I've heard and read a bit about this shifting technique and how it helps relieve stress/wear on the synchros in a manual transmission. What can you guys tell me about the mechanics of it and its benefits?
Double clutch shifting, what does it entail?
- Thread starter HyundaiAbuser
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When up shifting go to neutral, let out clutch with no gas, clutch in and shift into higher gear. This slows the syncro's down for the higher gear change.
When down shifting, go to neutral, let out clutch, give it a blip of throttle, clutch as you go into lower gear.
The whole point is to either slow down or speed up the snycro's as you either up shift or down shift matching the syncro speed to the gears you want.
When down shifting, go to neutral, let out clutch, give it a blip of throttle, clutch as you go into lower gear.
The whole point is to either slow down or speed up the snycro's as you either up shift or down shift matching the syncro speed to the gears you want.
Double clutching was common on old cars and trucks but I have not had to do it since I got rid of a Chevy 20 3/4 ton pickup with a straight six and 3 on the tree. It would grind trying to get it into gear sometimes or if you ran one gear out to far before shifting. The syncros were never great but as it aged it got worse and you had to double clutch it if you wanted to get it into gear. I have not had a manual transmission since the early 90's that had that kind of problem. Of course old manuals used to go through clutch plates and springs every 15k-20k miles (might have had something to do with the way we drove in high school). Now clutches seem to be life of the car/truck and syncros are light years ahead of what they were.
You would typically double-clutch in downshifting, not so much in upshifting. I assume that you shift smoothly and reasonably slowly when upshifting... i.e. out of the lower gear, then pause a short while in neutral, and then into the next gear. That is easy on the synchromesh parts. AND, you do not grab the shifter with your whole hand-grip... you only motivate the stick with two fingers, in the direction you want it to go in... Let the synchro do its job, and do its job AT IT's PACE.
For double-clutch downshifting typically you kick-in the clutch and take it out of gear, placing it in neutral. Depending on the clutch and/or transmission you may have to only kick-in the clutch half-way (to take the stick out of gear... and to place it into neutral) before you let the clutch out again. So... 1/2 kick of the clutch and place stick into neutral and then release clutch pedal fast.
Now with the clutch pedal NOT pushed, you rev up the car to more or less exactly match the revs you would do when in the lower gear, if it were in that lower gear with clutch out... It is not so much a jab of the accelerator... Rather, you push and hold the accelerator to the right point as described. That takes a bit of practice and judgement on your part. In any case, with the accelerator continually held at the correct (higher) rpm, you decisively push in the clutch fully and really shortly after (or during the clutch-pedal-stroke down) you get into your lower gear on the stick. You are STILL holding the acc. at the correct rpm. Then you let out the clutch, fairly quickly (and indeed, if your rpm is correct, you let it out really quickly)... and there is neither any acceleration of the vehicle, nor any compression-braking of the vehicle... because your rpm is perfect for the roadspeed. You can see that this means very little wear on the synchronizer for that lower gear, and it also means very little wear, actually zero, for the clutch disk, too.
Once you have perfected your double-clutching (A.K.A.double-declutching in much of the world except the USA or Canada) you can see if you want to do "heeling and toe'ing" combined with double-clutching. That is the 'real fun ballet-dancing move on the pedals...
For double-clutch downshifting typically you kick-in the clutch and take it out of gear, placing it in neutral. Depending on the clutch and/or transmission you may have to only kick-in the clutch half-way (to take the stick out of gear... and to place it into neutral) before you let the clutch out again. So... 1/2 kick of the clutch and place stick into neutral and then release clutch pedal fast.
Now with the clutch pedal NOT pushed, you rev up the car to more or less exactly match the revs you would do when in the lower gear, if it were in that lower gear with clutch out... It is not so much a jab of the accelerator... Rather, you push and hold the accelerator to the right point as described. That takes a bit of practice and judgement on your part. In any case, with the accelerator continually held at the correct (higher) rpm, you decisively push in the clutch fully and really shortly after (or during the clutch-pedal-stroke down) you get into your lower gear on the stick. You are STILL holding the acc. at the correct rpm. Then you let out the clutch, fairly quickly (and indeed, if your rpm is correct, you let it out really quickly)... and there is neither any acceleration of the vehicle, nor any compression-braking of the vehicle... because your rpm is perfect for the roadspeed. You can see that this means very little wear on the synchronizer for that lower gear, and it also means very little wear, actually zero, for the clutch disk, too.
Once you have perfected your double-clutching (A.K.A.double-declutching in much of the world except the USA or Canada) you can see if you want to do "heeling and toe'ing" combined with double-clutching. That is the 'real fun ballet-dancing move on the pedals...
