Double Clutching... Question

[RJ Gilliam]

Ok, so this gentleman comes up from down south to test drive my car for possible purchase. He is a Porsche owner so I think, no big deal.

I take the guy for a little spirted drive down a straight away to give him the pull of the turbo, then I get out and let him drive, well when he shifts gears, he double clutched. I was going to ask him why but did not want to seem like an idiot. I thought the only reason for double clutching was the alighnment of the syncros, and with the newer technology that this was not needed.

Can someone please give me the reason you should or should not double clutch when driving?

[Joeaksa]

Rich,

Its still easier on any gearbox to double clutch, especially on the downshifts. I do it all the time but am used to it. While the syncro's do not "require" it anymore it still helps...

Joe

[RJ Gilliam]

Thanks Joe...

p.s. Julie was not happy with someone else driving her, she has not spoken to me all night....

[Joeaksa]

RJ,

You should have given me a chance first! Bet she will be mad for a long time and you deserve it!

Joe

[jwetering]

Four reasons to double clutch...I assume you are talking about the downshifts...

1) Save wear on the synchros. Their job is to match the speed of the output shaft to the speed of the gear, but they wear out in the process.

2) Faster downshifts. Those 915 synchros can be notoriously slow to react, and will balk if you push them too fast. Rev matched downshifts (achieved by double clutching) eliminates the need for them to work at all.

3) Smoother downshifts. When you let the clutch out without matching revs the drivetrain "lurches" as all the gears spin up to the same speed. If you do this anywhere near a corner say, this lurching will unbalance the car and could easily spin you off into the weeds. I learned this the hard way in my youth when I put a fresh clutch in my BMW.

4) Wear on the clutch. If you don't match the revs of the output shaft and gears, you clutch will have to do the work.

There you go - double clutching will give all four benefits.
Rev matching alone, will achieve the last three benefits.
Heel and toe downshifts (search the archives) will let you double clutch while braking.

Like many on this board - I can't not do these things when I drive. It becomes second nature.

[McDaniel]

Some of us are so ancient that we learned to drive when Porsche's and other sporting type cars had 'crash' gear boxes.
Once learned, it becomes habit, and as listed above, there are
many benifits.

[motion]

What the heck is double clutching?

[MarkP]

Can some one walk us through the steps? I was having a real hard time yesterday at DE with my down shifts, under heavy breaking, just prior to turn in. Just couldn't get it through the gate from 4th to 3rd - I have a 901 transmission.

Step 1 - Brake, clutch in
Step 2 - ???? help

[turbo6bar]

What about upshifting? I've noticed the gearbox is easier to engage when I try to match the revs to the next gear. I find the revs drop too quickly, because I tend to be slow and deliberate with the shifter. So, I'll keep my foot on the gas, but let the revs drop a thousand or 1500.

These Porsches require a true finesse, for lack of a better word.

Jurgen

[HawgRyder]

Procedure for double-clutching (short version for down-shifting).
To decelerate ....
Foot off gas
Clutch in
Shift to neutral
Clutch out
Rev engine to desired RPM
Clutch in
Shift to lower gear
Clutch out
Foot off gas
Try not to bounce head off steering wheel (if engine has lots of compression) LOL
I was watching Hans Stuck yesterday on Speed channel....his shifts were, to say the least, amazingly fast.
All this work happens in less than 1/2 second if done correctly (I'm still trying to get it smooth and fast after 40 years of doing it).
Bob

[MarkP]

Thanks Bob, I will be practicing!

[power]

I used to drive truck in my mis-spent youth, among other things, I found out it's manditory to rev match engine and transmission. Learning is a little difficult at first, you had to watch the tachometer very closely (careful: It's easy to over rev, a quick revining car engine when in nuetral) to get a feel for the correct rpm & gear combination. Once you found the appropriate combinations (compensating for load, vehicle speed, ect..) you could go by feel/engine noise, and it became automatic. Race drivers become experts at this, and set up cars so they can easily heel-toe on downshift (I only occasionaly heel-toe during spirited driving, as it is a little difficult without proper pedal set-up) I was always curious why people were never taught to rev match on manual transmission vehicles. People used to know how before synchromesh. I suspect an evil plot by clutch manufacturer's............

[Eric Coffey]

Here's my (heel/toe) method:

#1. Apply brakes! (nail your braking point first).
#2. Clutch in.
#3. Downshift (no stopping off at neutral).
#4. Blip throttle.
#5. Clutch out.

#2-#5 is one fluid movement.

Yes, this isn't the "true" double-clutch downshift/ heel-toe method, as it uses (takes advantage of) the synchros. However, it is much faster and less complicated (read: harder to foul up or miss a shift) IMO. The only difference is that you have to give a slightly heavier blip to match revs. You will find that many racing drivers also employ this same technique. If that isn't an option because of a worn gearbox, a straight-cut dog box, or just synchro wear paranoia, then you use the normal method:

clutch in, shift to neutral, clutch out, blip throttle, clutch in, shift to lower gear, clutch out.

You can usually just dip the clutch in and out of neutral (with a throttle blip in the middle) on your way to the lower gear.



DISCLAIMER: This is just one guy's opinion and method of doing things. For entertainment purposes only. Professional driver on a closed course. Yada Yada Yada.

[Superman]

Just keep your foot on the gas, if downshifting. Simpler and the throttle's already 'blipped.' So, the steps are fewer. Tap the clutch (engine will rev, but it needs to anyway, in order to downshift) and shift to neutral. As you're shifting into the lower gear, tap the clutch again. When the gears are meshing properly, the clutch won't need as much depressing. When done right, double clutching can be little more than one to two brief taps of the pedal.

Really, to get the full sense of how smooth this maneuver can be, drive an old truck and try not to use the clutch at all. Once you're moving it can be pretty easy to just slip into an out of gears buy just finding the right engine speed. Double-clutching is really done with the gas pedal, and it seeks to reduce clutch pedal use, and especially clutch pedal travel.

[Lothar]

I was watching Sasha Massen (spelling?) in one of the GT Porsches at Le Mans last year. They had a great in car camera of the foot well. It was amazing!!! He was heel&toeing down throught the gears as he would enter the tight turns.

Question: Why did he go through each gear on the way down? It looked like he was downshifting from 4th to 2nd or 5th to 3rd.

What I thought i was seeing was:

brake on
clutch in
right foot blip throttle
clutch out.
repeat for next gear down

the motion was fluid and smooth but blazing fast.

[dhoward]

Originally posted by Lothar
I was watching Sasha Massen (spelling?) in one of the GT Porsches at Le Mans last year. ...
Question: Why did he go through each gear on the way down? It looked like he was downshifting from 4th to 2nd or 5th to 3rd.

Sequential gearbox?

[Lothar]

I don't think that car had sequential. If it did, would it still require engaging the clutch on each shift?

[Langers]

Where it gets really complicated is when you are driving an old car with dodgy syncros and have to brake at the same time:

1) foot on brake
2) clutch in
3) change to netural
4) clutch out
5) blip throttle, with foot still on brake, to spin up layshaft
6) clutch in
7) move to lower gear
8) blip throttle to get flywheel to match clutch speed
9) clutch out
10) off gas and back on throttle...

[47silver]

double clutching on the downshift is like a zen thing when you feel the engine rpm match the speed of the transmission and axles.

learn to use the heel/toe method in order to down shift when slowing down and especially prior to entering a turn with a little gusto.

imho

[McDaniel]

I learned back in my racing days...brakes cost less than transmissions. Use the binders along with the downshift