Double de-clutching

[monkey11477]

I was told this is only really any good on down shifts where you;

depress the clutch and take it out of gear
release clutch
match revs to roadspeed of intended gear
depress clutch select gear then release.

i've never understood why you just can't hold the clutch in from the point you take it out of gear untill you have the new gear selected and the revs matched as this is what I do

[Don]

We reallyMUST do a Wiki with full definitions of "double de-clutch" and "heel and toe" and "left foot braking" and "threshold braking" and so on.

In answer: there is no need to double de-clutch in a modern car with a modern synchmesh gearbox. No need at all.

[monkey11477]

I know this Don, I was taught double declutching on a modern car and when I questioned it all I got was a mumble about car balance.

Surely there is a benefit of matching revs to roadspeed when selecting a lower gear synchromesh or not.

My original question stands

[stefan1]

I think you are violently agreeing. You can, as you say in your first post, match revs on downchange with a single declutch action.

Double declutching just has the additional "benefit" of negating the need for the synchro.

Personally, I both single and double declutch depending on the car, my desired speed of change and what I feel like doing!

But, to be clear, you do not need to double declutch to match engine revs.

Kind regards

Steve

[Pigeon]

I've double-declutched loads of what I'd call "modern" cars, usually because they're old heaps with a knackered synchro on second, but sometimes because they're new and built with a crap gearbox. Quick lift-and-blip vs. hnnngh into second feeling like something's being overstrained... it feels good it's still a useful technique to know because you can't guarantee that every car you drive will be in mechanically perfect condition, especially if it's not yours, and it makes me glad to have learnt to drive in a Morris Minor

[Don]

Stefan's right. No need to double de-clutch. And you can rev match on downchanges with only one de-clutch,rev-match, clutch action.

Pigeon is also right that if you drive and old classic (or junker!) or car with a knackered gearbox it's handy to know how to do it - even if for 99% of one's driving career it's irrelevant.

As to "benefits" of double de-clutch in a modern syncromesh car? Can't think of any - it just makes gear changes longer!

[RT106]

I double de-clutch my vaguely modern Mondeo when it's cold because the synchros don't work perfectly until the gearbox oil is warm. It'll go into gear without DDC, but the change is smoother with. I also find that DDC results in a smoother 5th to 4th change at motorway speeds, but that's probably more to do with me being an inept fool than anything mechanical.

In my 205 GTi double de-clutching is the only way to downchange into 3rd, but that's just because the box is f*cked.

I think it's a useful technique to have and doesn't have any tangible disadvantages.

[balls-out]

Don said:

Stefan's right. No need to double de-clutch. And you can rev match on downchanges with only one de-clutch,rev-match, clutch action.

Pigeon is also right that if you drive and old classic (or junker!) or car with a knackered gearbox it's handy to know how to do it - even if for 99% of one's driving career it's irrelevant.

As to "benefits" of double de-clutch in a modern syncromesh car? Can't think of any - it just makes gear changes longer!

Depends what you mean by a modern car. if you mean a new car, then yes you are right (but its fun). If you mean a car modern enough to have syncro, then not necessarily, If owned cars that have syncro, but well past its best (2nd is usually the first to go) and double-dc makes things smoother and lengthens what life is left in the gearbox.

[Holst]

My car has a damaged 5th gear syncro and I have to DDC to get it to change smoothly. If i just push it in it makes a loud clunk, and at higher speeds it wont happily change upto 5th at all.

Ive got so used to DDC into 5th that i do it automatically and its not any slower than using the syncro for a smooth change. I even DDC in other cars as its become an automatic thing.. 5th gear DDC.

One day I will rebuild the box and probably forget how to DDC.

[Adom]

I find i get a satisfaction from getting it spot on...doesn't happen every time but you know when you do because it almost 'sucks' it into gear. (fnarr)

Also much better on cold gearboxes (and pretty much a necessity to get it into 2nd on my old renault 5). my brothers and i do it on every down-change so its totally second nature and negligably slower than not ddc.

