The joy of double-clutching

[kjb]

Hello,

Two months into owning "Little Red" I'm surprised by some things I've learned to enjoy, especially in the shifting department.

In the cars I've grown up driving, shifting has never been a source of either joy or dismay: it's something you do between gears. For the first month of 911 ownership, I didn't think much of it either. I learned that the 915 was a little slower than the average modern transmission, but that was about it.

Then came the day when I started practicing double-clutching on down-shifts. The joy of getting it right! My goal is to learn a heel-toe double-clutch downshift. Are there any masters out there?

In general, I feel like I own real car that gives me feedback when I do things right and when I do things wrong. Most modern cars do neither, in my opinion. Am I crazy?

two months and still smiling,

j

[91C2wrencher]

Even a bad day driving a Porsche is better than a good day at work.

9 years and still smiling...........

[JmuRiz]

Driving a new car is for sure not as much fun as an older car. Too many electronic safety devices on the new ones...and not enough feel.
Also practicing a double clutching technique is good for when your clutch starts to go. My synchros went recently on 1st and 3rd...and knowin how to do this saved me the embarassing "crunch" sound at an intersection

Nathan
PS: You aren't crazy, at least not that i know of

[kepperly]

For longivity double clutch on the up shift also. To really save wear and tear, only use your brakes when slowing down. Brakes are alot cheaper to rebuild than trannys and double clutch on upshifts to save the syncros.

Keith Epperly
Wichita, Kansas Regional Membership Chair
87 slant nose turbo look cabriolet

[kjb]

I didn't think the layshaft needed any help spinning faster on the upshifts?

[GrindingGears]

ok, so i can double clutch....at least I think i can...

clutch in, shift to nuetral, clutch out, blip the throtle, clutch in, shift, clutch out....

anyway, i have a couple questions:

1) How high should I rev the rpms on the blip?

2) What the hell is the point of double clutching? To keep the rpms up? Make shifting easier?

Thanks

-Grind

[Quicksilver]

Originally posted by GrindingGears
1) How high should I rev the rpms on the blip?

2) What the hell is the point of double clutching? To keep the rpms up? Make shifting easier?

Thanks

-Grind

Your ear will tell you. Example: when you shift from 3rd to 2nd your ear 'knows' how much the note of the engine will rise. That is how far you should blip.

Why double clutch? The syncros in th tranny are little clutches that get the gear assemblies to match speeds (faster or slower) before the gears will engage. When you double clutch you are getting the input shaft side of the gear train matched in speed to the output side before you try to engage. This can make the engagement very smooth, increase syncro life, and add a little smile with a job well done.

On a more practical note learning to match speeds can let you drive a car that is having problems. When I first moved to SoCal the slave cylinder on my car failed so I had no clutch at all. My car would start in gear so I was able to drive stop and go traffic for a week until the new slave cylinder arrived.


Wayne

[mwbaum]

I always double clutch on high rev downshifts ie in the twisties where you are between 2 and 3 frequently ....especially 3 -2 and also 4-3.....(2-1 I usually just wait until things slow down enough but on the rare occasion I need a quick 2-1 downshift I def double clutch also). With my 915 trans I like to lightly blip the throttle between upshifting from 1-2 to spin up the synchros....it shifts more quickly and with less difficulty that way. After a few tries it becomes second nature. Quicksilver's note about "using your ear" is exactly how I do it....match the sound...after a while you wont need to look at your tach at all....

[masraum]

I didn't think the layshaft needed any help spinning faster on the upshifts?

The purpose of doubleclutching then is to make sure everything is spinning at the same speed. I don't think it will speed things up as much as help get them slowed down and matched. It does make a difference that you can feel.

clutch in, shift to nuetral, clutch out, blip the throtle, clutch in, shift, clutch out....

anyway, i have a couple questions:

1) How high should I rev the rpms on the blip?

2) What the hell is the point of double clutching? To keep the rpms up? Make shifting easier?

Your technique is correct, but you don't have to let the clutch completely out the first time, only part of the way to engagement.

1. When you downshift from 3rd to 2nd at a given speed the rpms may go from 3200 to 4000. That is the difference that you need to duplicate when rev-matching to downshift. Generally it is by getting to know your gearing and then after a little time paying some attention you can do it by ear.

Here's some info that I posted somewhere else on the internet that some of you may or may not find interesting.

Heel-n-toe is primarily a procedure for downshifting during braking to be able to brake and shift at the same time. It is important to rev-match when doing heel-n-toe or you'll probably/eventually end up spinning.

