Double de-clutching

[Winter]

Apropos a related topic on clutch wear, many years ago I was taught always to do this and of course heel-and-toe - although in my V8 the latter is done by the sole of my shoe straddling both brake pedal and accelerator.

This makes for smooth changes irrespective of speed.

Jackie Stewart used to give the following tip: there should be no abrupt movement during the process and a passenger for instance should be able to tell that gears were being changed only by engine tone. Clutches last longer and there is no horrible whine as flywheel and driven plate catch up with each other.

Synchromesh is a red herring, it doesn't address flywheel/clutch plate equalisation.

Mind you, with fuel prices as they are, excess fuel used would probably cost more than the replacement of even expensive V8 clutches.

Any thoughts?

[Tentenths]

The benefits of double de-clutching were instilled into me by my father when he taught to me drive many years ago; a habit I've maintained to this day. It may no longer be considered best practice but in my experience it makes for smoother gearchanges and definitely extends clutch life. The original clutch on my current Subaru lasted 180,000 miles, and the previous Legacy still had its first clutch when it was p'xd at 186,000 miles. Turbocharged, 220+ bhp, full time 4wd and hard driven in both cases.

[Winter]

The benefits of double de-clutching were instilled into me by my father when he taught to me drive many years ago; a habit I've maintained to this day. It may no longer be considered best practice but in my experience it makes for smoother gearchanges and definitely extends clutch life. The original clutch on my current Subaru lasted 180,000 miles, and the previous Legacy still had its first clutch when it was p'xd at 186,000 miles. Turbocharged, 220+ bhp, full time 4wd and hard driven in both cases.

Absolutely.

In some forty years' motoring, I have never had a worn clutch. Whenever I have done a major engine overhaul, simply as a matter of course, I replace a clutch on the grounds of while-I'm-here-I-might-as-well-do-it.

Recently I had clutch judder. The clutch had done 63,000 miles so on the basis of LEW posts that suggested a life of about 20,000 - 25,000 miles I thought it had done pretty well. Dismantling revealed little worn plates but dry splines. There was still loads of life in the unit.

Suitable lubricant was all that was required - even so, I still had a new clutch put in.

Incidentally, I kept the old one and in due course I intend to have the plates refurbished by PNM.

[Kimbers]

I Agree. Never do it with my Honda's as they have superb clutches (and I only have them for 3 months)

[MPx]

I agree .... but still dont do it... indeed jealous of those who can. Have tried to master heel and toe for years but have to admit I'm crap at it. If I ignore braking I'm pretty good at using the throttle to equalise wheel/engine speed to the point where I can do clutchless changes if I want....and I dont have a history of worn clutches or gearboxes despite long ownership periods and including trackdays. BUT...in a fast driving situation when you need to brake and change down together (heal and toe), it seems I either get the braking right and either over or under rev, or I get the revs right and either dont stop or stand it on its nose. As a result, in normal driving I tend to change speed using the throttle/engine rather than the brakes - smooth and relaxed, but not really very fast!! So am I just a confirmed single tasker or could I do something more about it. Any pointers appreciated.

Mike

Edited February 8, 2008 by MPx

[Quicker]

The following is a beginner's approach to learning how to double - clutch. This technique allows downshifts from higher speeds without any synchroniser wear. This is VERY important if you ever want to drive really quickly and keep your transmission intact for extended periods!

The Easy Way to Double-Clutch

By Jeff Krause.

Double-clutching is the proper way to downshift at speed without placing excessive wear on the transmission's synchronizers. This allows you to select a much lower gear without the tell-tale lurch you normally get when the clutch is let out after downshifting.

When downshifting my BMW M5 from 4th gear to 2nd at 50 mph, I need to raise the engine speed from 2200 rpm to 5000. To prevent excessive synchroniser wear, the clutch is depressed and the shifter is moved to neutral. The clutch is then released, and the gas is depressed to bring the engine speed up to where it needs to be for the lower gear. The clutch is then depressed again and the shift lever moved into the lower gear. When the clutch is released the second time, the engine is already turning the proper speed . While this sounds complicated, it's easier done than said, and only takes about a second.

