Do you double-declutch, or just heel-toe on the race track?

[Doug Gould]

I heard that painting flames down the side picks up more time than double clutching.

Doug Gould

[Sheldon McIntosh]

I heard that painting flames down the side picks up more time than double clutching.

Most definitely, probably picks up more DDs as well. 

[scott.venables]

regarding the speed of the input shaft, Is this why transaxle synchros always go so quickly, because it's got all the momentum of the driveshaft to speed up/slow down?  I've asked a couple of people with Porsche 944s (they're also rear transaxle aren't they?) and they've never had probs with synchros.

This is why I think a rear clutch is better.  When the clutch is disengaged for changing gears, the synchros only have to speed/slow down the clutch, but with a front mounted clutch(like the 924/944 etc I think) the synchros have to speed up/slow down the entire driveshaft and the clutch.  Still doesn't explain why the Alfa synchros wear out

[Evan Bottcher]

I thought that transaxle cars had a much smaller flywheel, as the driveshaft itself adds to the flywheel effect - is this true?

[a sharp]

Yes, the syncros wear very quickly in a 116 or 105 and it's not long after a change and the grinding is back, and then the only way is to double or replace.

I think the bottom line is if you are in a syncromesh car with good syncros doubling is really redundant and could cost you time.  Rely on the sycros to match gear speed, a big rev on the down change to match road speed and slam it thru....

Scott do you own shares in the Syncro company, If you only DD when the box starts to grind you have already started the process that leads to rebuilding the box. I have DD since I first started driving on every change down, except on the few cars I could do clutchless changes. (PS do not do cluchless changes in 116's, if you don't get it perfect you end up with a broken box, just ask Alan Jones he destroyed heaps of boxes in the ingus car, Bondy never broke 1).

If you want long life from your Syncro's then DD, my 116 GTV has done over 440,000kms and has never had a synco put in it, I also have never had to replace the diff, a common failure on Transaxles. It would be fare to say that the car was driven with mechanical simpathy all its life, but was always driven hard with a 180hp motor, it was use for sprints, hammered over 10's of thousands of km of mountain passes, including gravel and even used for recey and setups no rallys, dirt not tarmac.

Anthony

[Scott Farquharson]

Yes, the syncros wear very quickly in a 116 or 105 and it's not long after a change and the grinding is back, and then the only way is to double or replace.

I think the bottom line is if you are in a syncromesh car with good syncros doubling is really redundant and could cost you time.  Rely on the sycros to match gear speed, a big rev on the down change to match road speed and slam it thru....

Scott do you own shares in the Syncro company, If you only DD when the box starts to grind you have already started the process that leads to rebuilding the box. I have DD since I first started driving on every change down, except on the few cars I could do clutchless changes. (PS do not do cluchless changes in 116's, if you don't get it perfect you end up with a broken box, just ask Alan Jones he destroyed heaps of boxes in the ingus car, Bondy never broke 1).

If you want long life from your Syncro's then DD, my 116 GTV has done over 440,000kms and has never had a synco put in it, I also have never had to replace the diff, a common failure on Transaxles. It would be fare to say that the car was driven with mechanical simpathy all its life, but was always driven hard with a 180hp motor, it was use for sprints, hammered over 10's of thousands of km of mountain passes, including gravel and even used for recey and setups no rallys, dirt not tarmac.

Anthony

I should clarify, I, out of habit, have always DD, in all cars I am driving...and I have always DD in the Dulux, however from competition point of view in a number of situations/cnrs, it is faster to simply sacrfice the syncros in a 105/116 gearbox for the speed and just heel/toe and not DD, and as Jim said just change them regularly.  If you have a gearbox with good syncros (ie. not an alfa) you can do this and it may be quite a long time before you need a change.  I'll think you'll find in say the WRX club that not many would DD because it's simply not an issue in a WRX.

If you simply want to save syncros then by all means DD all the time.

My point above was that once you have grinding then the only way not to grind is to DD.  Not that the way to save a gearbox once there was grinding was then to DD.

I think it depends on your objective - if you want to just make syncros last then sure DD all the time, but as i said on some cnrs there is a penalty for DD and a simple heel/tow and let the syncros do the work is the fastest.

[Paul Newby]

I'm a bit late to discussion, but I will add my two cents worth ...

I always understood that double-declutching was when you didn't use the brake ie changing up gears in a non-synchro box (or a truck) or using the gears to slow you down when downchanging.

I always understood hee-toe as incorporating the brake pedal into your double-declutch.

In the first instance I double-declutch, or use the gears to help slow me down when I'm driving my road car. Often you find yourself in a situation in the road where you've slowed down in traffic (coasted) without using the brakes and need to select a lower gear, so I just blip the throttle, double-declutch and make a smooth gear change.

In a racing situation you never you the gears to slow down - that is what the brake pedal is for!  As a few have said before in this thread, you will always be on the brakes long enough for you to double-declutch on the downchange. Ok, I might double-declutch every gearchange - I will often go straight from 4th to 2nd for Honda Hairpin at Phillip Island, but I will always double-declutch - its smoother and easier on the machinery. And as club racers we have to look after the gearbox - no one can afford to get then rebuilt every second race meeting...

Honestly I would be very surprised that anyone in our form of racing would not double-declutch, whether we are using synchro or dog boxes.

have a look at the "foot-cams" they sometimes deploy in the V8 Supercar coverage. All those cars use 6 speed Hollinger dog-boxes. You will see that they flat change up the gears without using the clutch (though some drivers have taken to using the clutch for across the gate changes - 2nd to 3rd and 4th to 5th. When they change down gears all the drivers with one exception are using the clutch to select the gears and are thus double declutching on their heel-toe changes.

