linden

Double cluching is "rev-matching" and serves to reduce stress not only on ALL transmission parts but the clutch as well. Rev-matching is not the correct term. it identifies what is taking place, yet having driven and raced many sports cars over my 44 years I've never had someone at the track say "ya as I was rev- matching going in to turn 3 I missed my third gear down shift." It doesn't exist. I'm new to this post and I don't mean to be a hard ***. I just think that people should now the correct terms when discribing something.

jbrennen

iTrader: (1)

The synchros are more than strong enough to handle routine shifting, even for performance driving. Don't worry about that.

There are two ways to abuse the synchros. One is by shifting gears without the clutch being fully depressed -- instead of synchronizing a relatively light layshaft, now the synchros are trying to synchronize the rotating mass of the engine, which is much heavier and which has much more friction. The other is by slamming the gear lever into place with too much force. If you are using more force to move the gear lever than you can exert with just your fingertips, you are going to stress the synchros -- the synchros need sufficient time to change the layshaft speed before the dog teeth engage. And if you really slam it in hard and force the tranny into gear, you may bend or break the dog teeth which engage the gear.

jbrennen

iTrader: (1)

Sorry, but double clutching and rev matching are different techniques -- related but certainly not the same. Double clutching, by its name, refers to the technique of pressing and releasing the clutch twice during a single shift, and is generally only required on dogbox transmissions. If you press in the clutch, downshift, blip the throttle, and release the clutch, you are not double clutching, you are rev matching.

linden

I see what you are saying. Yet it seems silly. "rev matching" doesn't ease any stress on the transmission, only the clutch. why not learn how to double clutch correctly and save your tranny and clutch at the same time. Racers have been doing it for years

nebolic

iTrader: (1)

double clutch is to ensure your gears are disengaged (old school transmission) depress clutch - pop into neutral - blip throttle (to make sure the gear is disengaged) depress clutch- shift into gear).

Rev match - someone already said this but heres the jist of it.
in 5th gear your going 60mph your engine is reving at say 4000rpm
if you down shift into 4th gear doing 60mph, your engine will not spin at 4000rpm but it will spin much higher say around 5500rpm
to prevent that jerk when you downshift into 4th gear you will rev your engine (hence rev match) to match the speed of which the car is going. Also note that a lot of times when you shift your needle will drop around 1.5k to 2k. Now when people say blip the throttle, its not really just a blip, sure any **** can blip the throttle when downshift and think its "rev match" notice the term is rev match. You are matching your gearing and engine speed. By blipping the throttle that does nothing.

Hope that clears it up.

linden

This is interesting. Maybe this is why so there are so many complaints with grinding gears and such. "Old school" transmissions still had and have sychros. It is correct that race cars have straight gears which do require double clutching. Yet those tranny's get rebuilt often. Double clutching reduces stress on the sychros especially and every part in the transmission and the clutch. If one is only "rev-matching" then by down shifting at high RPMs without double clutching, and only "rev matching," then one is asking a lot from the transmission sychros alone! I understand the point of rev matching however it only serves a very limited purpose - clutch wear. Thus transmission stress and wear is probably increased by "rev-matching" and the tech was probably right that this caused the transmission failure.

jbrennen

iTrader: (1)

Good idea to learn how to do it, I agree. My Porsche 928 had a bad, basically nonfunctional, synchro on 2nd gear -- if I wanted to use 2nd, I usually had to double clutch. But other than just proving I could do it, I never actually used 2nd gear much -- it had enough torque that I could just skip 2nd gear entirely.

But modern synchros -- which are not abused -- generally will outlast the rest of the car, even without double clutching.

To say that double clutching reduces stress on all transmission parts isn't quite correct -- the throwout bearing will suffer accelerated wear under double clutching. Perhaps not enough to make a difference, but then again, it's not that uncommon to see throwout bearings fail.

stevEVO8

iTrader: (4)

I am getting in here a little late but want to add my 2 cents.

The clutch on the evos was as per Mitsus comments to almost everyone, made to be the weakest point of the drivetrain and made to slip. the slipping of the clutch as they say caused premature wear and the blueing of the disk (which they are saying is indication of abuse). WTF they cant have it both ways.

Im sure that any EVOs clutch will some miles and normal wear is probably going to have some blueing due to the clutch slipping, which by their own design was made to do.

Rev matching is done in racing with cars and bikes. if you bring the cars engine up to speed then the synchros and tranyy have less stress on the due to the different speeds on the trany and engine. Try downshifting with out blipping the throttle, then try down shifting and blipping the throttle ebfore letting off of the clucth. Its alot smoother than just letting off of the clutch. In bikes it more noticible when watching the riders right hand while getting ready to enter a corner. Also if you dont rev match when comming into a corner you can break the rear tire loose by having the engine and tranny adversly affecting the speed of the rear tire.

jbrennen

iTrader: (1)

I don't see how rev matching (in the absence of double clutching) could be reasonably blamed for transmission stress and wear.