To better understand how the process works, a little background on transmission fundamentals will help.

A typical transmisson has two shafts, one connected to the engine through the clutch, and one connected to the rear wheels. There are usually four to six sets of gears on these shafts and they are selected with the gearshift lever inside the car. When changing gears, the clutch is depressed to disconnect the engine from the transmission so there isn't any stress on the moving parts. Since the output shaft is permanently connected to the rear wheels, the only way to match the speed of the two shafts is to use the throttle to adjust engine speed.

Once the engine is turning the right rpm, both shafts will be turning the same speed, and the gear lever will fall into gear WITHOUT using the clutch! (Although most of the time you are shifting too fast to be that accurate)

EXCERCISES

1) With the car idling in neutral, slowly step on the gas until the engine is turning 3500 rpm. Do it again bringing the rpm's up more and more quickly until you can give the pedal a quick stab and have the revs stop where you want . As you shorten the time allowed to match revs, you will notice it takes more throttle. In fast driving, you will be shifting so fast 4 will take full thottle! Now try matching revs at 4000 rpm.

2) Find a deserted road, and maintain 40 mph in 4th gear. Now shift into 3rd, and see how many rpm's the engine speed increased. At this speed, the difference won't be very much - maybe only a few hundred rpm. Go back into 4th gear. This time put the clutch in, push the lever to neutral and let the clutch back out. You are now coasting with the clutch out. Raise the engine speed to where it will be in third gear. Quickly push the clutch in, select 3rd gear, and let the clutch out. There should be no perceptible lurch if you accurately matched revs. Try the same thing at higher and higher speeds. As the road speed goes up, the speed difference between gears will go up as well. When going from 5th to 3rd a highway speeds, you may end up within 1000 rpm of redline. The easiest way of determining your maximum downshift speed is to watch the tach and speedo as you are shifting up at redline. If you shift at redline from 2nd to 3rd at 60 mph, subtract 10 mph, and that becomes your effective maximum downshift point for 2nd gear. If are within 10 mph, you are better off staying in the higher gear.

HEEL-AND-TOE DOWNSHIFTS

This combines double-clutching and braking into one event. Place your foot on the brake as far to the right as you comfortably can. While braking, roll your ankle so you can catch the left edge of the gas pedal with the right edge of your foot. If the pedals are too wide, try placing the ball of your foot on the brake, and the heel on the gas (This is where the term heel-and-toe originally came from). Now try gently slowing down and downshifting. With practice, you can brake hard and downshift in one smooth motion. This will prevent the wheels from locking when the clutch is let out in the lower gear, and you will be ready for a burst of acceleration coming out of your favorite corner!

Copyright The Driver's Edge 1997

[JPL76]

Great info, but I'm afraid after a hard week, that put the old grey matter into hyperspace

[CharlieC]

Its about blipping the throttle between gears.

I always thought the heel was meant to be on the brake so maybe thats where I was goofing that one.

Never tried on the Esprit mind but will probably start practising on the civic first!

[Quicker]

about 17 - 20 secs in is the first good shot

[t70]

That's exactly how i do it... right side of the foot on the gas and left side of the foot on the brake. I've never used the heel on the gas and the toe on the brake... it's too much of a foot contortion. Much easier to regulate the pressure on the brake with using the "twist of the foot" method.

[Autocross7]

Yep, that's me - twist the foot. it is easy on the Esprit as the pedals are so close. the read above is good as i actually had to think about how I do. I have just been double clutching for so long it is hard for me to say how I do it?!

I also left foot brake if I need to slow down just a little - not enough to down shift.

Cameron

[Dan]

A question for those who can heel-and-toe in the Esprit: how tall are you?

I'm just over 6 foot, and can't get my ankle to a comfortable (confidence inspiring?) position due to my knee hitting the wheel. I've tried rolling, but my foot seems too low for the throttle already, and twisting, but this just shoves my knee against the wheel more. My knee is held off to the right of the wheel so my foot is coming onto the brake pedal at an angle already (right side lower). Seems very contorted to then lift or twist the right (lower) side of my foot onto the throttle. I notice in the videos the wheels seem to be mounted well clear of the knees, so movement is free for the driver.