Heel & Toe is the faster, smoother, more up-to-date technique to allow smooth downshifts in a syncro-box equipped car.
https://en.wikipedia.org/wiki/Heel-and-toe_shifting
https://en.wikipedia.org/wiki/Heel-and-toe_shifting
Originally Posted by Olas
Heel & Toe is the faster, smoother, more up-to-date technique to allow smooth downshifts in a syncro-box equipped car.
https://en.wikipedia.org/wiki/Heel-and-toe_shifting
Por que no los dos? :]
I do rev-matched double-clutched downshifts when I'm not driving enthusiastically.
Heel & Toe is the faster, smoother, more up-to-date technique to allow smooth downshifts in a syncro-box equipped car.
https://en.wikipedia.org/wiki/Heel-and-toe_shifting
Por que no los dos? :]
I do rev-matched double-clutched downshifts when I'm not driving enthusiastically.
Originally Posted by d00df00d
Originally Posted by Olas
Heel & Toe is the faster, smoother, more up-to-date technique to allow smooth downshifts in a syncro-box equipped car.
https://en.wikipedia.org/wiki/Heel-and-toe_shifting
Por que no los dos? :]
I do rev-matched double-clutched downshifts when I'm not driving enthusiastically.
I dont speak Spanish I'm afraid.
Point is, double declutching is useless in a syncro box, you can get the same smooth change in less time with HnT.
Originally Posted by Olas
Heel & Toe is the faster, smoother, more up-to-date technique to allow smooth downshifts in a syncro-box equipped car.
https://en.wikipedia.org/wiki/Heel-and-toe_shifting
Por que no los dos? :]
I do rev-matched double-clutched downshifts when I'm not driving enthusiastically.
I dont speak Spanish I'm afraid.
Point is, double declutching is useless in a syncro box, you can get the same smooth change in less time with HnT.
Is floating the gears easier on the trans than double clutching? I know its easier on the clutch as its not used.
I would think double clutching would double the wear on the clutch mechanisms.
I would think double clutching would double the wear on the clutch mechanisms.
Originally Posted by krismoriah72
Is floating the gears easier on the trans than double clutching? I know its easier on the clutch as its not used.
I would think double clutching would double the wear on the clutch mechanisms.
When you say 'floating the gears' do you mean clutchless gearchange? If you do, then;
If the engine speed is matched to the road speed then the gear will go in with no grinding and no wear. if the engine speed does NOT match the road speed then it will grind and suffer acclelerated wear. clutchless changing is a bit of an art form, once you know what RPMs you need for that roadspeed you only need to use the clutch to pull away from being stopped. just have to match the speeds.
Is floating the gears easier on the trans than double clutching? I know its easier on the clutch as its not used.
I would think double clutching would double the wear on the clutch mechanisms.
When you say 'floating the gears' do you mean clutchless gearchange? If you do, then;
If the engine speed is matched to the road speed then the gear will go in with no grinding and no wear. if the engine speed does NOT match the road speed then it will grind and suffer acclelerated wear. clutchless changing is a bit of an art form, once you know what RPMs you need for that roadspeed you only need to use the clutch to pull away from being stopped. just have to match the speeds.
Originally Posted by HyundaiAbuser
I've heard and read a bit about this shifting technique and how it helps relieve stress/wear on the synchros in a manual transmission.
It's more to prevent grinding the gears on a worn out transmission. If it's in good condition and not making noise, there is no need to. Shifting a manual should be a pleasure, doing this is a chore and you will eventually avoid driving it at all.
I've heard and read a bit about this shifting technique and how it helps relieve stress/wear on the synchros in a manual transmission.
It's more to prevent grinding the gears on a worn out transmission. If it's in good condition and not making noise, there is no need to. Shifting a manual should be a pleasure, doing this is a chore and you will eventually avoid driving it at all.
After owning a 1929 Model with no syncro's, you get used to it and the sound upshift without double clutch but downshifts require it since it took awhile for yhat huge flywheel to slow down.
Unless you own an old vintage car or a Peterbilt, double clutching is unnecessary in cars or trucks built in the last 50 years. I remember back in the day having to double clutch heavy trucks in order to change gears. No other choice, nature of the beast. Nowadays most class 8 trucks are automatics. However It is fun to do on a rural road in an old car on Sunday mornings.
Some new cars use the cars computer to REV match the engine and transmission during gear changes which is what double clutching does. Same thing when rolling up to stop. In any gear when the tachometer is at idle speed you can easily slip into neutral without pushing in the clutch. I do it all of the time in 4 of my vehicles when I know I will be sitting at a light with no one coming up behind me of course. The real trick to driving any manual transmission is learning how to shift it smoother than an automatic transmission can, and other than the sound no one in the car should even feel it. I can always tell if I don't make a seamless smooth move shifting or braking, because you see the passenger turn into a bobble head. Not many people know how to drive smoothly, and you should learn to fly it like an airplane.