Essentially, if you are completing the entire shift procedure with the clutch pedal depressed, the transmission (during the actual gear shift) doesn't know or care whether you are rev matching. The synchros do the same amount of work whether you are rev matching or not. Only when the clutch pedal is released would the transmission "see" the difference between a rev-matched shift and a non-rev-matched shift -- and at that point, the transmission and layshaft are fully engaged in the new gear, and the wear and stress are directly proportional to the difference in speed between the engine (flywheel) and the layshaft (clutch disc). It's difficult to make any case that a rev-matched shift puts more stress on anything than a non-rev-matched shift.

On the other hand, if you are saying that Mitsu can invalidate the transmission warranty because the driver didn't double clutch... I don't think even Mitsu wants to open that door. The owner's manual doesn't tell us to double clutch. And if they did add it to the owner's manual, they'd expect to see a lot more clutch and transmission failures due to inexperienced double clutching.

linden

I don't think you get my point. Double clutching is asking the synchros and transmission and clutch to do MUCH LESS WORK (and if done right, no work) upon down-shifting. When you are rev-matching you are still doing a normal downshift requiring the synchros to do all the work then bliping the throttle before releasing the clutch to ease the straing on the clutch and the running gear. Again this is simply requiring a lot of the transmission during hard driving - that's all I'm saying. I learned how to properly double clutch when I was 15 and have been doing it ever since on ALL my cars (never owned an automatic). Yes it might wear out the TO bearing a bit sooner. However I've never had to replace a clutch in ANY of my cars. 76k on my M3, 110K on my Tacoma. I sold a toyota PU with 135K and a Civic with 178K and the original clutchs, no slipping, going strong. Also no Transmission problems either. I do feel the Evo's clutch slipping (factory built-in) at high RPM shifts so I'm not expecting more than 40-50k from this clutch. We'll see.

rocketscience

From what I understand, modern cars with double and triple cone synchros dont really need double clutching (or double de-clutching as i sometimes hear it called). If you race your car and do it (rev matching and heelntoe) all the time, then I would practice double clutching. I only double-clutched in my 1st manual car enough to learn it but never did it after that. Never had problems with the 2-3-4 synchros. 1-2 synchro started to go soft when I sold it. But this was from 'slamming it home' on 1-2 shifts. These days I make sure I go from 1-neutral-2 instead of 1BLAM2. Still, a transmission w/ 137000 miles and just starting to wear 2nd gear synchros wasnt too bad IMO..

And obviously driving a manual CAN wear out the clutch/trans if someone is trying to learn all this on their 1st manual car esp 4wd. Thing is, no one here can say for sure it was this or that which caused the wear. We're not him and we dont drive with him every time nor do we drive his car. It could be his car, it could be him. No offense Budlong.

jbrennen

iTrader: (1)

No, I got it perfectly.

My point was that:

Double clutching -- less wear than just rev matching.

Rev matching -- less wear than not rev matching at all.

For Mitsu to say that a tranny problem was caused by rev matching... ludicrous.

I could understand -- sort of -- if they said the problem was caused by a poor attempt at rev matching. But then that's not rev matching at all. By definition, it's only rev matching if you do it right.

SoR

iTrader: (19)

I think this discussion has gone way too far with the double clutching, rev matching and shifting techniques.
Over in Europe you have ****load of diesel cars with as much torque and ladies that have never heard of rev matching not to mention double clutching, drive them daily and there are no problems for hundreds of thousands of kilometers. Now all of the sudden we're discussing here how you have to double clutch not to break the tranny in your brand spankin' new Evo with 1000 miles on the clock which probably has more robust and better made tranny than some POS diesel.
The clutch I can see could go if you slip it too much, rest your foot on it while driving or just launching it daily on high rpm but to kill the tranny in less than 50k miles with *regular roads* driving no matter how hard you drive it I just don't see possible.
My $0.02

Mxt 1

let me get this straight. is this thread about matching revs on downshifting to keep the rpm in tq range or is it about how your transmission died from engine braking? cuz you know the latter puts a bit more stress on the tranny regardless how fast you were going. so if this is the case, then i agree with the dealer on the premise that "rev-matching destroyed your clutch."
btw, this is in no way a knock on your driving style or technique. i just dont do those immature stuff. it could just be the fact that your car had an inherent problem or could've been test driven or something.
also, you should most definitely fight this warrantee crock of isht. if the dealer can bend the agreements, then so can you and your lawyer. good luck dood

Az3ar

iTrader: (18)

give me any car in the world, any car. i can abuse it, brake it in less than a day. i have done it with many cars. Sorry about your problems man hope they get better.