Anytime you downshift you should rev-match whether you are double-clutching, heel-n-toe or just downshifting. Rev-matching reduces lots of stresses on the entire drivetrain (axles, tires, transmission, clutch, probably even the crank and bearings in the engine somewhat). Rev matching makes your driving much smoother. If you downshift and don't rev-match you can actually lockup your back tires if you are not careful.

Heel-n-toe is a method of downshifting during braking so that when you are done braking and are ready to accelerate again you will already be in the correct gear for best acceleration. Generally this is only necessary when racing, but is not a bad thing for regular driving.

Double-clutching's primary purpose is to shift a transmission that is not syncronized. When a tranny or single gear of a tranny like first is not syncronized the only way to get it into gear is to doubleclutch. This can be useful if you wear out your syncros but don't have money to rebuild the tranny. It might also make a car theft resistant. There is lots of debate as to whether there is any benefit in a modern syncronized tranny, but I do it anyway.

Clutchless shifting in 99% of cars is only valuable for limping home without having to call a tow truck if you can't get the clutch to disengage. Similar to an earlier poster I was on my way to an important engagement that was about 30 miles from home, pulled up to a toll station and the clutch pedal went to the floor. Well, I was only about 10 miles from home, but couldn't miss the appointment, so I drove the last 20 miles there and the 30 miles home without using the clutch. Once you get the hang of it, it isn't very hard, but it sucks if you have to come to a complete stop. It's primarily used in race cars with race trannies and race motors. Race motors have minimized rotational mass and so rev up and down very quickly, and race trannies usually have straight cut gears and special dog teeth designed for clutchless shifting. From what I understand in the hands of an experienced racer you can actually outshift a syncronized transmission, and even the modern F1 type trannies ala Ferrari (that was is hard for me to believe, but I saw telemetry in some magazine).

[svandamme]

double clutching also sounds cool to people that are neir the point where you do the fancy brake/shift cornering..at least it does if you've got it mastered

[Supergranule]

i don't normally double clutch on downshifts.
i usually do: clutch in, shift and blip the throttle at the same time, then clutch out. is it better to let the clutch out when you blip the throttle? i'll sometimes leave the shifter in neutral for a moment when downshifting, but keep the clutch down. either way, the shifts are just as smooth, but the way i normally do it is quicker. is it easier on the car to let the clutch out when matching revs?

[svandamme]

do your synchro's still work?
i think they would have to doing it this way?

[Supergranule]

by the way, that's not how i shift my 911.....its not quite ready to be driven....

[gduke]

I learned the heal & toe double-clutch this summer. I'm also a newbe. Eventhough my syncro's are new, shifting feels sooo smooth. When you blip the throttle to match speeds, the tranny slips into the lower gear so smoothly, that you could do it w/out clutching.

It also really helps if your peddles are close to the same hight. I drove an older 912 last weekend and the break ped. was alot higher than the throttle, making heal & toe not possible.

Hey, eventhough I can do it with ease, I'm no Hurrly Heywood, yet.

[ljonespwc]

In the many discussions I've had with people over the years about the subject, I'd estimate that 50% believe that "rev matching" is the same as "double-clutching". They just didn't know the correct term.

[GrindingGears]

thanks for the responses....

rev matching is the same as double-clutching right?

from what i just read above it seems to be the same idea. how are they different?

also,

"There is lots of debate as to whether there is any benefit in a modern syncronized tranny, but I do it anyway."

I've heard this too, how modern is modern? '83? or are we talking 1998-plus M5s?

[stuartj]

Double clutching is slow, and possibly even dangerous when you are pressing on. Its only application, IMHO, is when changing to first on the move.

Heel/toe is an essential skill and if you cant do it, you cant truly exploit the potential of a 911 or any other sports car. Its also kind to the car on an every day basis. Just my MHO ofcourse.

stuart 87 carrerra

[jazzbass]

Originally posted by stuartj
Double clutching is slow

In my car, its actually faster because I don't have to wait for the synchronizers. Still fine tuning the technique, but man - when you hit it right - nothing smoother or faster. Granted, my 915 can be, lets say, *difficult*, so YMMV.

[stuartj]

I am surprised that clutch/disengage/declutch/clutch/engage/declutch can be faster than a well executed heel/toe downchange which is just one fluid "blip". And as this usually occurs while braking hard and setting up for a corner, it would seem to fit the driver's maxim "give yourself the least number of things to do" -double clutching doesnt.

Certainly isnt quicker on my 915 clunk box, you must spend more time in the gym doing leg presses than me

As you say, YMMV.

stuart 87 carrera

[Victor]

StuartJ, the last guy who had his head under the drivers side of your dashboard told me you have a spurt-o-matic. Or was he talking about something else?