double clutching, yes I am an idiot

[lendaddy]

Ok, I'll take the fall for all us tools.

What the heck is double clutching? You can't mean clutch/remove from grear to neutral/releaseclutch/re-engage clutch/ place in next gear/release clutch. Can you? please someone give a step by step process. Thanks.

[masraum]

lendaddy, see you are an expert!

That is exactly double-clutching, but you only have to let the clutch out about half way in the middle process, just a little flex of the calf.

If you are upshifting you don't blip the throttle, but if you are downshifting you do blip the throttle.

[Boss]

You actually have it right in your post. The idea is to spin up the g/box input shaft to the rpm where it is syncronized with the road speed in the lower gear you are going to engage. The idea is to lessen the work the syncomesh has to do (or keep the dog teeth from grinding if your synchromesh is worn out).
If you properly match revs on a down shift but don't double clutch, the synchromesh still has to speed up the input shaft and associated parts.

Hope this is somewhat clear.

[morstad]

Double clutching is used only for down shifting where you push in the clutch put the car in neutral remove the clutch blip the throttle to keep RPM's up then engage the clutch and move it into the lower gear. If done effectively you can reduce wear on your synchros by matching flywheel speed with transmission speed. (As I understand)

[RallyJon]

You're forgetting the throttle blip with the clutch out in neutral to bring the layshaft up to speed.

Um, assuming that 911's have a layshaft...

1) clutch in
2) shift to neutral
3) clutch out
4) blip throttle to get layshaft up to speed
5) clutch in
6) select lower gear
7) blip throttle to get engine up to speed
8) clutch out
9) throttle in

You can do 6 and 7 at once, but there are two distinct throttle blips.

[jhugh]

If you just go out and practice it - yes, even with heel & toe braking on downshifts - you'll get it pretty quickly. I do it on every downshift now, just as a matter of habit. Soooooo much better on the trans.

It's easier to be movitated to do it once you've paid for a trans rebuild, believe me.

Cheers,

[pbs911]

What if you have a lightened flywheel? it doesn't seem that double clutching would work due to the motor winding down so quickly. In that case you would have to do the heal to toe, right?

[Jamie79SC]

Rather than 'blip' the throttle, press the throttle to match the revs. 'Blipping' isn't precise enough. It takes practice, but it's so nice when it works.

I have a lightened clutch plate, so unless I'm really flogging it, there are even times when I give her a tiny bit of throttle in the middle of upshifts.

[lendaddy]

Wow, that just seems aweful slow. But after racing motocross you take quick shifting for granted I guess. I have tried the above process and saw little to no decrease in the crunch factor. Maybe my tranny was already too far gone?

[APKhaos]

There was a longish thread on this subject last year - a search on double clutching should find it.

Double clutching was [is] essential for racing gearboxes with straight cut teeth and no synchromesh. There was no alternative.

A synchromesh gearbox does not require the double clutch downshift, but does benefit greatly from rev matching on the downshift - the classic heel & toe downshift. Getting the rev matching right gets you 80% of the benefit with one cycle of the clutch. The extra cycle of the clutch in a double clutch process gain very little extra benefit - the synchromesh is still used, and has about the same amount of work to do.

Rev matching the downshift, whether as part of a heel & toe technique or not [ie, independent of braking technique] ensures that the drivetrain is not loaded up by having to spin the engine up [or down] when the clutch is engaged. The car stays balanced.

[ricwon]

steve mcqueen used that technique in bullit. i think his mustang must have had the 5-sp with all of the upshifting he did to get his car up to speed. cool movie tho.

[BGCarrera32]

Wow, that just seems aweful slow.

Yeah, I don't think "blipping" is quite the right word when using a 915 transmission anyway. I can't do the cycle nearly as quick as I can in my Civic Si. But that's not to say that it doesn't make sense. Its just that the 915 in most cases isn't a speedy shifting device.

I agree that actually holding the throttle at the desired rpm would be a more accurate description.

-BG

[ChrisBennet]

Double clutching isn't necessary with a Porsche (syncromesh) transmission unless the syncros are worn out. Just blip the throttle during your downshift to match revs before engagement.

"Blipping" is the usual technique with a stock 911 due to the pedal arrangement. You can hold the throttle at the desired RPM with your foot but if you are braking at the same time you can only reach the (stock) gas pedal with the heel of your foot - at the bottom of the gas pedal near the floor. When you are pressing the gas pedal a couple of inches from the floor you have limited feel so you use more of a ballistic "stab" with the heel instead of a "press".

-Chris