double de clutching... Good or bad?

[crazyj]

Hi,

I was 'pressing on' a little the other day and on exiting my favourite deserted roundabout......I changed down for the exit and I found my self double declutching...

Felt nice... Nostalgic... plus the yeti zipped along like a good un.

But I thought... Are these kind of clutch shenanigans good or BAD for the modern and terribly brittle/consumable Dual mass flywheel things?

Any ideas?

J

[devonutopia]

I often do rev matching as shifting feels better on downshifts.  Can't say I ever double declutch though.  Not something I actually have ever learned to do.  (A pitfall of driving a relatively short period of time?)

[Toxicvrs]

I will if in a classic, nothing else though

[Urrell]

As I posted earlier today:  http://www.briskoda.net/forums/topic/333994-dmf-flywheel/?p=4074831

[crazyj]

Thanks guys... Had missed the post earlier.

Something of a hot topic!

I have found that things that feel good or are fun are seldom good for us... or our machines... Nice to find an exception.

Cheers

J

[bubba]

When I was on my advanced driving course in 2007, it was taught to us, however in the last few years, they've stopped teaching it.

It doesn't help that most of our advanced cars are automatics!

[Brijo]

Some of us learned to drive in the era of non-synchro first gear.  Double-declutch going down - or blush at the noisily demonstrated incompetence.....

 

And with a three-speed box (really!), first gear was not just for moving off. 

 

Grief!  I do feel old sometimes. 

[Ryeman]

If the synchros are not forced to do any work your trans incl clutch will effectively never wear out and be 'bliss' for a DMF.

For me it's THE joy of a manual........that's how old I am, brings back memories of the old Ford tanker side-valve V8 and 'crash box'.

[rustic]

Double de clutching is just wearing out the moving clutch parts twice as fast for no other gain.

Puts extra wear and tear on your left knee too.

Takes longer to complete a gear change and slows progress, not healthy if you have just pulled out into moving traffic.

Far better to rev match up and down, much kinder to clutches and the transmission.

If you cause a snatch when changing gear, you are doing it wrong, increasing wear, and damaging the DMF, bringing an expensive repair closer.

If you want to see how well you can rev match, you could try gear changing without using the clutch... Aghhhh....

Warning.... Do not try this at home with your own car... expensive wear and tear can follow if done incorrectly...

Best tried on a test track prior to it's last trip to the scrap yard.

I wonder how modern cars cope with learner drivers with kangaroo starts... and engine stalls, not good for DMFs.

[weasley]

I occasionally double de-clutch, usually if I am pushing on, making a block down-shift and want the gearbox and clutch all lined up at the higher revs; it gives the synchro a bit of an easier time. It makes virtually no difference to the clutch; yes you are operating the release bearing more often but you are also saving the clutch plate from slipping. I learnt it through necessity when the synchros on my first car (1977 Mini) wore out and have subsequently used it to good effect in trucks. Also a useful technique if your clutch hydraulics/cable fail and you wish to try and get somewhere using clutchless shifts.

Effect on the DMF? I would suspect it is marginal. Double de-clutching puts very little load or stress on the clutch plate and flywheel and (if done properly) no shock loads, which is what tends to do for DMFs.

[Ryeman]

What a nightmare it was replacing the carbon thrust ring on the Austin 1800.

[crazyj]

My First car was a 1963 series IIa 2 1/4 landrover diesel. No synchro between first and second!

Loved it.

Such fun!

Cheers

J

[freedie]

Some of us learned to drive in the era of non-synchro first gear.  Double-declutch going down - or blush at the noisily demonstrated incompetence.....

 

And with a three-speed box (really!), first gear was not just for moving off. 

 

Grief!  I do feel old sometimes. 

 

Can't find it? Grind it!

[Ryeman]

There won't be such a thing as 'driving' before much longer, the way things are going.

[Gyp]

What I'm struggling with is wondering why to double declutch, rather than simply matching revs during the change - ie why let the clutch out mid change?

[33q]

When driving a manual I always match the revs....as the IAM used to term it....a sustained change.