All very interesting, the second gear synchros in my tiburon are starting to show a little wear and i was looking for the ways to take some of the workload off of them when i came across this. I'll do a bit more research on the heel toe method too.
Originally Posted by Olas
https://www.pistonheads.com/gassing/topic.asp?h=0&f=154&t=1507379
^
Very good explanation from Piston Heads. Not long winded at all.
https://www.pistonheads.com/gassing/topic.asp?h=0&f=154&t=1507379
^
Very good explanation from Piston Heads. Not long winded at all.
Originally Posted by Olas
When you say 'floating the gears' do you mean clutchless gearchange? If you do, then;
If the engine speed is matched to the road speed then the gear will go in with no grinding and no wear. if the engine speed does NOT match the road speed then it will grind and suffer acclelerated wear. clutchless changing is a bit of an art form, once you know what RPMs you need for that roadspeed you only need to use the clutch to pull away from being stopped. just have to match the speeds.
Originally Posted by Traction
If you match engine speed, and transmission speeds carefully, you can actually shift up, or down without even pushing in the clutch. I've driven a couple cars home with after the clutch linkage had fallen off.
I think it was Olas that said it above, you use your fingers on the gear selector, not grab it firmly and slam it between gears. I've had to drive a car with no clutch (well, the slave cylinder had failed) and have also shifted gears without the clutch just to show someone it's possible. Once rolling/accelerating, gently move the selector from a gear to neutral, then lightly feather it into the 'gate' for the gear you want. Do it so lightly that you can feel when it will slip in nicely. No racing-style, heel-and-toe or throttle blipping is really needed with practice.
When you say 'floating the gears' do you mean clutchless gearchange? If you do, then;
If the engine speed is matched to the road speed then the gear will go in with no grinding and no wear. if the engine speed does NOT match the road speed then it will grind and suffer acclelerated wear. clutchless changing is a bit of an art form, once you know what RPMs you need for that roadspeed you only need to use the clutch to pull away from being stopped. just have to match the speeds.
Originally Posted by Traction
If you match engine speed, and transmission speeds carefully, you can actually shift up, or down without even pushing in the clutch. I've driven a couple cars home with after the clutch linkage had fallen off.
I think it was Olas that said it above, you use your fingers on the gear selector, not grab it firmly and slam it between gears. I've had to drive a car with no clutch (well, the slave cylinder had failed) and have also shifted gears without the clutch just to show someone it's possible. Once rolling/accelerating, gently move the selector from a gear to neutral, then lightly feather it into the 'gate' for the gear you want. Do it so lightly that you can feel when it will slip in nicely. No racing-style, heel-and-toe or throttle blipping is really needed with practice.
Originally Posted by Traction
Some new cars use the cars computer to REV match the engine and transmission during gear changes which is what double clutching does.
Same thing double-clutching does in terms of rev (matching); not the same (beneficial) thing that double-clutching does in terms of saving synchro wear. Reving while in neutral is the only thing that does that. And I note that dual-clutch automated manuals do NOT rev match while in neutral. So for folks who love the sound and feel of the car while rev-matching at high road-speeds, whether you have a conventional manual transmission or a DCT/PDK/or VW variant (name escapes me) - if you wantonly downshift - you WILL knacker your synchro's prematurely. The amount of force at the gearstick, required to downshift, versus on an easy upshift by comparison, tells the tale of synchro duress and wear...
It's not so much WILL it go into gear, but rather, how much you have to FORCE it to go into gear. Double-clutch accurately and the force is next to ZIPPO.
Some new cars use the cars computer to REV match the engine and transmission during gear changes which is what double clutching does.
Same thing double-clutching does in terms of rev (matching); not the same (beneficial) thing that double-clutching does in terms of saving synchro wear. Reving while in neutral is the only thing that does that. And I note that dual-clutch automated manuals do NOT rev match while in neutral. So for folks who love the sound and feel of the car while rev-matching at high road-speeds, whether you have a conventional manual transmission or a DCT/PDK/or VW variant (name escapes me) - if you wantonly downshift - you WILL knacker your synchro's prematurely. The amount of force at the gearstick, required to downshift, versus on an easy upshift by comparison, tells the tale of synchro duress and wear...
It's not so much WILL it go into gear, but rather, how much you have to FORCE it to go into gear. Double-clutch accurately and the force is next to ZIPPO.
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