is no problem. I can't attest to any problems downshifting multiple gears at once though. I've only found myself doing that on fairly rare occasions. In a racing environment you should never find yourself doing that. On the street, <shrugs>. I have done the 6th-3rd shift a couple times myself to quickly respond to a... situation, shall we say. I think I've only done it a handful of times though. I don't want to insult anybody, but if you're returning your tranny to the dealer for warranty repair, it's one of two things, faulty part in the tranny or driver.

Cal

iTrader: (1)

Many owners have complained that they sometimes can't get back into 1st after stopping at a light. It's a rare occurance with my car, but it's happened a couple of times. Usually going into some other gear then trying 1st again will move the dogs just enough so it will go in. Or even feathering the clutch a bit.

The people I've seen on various message boards with synchro problems had never heard of double clutching or rev matching when I asked. I suppose there could be some defective trannies out there, but not as many as I've seen with complaints. The T56 is the stongest and most forgiving of all the manual boxes I've ever had.

myZ

So Cal are you saying that there is a direct correlation between downshifting right and your tranny not wanting to find first at a stop? I remember asking a question like this a year or so ago when I first bought my car and it would do this (not go into first) only when coasting up a off ramp in neutral, then when the light would turn green it would not go into first. So if I were to downshift by rev matching it would not do this??? I just find it hard to rev match in every day driving because I’m in 6th gear under 2000rpm most the time so I get little, to no compression braking, I don’t see the point in street driving…see what I’m saying??? If I were to down shift from 6 to 4 and then from 4 to 2 maybe then I wound be around 3k rpm and then get some assisted braking. So I guess so far I leave heel toe downshifting to the track(which i cant do...i'll blame it on the pedals) or a 6th to 3rd rev match to the street (in which i dont have to use my right foot on the gas and brake). Any advice??

Cal

iTrader: (1)

Yeah it's hard to heal-toe with the sides of your foot like you're supposed to in these cars unless you have duck-feet! I put a wider gas pedal on my car, and my ankle thanked me for that! I agree, it isn't necessary for day to day driving, just a racing technique. But if it's convient to do so, why not make life a little easier or your synchro's?

As far as downshifting into first, yes it will go in every time if you double clutch, as long as you do it before the car comes to a complete stop! You will also find you can downshift into first at higher speeds, and with less force on the shift lever. It just "feels right" if nothing else.

I was in a situation just today at an autox where these skills came in very handy: Going into a tight hair-pin turn that bogged the motor on the way out if I stayed in second, but a little fast to be downshifting from 2nd to 1st without breaking traction. By double clutching, I was able to do the down shift smoothly and exit without bogging the motor OR breaking traction. Then I simply short shifted back to second after done exiting. In this case I wasn't braking anyway, so it was very easy to stomp on the gas while in neutral, not needing to heal-toe.

jRaskell

iTrader: (1)

I know what you're talking about now Cal. Actually, I've always known. The reason I don't skip gears when shifting anymore is for that reason. It's just been so long and become so natural for me to shift the way I do now that I don't really think about why I do it this way anymore.

I was thinking about this thread coming into work this morning because for the most part, when I jump on the Highway in the morning, I'm up to my 75mph cruising speed in 4th gear, but I still shift into 5th then into 6th, even though I'm in 5th for only about a second. And anytime I'm downshifting I just drop down a single gear at a time, even when it's only for a second or two.

So this time around, when pulling away from the toll booths I get up to cruising speed in 4th, then instead of shifting into 5th, I pop it in to neutral, release the clutch for a brief moment than press it in again and slide it right into 6th much easier than I would have done without the clutch pump.

Just goes to show it can never hurt to question your own knowledge from time to time. You never know when what you know isn't really what you think you know, know what I mean?

BaD FiSh Z28

with rev matching u can shift without using clutch although its real slow what u do is well for instance say ur in third and ur driving when u go to shift u can take it outta gear no porblem but then it doesnt wanna go into fourth u rev it up and u will be able to feel it in the shift *** when it will go in but.....
u have to be careful dont apply comnstant pressuer cause then u will just grind gears u just wait till it feels loose again and throw it in fourth but i wouldnt recomend it unless ur trying to save ur clutch if its about to go out its not a very safe way to drive and when u rev it up wait till the rpms are coming back down to shift in gear cause there is a bigger opening cause they dont fall as fast as they go up

Blakbird24

iTrader: (24)

With my size 14's, I have gotten into the habit of heal-toeing pretty much all the time. The way I drive I use brakes very lightly...regardless i'll probably go through my clutch fairly quickly. I've never had a problem with the T56 not going into ANY gear I wanted to (as long as i'm paying attention and not putting it in 3rd instead of 1st ). On highways I always use the 4-6 shift, and as long as you time your clutch engagement, you should have ZERO resistance going into 6th. If double clutching makes it easier for you, go for it...it's not going to hurt at that speed. But in the lower gears, if you know what you're doing, it's nothing but a waste of time. Also I usually skip-downshift...most often 5-3-2, i've had no problems finding gears...I just pop it out of 5th and move the stick to the 3rd gate while tapping the throttle and applying light pressure to the stick, then the shifter will pop into 3rd when ready.

Cal

iTrader: (1)

JRaskell, you can double clutch for upshifts, but it's rarely if ever needed. Double clutching is to help with downshifts only. If you do double clutch and rev match, you can skip one or two or however many gears you want to with no problems at all. Maybe this explaination will help:

The job that syncro rings and clutch dogs have is connecting two shafts together that are often going different speeds; obviously this is a hard job and the dogs can grind at worst, and at best the rings have to do a lot of slipping kind of like your clutch does to get the car moving. One of these shafts is the tranny input shaft, the other is the output shaft. The output shaft is always connected to the wheels so it's speed is fixed by the car's speed. The input shaft is connected to the motor, but only when the clutch is engaged, so you have control of it's speed anytime the shift lever is in neutral. If you are up shifting, the speed difference between the input and output shafts takes care of it's self: with the clutch disengaged and the shift lever in neutral, it just naturaly slows down, so you don't need to help it. But when you down shift, the input shaft will need to be spinning much faster than before, so you let the clutch back out while the shift lever is in neutral, then rev the engine to the new rpm. As mentioned by bad fish, if you can do this perfectly, you don't even need to use the clutch. However, don't try this as most of use aren't that good.

But do try this: Once you get out on the freeway going 65 or 70 in 6th gear, push in the clutch, push the lever up into neutral and let it self-center on the springs, let the clutch back out and rev the engine to 3000 rpm and hold; now push the clutch back in and pull the lever straight back into 4th gear, and finally let the clutch out as you push the gas the rest of the way to the floor. You will be amazed at how the shift lever slides easily and quickly into 4th, and how the car will smoothly but firmly accelerate. You will like the feel of this, I guarantee it!

Cal

iTrader: (1)

Yes, that works because there is always some friction between the clutch and flywheel even with the clutch disengaged. So actually, you can rev match without double-clutching just by reving while in neutral. I'm not sure if this is reliable in all types of cars, but it does seem to work in ours and it saves a step. I personally don't trust this because I drive a lot of different vehicles, but that's just me.