It is very satisfying to work sympathetically with any machinery .... I know I'm a sad boring old git....but proud of it

Many people these days have no understanding of the mechanisms they are operating and through this ignorance they cause premature wear or damage. In turn this can be costly and be less safe.....but if someone else is picking up the bill...they don't care

[weasley]

What I'm struggling with is wondering why to double declutch, rather than simply matching revs during the change - ie why let the clutch out mid change?

Rev matching is good for vehicle stability and clutch wear prevention... I do this as a matter of course (often with heel/toe if I am braking too, although I find the Yeti pedals not ideally placed for this).

Double de-clutching has little benefit in a synchromeshed gearbox, but what it does is speed up the gearbox shaft for the gear you are about to select, so that the dog clutch on the shaft can lock the gear with little or no effort. You are effectively using the engine to get the gearbox synchronised, rather than letting the synchro cones do it. In olden days there were no synchros so it was a necessity, particularly for down-shifts.

If I am block down-shifting (eg 4th to 2nd) then I know that the synchro on 2nd will get a bashing due to the large mismatch of revs inside the 'box. In truth, the synchro is well able to deal with it, but it does baulk the shift whilst the synchro does its thing. By double de-clutching I can slot the 'box into 2nd with no resistance and with an inward smile of satisfaction.

Equally, if block-shifting up the 'box I will pause before taking the higher gear to give the shaft in the gearbox time to slow down to a matching speed. No need for a double de-clutch as the revs will drop naturally anyway.

Finally, whilst we're on gearbox sympathy, when stationary in neutral, I will push the clutch.... pause.... then take 1st or reverse. This gives the input shaft time to come to a stop before selecting the gear. On cars with no synchronised reverse, this prevents that awful crunch you hear so much in supermarket car parks.

[Urrell]

What I'm struggling with is wondering why to double declutch, rather than simply matching revs during the change - ie why let the clutch out mid change?

To bring the clutch plate to the same speed as the engine/gearbox combo so the gear will just drop in rather than the syncro cones having to do it.

I took my class 1 HGV test in a Leyland Chieftain, no syncro on any gear but silky smooth if done right.

I have never had a replacement clutch fitted to any of my veichles including a Fiesta XR2 that I did 130,000 miles in and that was driven anything but lightly/

[g6zru]

Double de-clutching? I doubt if it's ever necessary with todays cars but I also doubt it being harmful. My philosophy in all things nowadays is if it feels good do it! :cocktail:     

 

Fred

[Urrell]

Double de-clutching? I doubt if it's ever necessary with todays cars but I also doubt it being harmful.

 

Fred

Exactly, and very difficult to do at normal speeds with todays light transmissions. But it works well when pressing on with toe and heeling

[meb90]

Finally, whilst we're on gearbox sympathy, when stationary in neutral, I will push the clutch.... pause.... then take 1st or reverse. This gives the input shaft time to come to a stop before selecting the gear. On cars with no synchronised reverse, this prevents that awful crunch you hear so much in supermarket car parks.

 

That'll explain the crunch I get! Hadn't realised it may be due to having no synchro (in the Fiesta). Thanks!

[countryboy]

If done properly it will do more good than harm, I learnt to double declutch on old Ford tractors in the 70's and 80's. They had no synchro whatsoever and unless you did it properly any down change on the road only ended up with you playing tunes on the gearbox. The only components that will get a harder time is the operating mechanism as if you are double declutching rather then just blipping the throttle on the downchange then they are used twice as much. If I am coming to a junction or roundabout in top gear then I will always block change down to 4th and then 2nd if I need to using the heel and toe and double declutching technique. It makes for a smoother drive and give the synchro cones on those gears a much easier time.

 

Ian

[jonceebee]

I used to double declutch going down to first gear on my first car, a three speed side valve 100E Ford Anglia, don't I have never done it since. Do you remember those vacuum windscreen wipers, especially uphill !

[littleade]

With modern gearboxes there is no need due to syncromesh so why do it? Double de-clutching means you will be free wheeling in neutral, which is bad practice IMO.

[Brijo]

I used to double declutch going down to first gear on my first car, a three speed side valve 100E Ford Anglia, don't I have never done it since. Do you remember those vacuum windscreen wipers, especially uphill !

That's the baby!  The last car I de-coked.