You may ask who that one exception is? well as far as I know Greg Murphy is the only V8 driver who left foot brakes, which means he isn't using the clutch at all and must deploy what we consider in this thread to be the true "heel-toe." I'm not quite sure how he does it (I believe it's a common practice where sequential boxes are used, eg old Lola Champ Cars from 2006 and before) but he must be good at it as I reckon it would be tough on the gearbox...

[jimnielsen]

[quote ........

I always understood that double-declutching was .......  or using the gears to slow you down when downchanging.

..Um no, this is using the engine braking capability of the car to produce a slowing effect. Taken too far the compression of the engine will cause the driven wheels to lock up - its not how you drive a racecar. Anyone can "flatshift" given the hardware and software required to make this work (like in a v8 supercar). On an standard alfetta gearbox however the heel toe or DD maneuvers discussed in this thread are actually required to have any chance of shifting from (say) 5th to 2nd at high revs smoothly.

JimN ~

[Paul Newby]

Jim, I think we are getting stuck on semantics, or if you prefer terminology.

As I said I never use the gearbox to slow myself down on the track, but I do use the gearbox to "help" me slow down on the road and limiting use of the brakes - usually I'll double declutch down from 4th to 3rd and only incorporate the brakes for a heel and toe change back to second as I'm coming up to an intersection.

Maybe that is why (on my 01 Honda Integra Type R with 110K) I'm onto my second clutch but still on my first set of front brake rotors... 

[Big Trev]

As a long time driver trainer (heavy vehicle mostly), you should never double de-clutch a synchromesh gearbox, you are getting the synchro's to work twice as hard as they were intended/desgined to.   Just for interest sake, Volvo trucks will void warranty if they can prove that a driver is double de-clutching one of the synchromesh truck gearboxes.

It has been an eacceptable practice, that when synchro's are getting a bit dodgy that you double de-clutch, but it isn't the correct thing to be doing, but it does aid the trasmission selecting a gear.

Why do synchro's wear out? Normally because people select a gear at a too high gear, e.g. using the gearbox as a brake.  Syncro's are designed to help match speed of gears, however if the variation of speed is too great then the synchro's wear out very fast.

The heel-toe is the prefered version (on a race track)

[Colin Byrne]

I'm struggling a bit with this concept

you should never double de-clutch a synchromesh gearbox, you are getting the synchro's to work twice as hard as they were intended/desgined to

The way I see it is if collar and gear are speed matched (double-declutching) then the only wear occurring on the synchro-rings is from the transverse movement of the collar, however if the speeds are not matched (normal shifting) then the synchro-rings get the same wear from the transverse movement plus the additional wear from the rotational movement.

Why do synchro's wear out? Normally because people select a gear at a too high gear, e.g. using the gearbox as a brake.  Syncro's are designed to help match speed of gears, however if the variation of speed is too great then the synchro's wear out very fast.

If this is the case, which I don't disagree with, then how does reducing this speed difference as much as possible (double-declutching) wear the synchro out twice as fast?

Any chance of a further explanation Big Trev?

[Big Trev]

I am no mechanic, but I have a good understanding of the workings, so I will try to explain what I mean.  If you push the clutch in and pull the gear lever out of gear then put the gear lever in a position of the next gear you want, then as soon as the gear of the selector starts pushing agains the synchro's then there is friction to slow down or speed up the gear you are trying to select - correct? 

When the sped difference is at its lowest or there is least resistance then the gear will be selected - correct?

If at the point when the gearbox is in neutral and you are pushing against the syhncro and then you de-clutch again you are taking the spin off (or power from) the input shaft which means the gearbox is free-wheeling and you then let the clutch out again the input shaft starts to spin a different speed and the syhncro is sitting there spinning aagainst the cone (or gear being selected), thus causing extra wear.  It is like having 2 bites at the cherry if you like.

Hope that is easier to understand.  All transmission manufacturers highly disapprove of double de-clutching a synchro box, do a google search and see what I mean.

[Colin Byrne]

If at the point when the gearbox is in neutral and you are pushing against the synchro and then you de-clutch

Sorry Trev I still don't follow, why are you pushing against the synchro at this point in the sequence,  During the time at which the gearbox input shaft is re-connected to the engine (clutch pedal up then clutch pedal down) the gearbox should be in neutral-> no pressure on the selector forks-> no pressure on any synchro rings.  It's only after the input shaft has been disconnected from the engine (clutch pedal down) after the speed matching has been completed that the synchro should begin to make contact

As long as the gearbox is in neutral during the speed matching process I still can't see how this creates extra wear.  If this was the case then wouldn't just revving your engine in neutral whilst stationary wear out our synchros as well?

[shane wescott]

Awesome explanation Mate. I feel like I understand a little bit of what happens in a gearbox now :-)

One question. Bearing in mind my own experience with alfa's goes back to my first car - a 1971 105 Berlina bought on L plates in 1979, why is it that Alfa's need to be double clutched when down shifting, especially from third to second.

Are the gear boxes just notoriously bad for synchros, or is it because the passion of us alfa drivers makes us drives the cars to the stage where the double clutch is required to extend the life of the synchros.

Interested in your opinion, I've always DC down the gears with all my alfas, just out of habit.

Catch ya

Shane

[Colin Byrne]

Anyway, I'm sure someone will want to argue,

No arguments here, great explanation (although it was a bit of a struggle trying to read it all on my mobile phone last night!)