Can down shifting damage the trans ? it sure helps breaking just wanted to know ?

 

downshifting is fine for your car as long as you're not overrevving on the downshift. If you downshift from 3rd to 2nd at 55mph even with rev matching I don't imagine it does your transmission any favors.

 

BTW, what's rev matching? TIA

 

rev matching is bringing your engine up the speed of the gear your going to downshift into.

i.e. you're going to down shift from 4th to 3rd @ 60mph so you push the clutch in, rev to 5,000 rpm and slide the shifter into 3rd and release the clutch. saves on your synchros

 

Hey VetteKiller I didn't know that either! Cool tip man thanks!!!

 

So when downshifting from 4th - 3rd you'd rev well your still in 4th or go into neutral then rev?

Also, how do you know what to rev it to for each gear?

 

You rev it in neutral. Goes like this:

1) Start in gear, cruising.
2) Clutch in
3) Shifter to neutral
4) Blip revs
5) Clutch out
6) Clutch in
7) Shifter into gear
8) Clutch out.

What I've just described is a combination of rev-matching (often called "heel-toe"ing, since you hold the brake with your toes and blip the throttle with your heel - it's the neutral blip before downshifting) and double-clutching (steps 5 & 6). You can omit the double-clutch, since most n00bs can't do it fast enough but it slightly reduces the load on your synchros as well.

EightTrack: Okay, say you're at 3000 RPM in second, and you shift into third. This drops your revs to about 2100 RPM. What we're doing is going backwards. If you're in third at 2000 RPM, you raise the RPMs to 3000 before you let out the clutch after downshifting - get it?

Listen to a race car pull itself down from a straight, into a turn - you'll hear the engine going REVVvvv-REVvv-Revv. That's the driver doing what we've described. It's usually blowing flame in time with the engine wind-downs. Very neat stuff, and it's more-or-less safe to practice on the street.

Brandon

 

I thought when you you put the clutch in, nutruel, clutch out, rev, clutch in, whatever gear.. was called doubling clutching and not rev matching?

 

Yes, that's double clutching, and it's a complete waste of time. There's no need to operate the clutch more than once in a modern synchromesh gearbox. Heel-toeing does not require double-clutching and is much faster without it.

 

Extactly... Brandon... you are confused there.. don't tell him how to double clutch... lol

 

currious how is it that you double clutch cause i have always wondered that! and does it have real big advantages?

 

None whatsoever - it just looks cool Like NZC said, in a modern gearbox, it doesn't help much (if at all).

The heel-toeing is the important part.

1) Cruise in gear
2) clutch pedal in
3) gear out
4) blip throttle
5) gear in
(really, you're doing 3-5 all at the same time)
6) clutch pedal out

Brandon

 

DOUBLE CLUTCHING IS F'ING STUPID! DONT DO IT!


Rev matching on the other hand, can help your car. While cruising, if you want to go down a gear, just ...


1. Push in clutch
2. While the clutch is still disengaged from the flywheel, blip the gas some. This will speed up your engine speed to help match your transmission speed
3. Put the car in the lower gear and let off the clutch

Youll know when you do it right. Itll just feel very smooth.

 

Just to clarify, You dont have to blip the throttle while taking the shifter out of gear...or while its in "neutral"...or even when its in the lower gear. Just BE SURE TO DO IT WHILE THE CLUTCH IS DISENGAGED FROM THE FLYWHEEL


Have a nice day

 

adamlewis: TELL THAT TO CLASSIC FERRARI OWNERS That was a bit unnecessary.

Brandon

 

No...Im sorry...Double clutching is a bit unnecessary. Thats what the syncromeshes are for. Learn about a gear box and then come back

 

I know about gearboxes. It may be unnecessary, but it's not like it does any damage, now is it?

Brandon

 

Yeah .. actually it wears out your clutch and pressure plate faster.

 

No, but it makes your gearchange a whole lot slower than it needs to be. If you know about gearboxes, you’ll know that it’s completely unnecessary with a synchromesh gearbox (unlike a classic Ferarri gearbox...)

 

Yeah, because don't you know that whole 100 RPM speed differential over the space of a whole 60 milliseconds just wears so much, doesn't it?

Whatever, I don't feel like getting into a pissing match. If nothing else, someone here now knows what people are talking about when they mention double-clutching, and why that like from TF&F is SO stupid

Brandon

 

Any difference, is still a difference, is still wear on the clutch. As for the pressure plate...I guess you dont mind someone sitting in your car and repeatedly pushing on your clutch pedal when it doesnt need to be? Because thats all youre doing when double clutching.

 

There are 2 perspectives to consider here, both from a performance standpoint. We will leave everyday street driving out for the purposes of this discussion. Also note that my point really only pertains to downshifting.

Bob Bondurant make a very firm point in his book that, ultimately, the speed of a shift is far less important than the accuracy and smoothness of the shift. That means that if a double-clutched shift is slower, but at the same time, easier on the gearbox, then it is preferable.

For endurance racers, the longevity of the gearbox is easily more crucial than the very last tenth of a second. If it won't finish the race, who cares how fast you were? The gearbox in an RX7 is typically the weak link in the drivetrain, so care must be taken to preserve its life. Double-clutching may increase wear on the clutch components, but since the clutch isn't under a load during a downshift, any additional wear is minimal. Besides, the point has been made elsewhere in this forum, what is costlier to replace, the clutch or the gearbox? So for the endurance racer, and for overall longevity, double-clutching has some merit. Overall, the internal components will gain some "slow down" time, which allows easier engagement of each gear.

For sprint or drag racing, where every last tenth is important, then gearbox longevity will take a backseat to overall speed. That doesn't mean that you have to be ham-fisted with the shifter, just move the shift lever in a smooth, positive manner and don't force anything.

Porsche 911 gearboxes are rather hard on synchros when autocrossed or run open track. And while autocrossers generally will sacrifice any longevity for that extra tenth, many 911 drivers I know who open-track their cars, double-clutch their downshifts religiously. Price out a 911 transaxle rebuild and you will know why. So while synchromesh transmissions do not require double-clutching like some earlier vintage gearboxes do, the practice is not without merit in a modern performance arena. I wouldn't go so far as to call it "completely unnecessary".

See, a whole post w/o any yelling!!!

 

well if it slows you down then what is the point? i mean even if it saves just a little bit of your gear box! I mean if you are racing on a circuit i would race! not sit there and double clutch i would simly shift to beat the guy infront of me lol!
Just my
$0.0002

 

Wow. Reading this makes me realize that most folks today have 0 clue how to drive a stick. Till I replaced my clutch, it was throw it in neutral, and hit the brakes. Now, new clutch installed, downshifting is so easy. You have to just listem. Turn the radio off, and listed to what your car tells you to do. If you over revv a downshift, remember how hard you pushed in the pedal, and push in the gas a little softer next time. I am to the point now, if I am not trying to be fast, I can downshift w/o my passenger feeling a thing. Hit some country roads, use the techniques Vettekiller and No7Yet described, leave the CD's at home, and just drive. The best mod you could ever want to do, is to drive your car like you own it...correctly!!