There are no downsides!! saying that I totally agree that its not needed on modern stuff and will make no diff to balance etc etc.....but then for me, cars/driving have very little to do with 'need'

[GreenV8S]

Holst said:

Ive got so used to DDC into 5th that i do it automatically

Unless you're changing down from sixth, I don't understand why that would need DDC. Even cars with no synchro at all will usually snick up through the 'box without DDC.

[Holst]

GreenV8S said:

Holst said:

Ive got so used to DDC into 5th that i do it automatically

Unless you're changing down from sixth, I don't understand why that would need DDC. Even cars with no synchro at all will usually snick up through the 'box without DDC.

When your syncro is damaged I think it might be worse than a box without syncros at all. Although i must admit that ive never driven a car without!

Its not that it wont go into 5th at all but its much quicker to DDC up into 5th than to wait for the box to slow enough that it will go in smoothly. At lower revs DDC isnt needed, but at higher revs it helps alot. If I didnt need to do it I wouldnt bother, but in my car it makes a big difference especially when "making progress"

EDIT - I dont have a 6th gear, so i only use it on upshift.

Edited by Holst on Tuesday 19th February 19:25

[SVS]

RT106 said:

I think it's a useful technique to have and doesn't have any tangible disadvantages.

... except that it can wear out the pivot on your clutch, as has happened to me. I've since given up DDC and find single-clutch, sustained revs changes perfectly smooth.

[WhoseGeneration]

Ok, who will admit to DDC on an upchange?.

[Vipers]

WhoseGeneration said:

Ok, who will admit to DDC on an upchange?.

I can recall some elderly gentlemen doing this back in the 60's in military vehicles, (civilian drivers), so I assume you had to do this as well with the old crash boxe's, any idea if this was the case?.

Personally, I learnt to drive in a Bedford RL (3 tonner), and we had to DDC on the downshift, cant recall doing it on the upshift, (also had to do this in the Land Rovers (talking around 69, )and for years continued to do this in cars downshifting from 4 to 3, I always found this a very smooth operation

[vonhosen]

WhoseGeneration said:

Ok, who will admit to DDC on an upchange?.

If practicing.

[falcemob]

WhoseGeneration said:

Ok, who will admit to DDC on an upchange?.

I do on my Disco going from 1st to 2nd and back down as well.
DDCing on a properly working synchromesh box does no good at all and can cause damage.
Anyone who thinks they are expert at double de-clutching should change gear without using the clutch to see how good they really are.

[WhoseGeneration]

vonhosen said:

WhoseGeneration said:

Ok, who will admit to DDC on an upchange?.

If practicing.

Yup, I'll admit to it on occasions too.
As you say, practise, more tools in the box.
Then, it can be a way to help others to achieve a smooth change.
Slow it down first.
"Don't snatch the gears".
Or, make them drive in their socks.

[944Nick]

There's a small benefit in double declutching on both up and down-changes, in that the action of increasing* revs while the clutch is engaged spins up the input shaft in the gearbox to the speed which it'll be doing when the gear is engaged. This saves the synchromesh having to do that job and also reduces the need for the car's momentum to increase the shaft's speed, which can make the change fractionally smoother.

It's also kinder to the synchromesh, as Stefan says.

As several others have mentioned, it's a nice tool to have in the box for those occasions when it can offer an, admittedly small, benefit.

• As well as for donwchanges, it can help in situations where you're upchanging and the release of the clutch allows the input shaft's speed to drop below what it will be with the new (higher) gear engaged.

In my 18-odd year old 944, it certainly helps the synchromesh out when going from first to second gear with cold gearbox oil. It's also worked under similar circumstances for a colleague who had a fairly new Honda S2000.

regards
Nick

[WilliBetz]

WhoseGeneration said:

Ok, who will admit to DDC on an upchange?.

Only in cars with manual gearboxes.