Time and again I read about double clutching. What is it and when is it to be used?

Cheers

 

Here is a good article about that subject.

<a href="http://integra.vtec.net/driving/dclutch.html" target="_blank">Everything you want to know about double clutching</a>

You do not need to double clutch with your 993's transimission, but it does help to use the double clutching when the engine and transmission is extrememly cold on a extrememly cold day (pun intended), to eliminate extra wear to the syncros. (Since the transmission fluid haven't had time to warm up to proper operating viscosity yet)

 

Zumbera:

Double clutching is a pretty strange and maneuver. It goes something like this for a shift from fourth to third:

Depress clutch
Move shift lever from fourth to neutral
Release clutch
Depress Clutch / blip throttle
Move shift lever from neutral to third
Release clutch

As Robin points out double clutching isn’t really necessary in modern cars as the gear sets are in constant mesh. You can achieve the same results by heel and toeing and thereby matching engine revs with transmission speed.

Hank

 

I'll preface this by saying that while I heel & toe like crazy, double-clutching still feels totally alien & I can't do it!

I think the sequence you listed is slightly off, IMHO. The highlighted 'depress clutch', below, should be moved to *after* you blip the throttle, rather than before. Since the blip is supposed to be spinning up the input shaft, you have to have the crank & tranny input shaft connected. Pushing in the clutch would disconnect them and defeat the purpose, right?

===============================

Depress clutch
Move shift lever from fourth to neutral
Release clutch
***Depress Clutch /*** blip throttle
Move shift lever from neutral to third
Release clutch

 

Hi all

Hank, I'd agree with Robert, the way I was taught was you blipped with the clutch out.
(But then, you're a lot faster than me.)

Zumbera, I believe it's good practice to give the throttle a good blip while you shift down, whether you are heel & toing or not.

M in C

 

I guess you guys are right. I am going out to my car to go run some errands. I'll test out how I do it. I think you just taught me something.

Hank

 

[quote]Originally posted by Hank Cohn:
<strong>I guess you guys are right. I am going out to my car to go run some errands. I'll test out how I do it. I think you just taught me something.

Hank</strong><hr></blockquote>


No wonder you thought it didn't accomplish anything!

 

Hi Kim

[quote] is there any harm in double-clutching? Additional clutch wear? <hr></blockquote>

I've always heard it was just the opposite.

I've read that some racers will d/c even when they don't have to because it's a rhythm thing, and they often are in cars where they must d/c.

Oh yeah, a sequential box will break you of the d/c habit very quickly

M in C

 

Hank doesn't use a clutch when downshifting because he shifts so fast it isn't needed. The blip is given while the clutch is out, before you press it in for the second time.
Only harm in double clutching is that it is probably a tad slower and another thing you can mess up. Only time I double clutch is in my street car when it is cold, as Robin mentioned.

For guys like Mike and DJ that have raced Formula Fords and such, double clutching is/was a requirement. It is probably very hard to break themselves of that habit, and most likely they are just as fast as most single clutching guys.

Greg

 

[quote]Originally posted by Silver Bullet:
<strong>I can't help but double clutch while heel-toeing! I read where it wasn't necessary to do it so in our cars so I tried not to but I can't get the sequence right! I get out of sync. if I don't let out the clutch. And this is even if I do it very slowly....

That being said, is there any harm in double-clutching? Additional clutch wear?</strong><hr></blockquote>

Absolutely! you must be wearing clutch master/slave cylinder, release bearing, throttle mechanism additionally. If you get your double clutching absolutely right you may save a tiny bit of wear on the synchros. Of course, not using the clutch once you're moving will ensure you get it right, but you need to be very, very brave, or very, very rich !!

Beats me why this topic keeps appearing, its just not necessary on modern P-cars - matching revs to road speed on changes is a far better skill to acquire!

Cheers, Maurice

 

Got back from my own errand running, and played w. double-clutching as well.

It reminded me of a tip I give me own students about learning to heel & toe: start out w. just the heel.

Trying to learn to heel & toe while you're zooming towards a turn-in and braking is a losing proposition! It's much easier to isolate the blipping outside of the braking zone of a turn.

Do this: drive down the freeway at a constant speed, in some gear that'll put you at about 4,000 rpm. clutch in, blip to ~5,500 while downshifting, let the clutch out. See how close you came to matching revs. Note that you're not braking, you're not turning, you're just holding a constant speed down the freeway. Shift normally back up to the higher gear, and continue down the road at that same constant speed. Now try the clutch in/blip and downshift/clutch out sequence, and see if you did any better at matching revs. Repeat ad nauseum.

When you get comfortable matching revs at that speed and selection of gears, try a different speed & gear combination - say, 40 on a surface street from 3rd to 2nd (if your gearbox will support it). The lower gears tend to be more challenging, and the car will become more sensitive to small differences in engine/wheel speed.

Get this rev matching down *first*, then play w. adding a brake input while blipping later. This approach makes it much, much easier to learn! I had to remind myself of this approach when trying out double-clutching today. It's going to take me some more practice, though, for d/c. <img src="graemlins/c.gif" border="0" alt="[ouch]" />

 

{snip} - replied to myself instead of editing!

 

The point of double-clutching is to use the engine rather than the synchros to speed up internal transmission parts. So it is necessary to blip the throttle with the clutch out (engaged). Under that condition, the engine has a direct connection to the tranny input shaft and can be used to accelerate the components on the input side of the tranny to match those on the output side. Keep in mind, while the car is in neutral, the input and output shafts have no direct connection. By using the engine to increase the speed of the input shaft to that of the output shaft, theoretically, synchros are not necessary.

Here's the process if you were downshifting from 3rd to 2nd. )Only double-clutch when downshifting as it's unecessary when upshifting)

Depress clutch
Put shifter from 3rd into Neutral
Let the clutch out
Blip the throttle with clutch engaged. This will bring BOTH the engine and transmission input shaft up to the SAME speed.
Depress the clutch
Select 2nd gear
Let the clutch out.

(now try to do it smoothly and quickly..


I learned this technique driving a 1941 Dodge Power Wagon that had no synchros. Downshifting was impossible unless I double-clutched. Forcing the lever was always met with the sound of gears grinding since the input/output halves of the tranny were spinning at different speeds and there were no internal parts (synchros) to bring their speeds together.

I was taught it again at the Road Atlanta Racing School in 1989 because their 300ZX synchros were completely trashed.

It is not a process that comes naturally but once you get in the habit, like so many other things, it becomes second nature.

Double-clutching is not necessary with almost any modern transmission. However, it does reduce wear on synchros, and does not increase clutch wear if done properly. When you get it right, it's fun (o.k., maybe I'm a bit too enthusiastic about some things...)

Matt

 

Good Thread

Now here's a different question: When blipping the throttle while downshifting, do you:
1. Depress clutch / blip / downshift / release clutch
or
2. Depress clutch / downshift / blip / release clutch

I do #1 more often, but #2 makes matching rpm's easier, therefore I'm migrating to style #2 more.

Hope I explained this clearly

 

Oleg

Both (1&2) are single clutching.

I think the easiest way to explain d/c is "Shift into neutral, blip, then shift into the next gear".
(And by shifting into neutral, I mean letting the clutch out in neutral).

M

Sorry, misread the question. I think it doesn't matter, you're just trying to match the engine speed to the speed of the rest of the drivetrain.