I'm driving in, er, ballet shoes for want of a better term, and am happy with the principle as I double-declutch on most downshifts in most vehicles. I even double-declutch in my daily drive Land Rovers, which impresses the sheep I suppose

Any tips or comments?

Edited February 8, 2008 by Dan

[Vulcan Grey]

I'm 6'2" with 6'5" legs and size 12shoes (US)

I heel and toe down shift while braking pretty much every time. My knee does pretty much hit my 89SE steering wheel (the Nardi), so I can't rotate my leg much, I have to "heel-toe" with the left side of the ball of my foot on the brake, and rolling my ankle to hit the gas.

Like this

Not like this

I do this in my Acura 6speed as well.

I wear fairly wide shoes that are almost exactly as wide as the distance from my carpet to the edge of the brake pedal (tiny bit less than that gap).

My pedals are perfect in that as the brake pedal comes slightly down (pretty rock hard, the Esprit brake pedal) it is just the right distance from the gas pedal.

Edited February 9, 2008 by Vulcan Grey

[Jonathan]

I do that no matter the car - changing down I always offer a little throttle. The Esprit is a great car to heel and toe, the pedal box being so close together all you have to do is roll your foot slightly, could never do it in the Elise though which was really annoying.

[t70]

Though.. the most fun is in a Lori... left foot on the brake pedal and right foot on the throttle... 18 gears up... 18 gears down... apply brake hard... initiate drift... accellerate...

[Clark]

First time I was aware of double clutching was after watching 'Bullitt' and hearing Steve McQueen double clutch (shifting up) in his Mustang, I just loved the noise.

A couple months into owning my Esprit, and after talking with a few Lotus owners, I got in the habit of always double clutching when shifting down, and was pretty easy to get the hang of.

Heel-toe I'm still working on and would like to get good at. Maybe 1 out of every 3 attempts turn out well, the rest of the time I give it too much gas or not enough. For fear of embarassing myself in public, I usually do braking and double clutching seperately when in traffic and save heel-toe practice for side streets.

[Lowtus]

What's all this then? Double de-clutching went out with the ark. Sounds like a relation of the "I can brake better without antilock" nonsense.

With any synchromesh gearbox (which covers just about everything made in the last 50 years) double-clutching is neither necessary nor desirable. What's the point of pushing the pedal twice when you only need to push it once? Unless you like slow gear changes. As someone has rightly pointed out already in this thread it's mechanical sympathy in matching the rev's which counts and there's no need for outdated dancing on the pedals!

If you really want to play the "driver skill" game then change gear without using the clutch at all and without grinding gears. Can be very satisfying if you get it right but don't do it too often. That really will lead to accelerated synchro wear.

[t70]

Actually... double clutching reduces wear on the synchromesh and on the clutch. Though it is not necessary... it's still better on the gearbox and clutch. If you do it right... you blip the throttle as soon as the clutch is depressed the first time while maximum braking and very quickly double-clutch... and you'll not have to hit the throttle again. When down shifting this method is actually faster because of the inability of the synchros to catch up fast enough without the assistance of the throttle and double clutching. As for stopping quicker without abs.... very few abs systems on dry pavement can threshold brake as good as a good driver. I have tried with GM's to get the same stopping distance with the abs... it can't be done. There is a pedal position difference of about 1/2 inch -- ie less braking pressure = longer stopping distance. You can actually feel the braking force letting up as the abs kicks in... but I will admit that most of todays ABS systems are superrior to older generations and with my VW... I can't brake any better than the ABS. Using VW as an example... brings me to the DSG transmission -- which does double clutch by itself... there are two 3-speed transmissions and 2 seperate clutches. As the transmission gears down from 3rd to 2nd the following happens -- the first transmission's (the one with 1st, 3rd and 5th and reverse) clutch disengages and the engine computer revs the engine up to match the necessary rpm for 2nd gear and the second transmission's (the one with 2nd, 4th and 6th) clutch engages. As for how good this is for the transmission... we've NEVER replaced a DSG transmission clutch at the dealership.

