what is double-declutching?

[nmlowe]

I've seen and heard the expression 'double-declutching' used quite a bit over the past year or so, I saw it printed in an article about the Austin Healey and Triumph TR3A in a motoring section of the local rag for the first time in months, today.
I realised that I have no idea what the term refers to. I have had conversations with people about driving, and they have mentioned it. I usually just nod and agree with what they are saying.
I've tried to think logically about what it could mean, but i still have no idea.

Does anyone know what double-declutching is?

[Terminator]

Topic was covered a couple of months ago in this thread...

www.pistonheads.com/gassing/topic.asp?t=8134&f=23&h=0&hw=declutch

[philshort]

Its probably been explained on here before, more often than not incorrectly, so I'll have a go! I'll probably get it wrong too, so feel free to shoot me down anyone.

It harks back to when synchromesh was not standard fitment to manual gearboxes, in order to make a smooth gearshift on on downward changes particularly.

You declutch (depress the clutch pedal) to allow you to move the box out of gear. In doing so the layshaft disengages and starts to slow. You need to adjust the speed of the layshaft relative the speed of the mainshaft to allow smooth engagment of a lower gear. Blipping the throttle while the clutch is disengaged has no effect on the layshaft speed, as it is disengaged, so you need to engage the clutch (release the clutch pedal) before blipping. Depress the clutch again now the revs (and layshaft speed) are up, and snicj in the lower gear. Release the clutch to take up the drive.

Got that? Again in summary:

Depress clutch, out of gear, release clutch, blip throttle, depress clutch, into gear, release clutch. Two separate clutch disengagements, so its double de-clutching.

[nmlowe]

so it's not a good thing then?
sounds like a lengthy process!

cheers!

[philshort]

I think its quicker to do than explain!

Shouldn't need it with a modern synchro box though. Wonder if it might help with getting reverse in a T55 box?

[tvradict]

I found it slow and quite hard to begin with, but with a little practice it's become second nature! Sometimes i do it without thinking about it! Give it a try! helps maintain a smooth and surprisingly quick rythum (sp?)

[.mark]

quote:
I found it slow and quite hard to begin with, but with a little practice it's become second nature! Sometimes i do it without thinking about it! Give it a try! helps maintain a smooth and surprisingly quick rythum (sp?)

Yea - and if your in a tunnel or unde a bridge it makes loads of noise!!!!

[go-go]

Second grade mastering is to blip the throttle and make the double declutch when braking. This technique is called "Toe and heel". This permits hard decelleration and no waste of time for gearchange, obviously, without SMG or similar gearboxes.

Brake, Depress clutch, out of gear, release clutch, brake, blip throttle, depress clutch, into gear, release clutch. Funny.