[USAndretti42]

I think Otis made a good point. Double declutching can reduce gearbox wear if you do it right. If you do it right every time that is. Most people don't.

I used to be a regular double-declutcher until I went to the Jim Russel racing school at Mallory Park many moons ago. The Formula Fords they used didn't have synchromesh in the gearboxes as it makes it too time-consuming to change gear ratios when setting up the car. But they didn't teach students to double-declutch. Instead they used a technique they called "gassing in gear." Basically its double declutching without the double declutch bit. You blip the throttle as you dip the clutch and pull out of gear to match the revs for the next gear. Works fine on non-synchro boxes and doesn't damage the synchro on normal boxes if you mistime it.

With a sequential shift on a modern race car no-one double declutches. Some driver use the "gassing in gear" technique while others don't use the clutch at all.

[t70]

I do believe that most of todays racing tranny's use a dog-clutch system.. and the tranny's aren't meant to last. The DSG transmission has been around since the 70's but couldn't be used in normal vehicles due to excessive clutch wear (the rev's werent match between shifts).

[Advantage]

I used to have to double de clutch on my old 1960's Series 11a Land Rover. It didn't have synchros in the lower gears, so unless you were fairly brutal with the gearlever and immune to crunching noises, it wouldn't change gear any other way.

I don't bother on a modern car. There's no real point. By the time you've done all that you've reached the corner but still halfway through the gearchange.

All this talk about saving wear? It's what the synchros were designed for. If you want to stop the 'box from wearing out, you can always switch the car off and push it into the garage and use a bicycle- that way you'll save wear on just about everything.

[tonyp]

Must admit I thought double de-clutching only worked for old massive gearboxs, where the huge mass of the various shafts ensured they kept spinning for a bit. A bit of throttle blipping (& thats technically not really double d-c) to match revs always makes smooth downshifts, at least when you get it right. Heel & toeing very satisfying when you get it right - not easy on the Esprit as the pedals are not ideally placed. Or at least not for my clodhopping feet. Porsche Boxster near perfect.

Never did understand why Steve McQueen double blips on upchange (3rd - 4th) - those Muncie boxes are not so slow & heavy to shift are they ? Does sound absolutely great though, one of the all time great motoring clips.

Great thread BTW - late braking - thats a serious weakness for me (always brake too soon - talking track time here mind ...)

[andydclements]

I'm with Tony in not seeing any benefit to double de-clutching on an upshif, unless it's somebody who measures their gear change times by calendars.

The whole point is to match the rotational speeds of the teeth of the box, and when upshifing you need the input shaft to slow down slightly to achieve this.

In many of my previous cars I've been guilty of not using the clutch enough, or at all during some upshifts, remove the foot from the throttle for a split second, whatck it into the next gear and foot back on (OK, foot back flat to the floor).

Downshifting is a different matter, and where the car doesn't have a ynchro hub for 1st gear you have 2 choices, which don't really damage teeth of cogs, either stop the car and engage 1st or double de-clutch, but more cars now have synchro 1st than used to (as mentioned many didn't used to have them below 3rd before that). Even without doubel declutching you can reduce clutch wear, by accelerating to get the flywheel and clutch friction pate speeds matched before bringing the drive back into place, so I tend to do that (as a clutch in these cars isn't cheap or easy to do).

Andy

[tonyp]

Ha ha - the sort of cars I've had that had no synchro on 1st - you'd be stationary anyway when you needed to get to that gear (think A35, A40, old Landy stuff etc. You know, going up Hardnott pass in 2nd, revs dropping woefully, at the last gasp you swap into 1st, engine roaring lustily (ahem) doing all of - err 3 mph.

[andydclements]

I know that sort of 1st gear.

far worse though.

One of my current cars has a 0-60 time measured with a coin.

Heads it will get to 60........

1968

998cc

Auto 3 speed

Andy