Double Clutch & Double De-Clutch
Discussion
Somebody will explain better I'm sure but double de-clutching is used in cars with no syncromesh to engage the gears smoothly without grinding.
As you go to change up its something like this order:-
1.Off throttle
2.dip clutch put car into neutral
3.off clutch and blip throttle
4.dip clutch and engage in new gear.
All in the blink of an eye as well!
I think it spins the cogs up to a similar speed as those driven and therefore engages easier, I sometimes have to do it going from 2nd to 1st when cold, as the syncro is a bit knackered, and it helps engage much easier.
Anyway I think thats right(ish)!
As you go to change up its something like this order:-
1.Off throttle
2.dip clutch put car into neutral
3.off clutch and blip throttle
4.dip clutch and engage in new gear.
All in the blink of an eye as well!
I think it spins the cogs up to a similar speed as those driven and therefore engages easier, I sometimes have to do it going from 2nd to 1st when cold, as the syncro is a bit knackered, and it helps engage much easier.
Anyway I think thats right(ish)!
Thats right Nic,
As you let the clutch up in neutral and rev, the input shaft (connected to engine) speeds up the whole gearbox. The trick is to get this speed to match what the revs would be if you were in the gear you are changing to with the clutch up.
Eg, 4th at 50 say 4000 revs
3rd at 50 say 5000 revs
So as you come out of 4th and are passing through neutral, clutch up and rev to say 5500, clutch down and move into 3rd, clutch up.
Hopefully, as the clucth comes up in 3rd, the revs will be at 5000rpm, which in this example is what you want.
You are doing two things here.
1. Normally, moving into 3rd would cause the 3rd gear syncro to speed up the shaft so you can acutally "get it into gear". The double -de-clutch does this instead, so there is less wear on the syncro rings.
2. As the revs all match for the gear you're aiming for, there is no clutch slip as the clutch comes up, so less wear on the clutch.
In "modern boxes" the gear pairs are always in "mesh" (hence, constant mesh boxes). This would jam a gearbox and make it useless, so in fact one gear in each pair freely rotates on the shaft, and only the selected pair (say 4th) are locked onto the splined shaft by a selector. Say at this point the shaft is rotating at 3000 rpm, the 3rd gear would be rotating faster than the shaft (remember, it's not locked on at this point). As you move into 3rd, the selector pushes the syncro cone against the side of the, faster spinning 3rd gear, and friction causes the shaft to spin up to the speed of the third gear (say 3500rpm).
Hope this helps,
Martin
As you let the clutch up in neutral and rev, the input shaft (connected to engine) speeds up the whole gearbox. The trick is to get this speed to match what the revs would be if you were in the gear you are changing to with the clutch up.
Eg, 4th at 50 say 4000 revs
3rd at 50 say 5000 revs
So as you come out of 4th and are passing through neutral, clutch up and rev to say 5500, clutch down and move into 3rd, clutch up.
Hopefully, as the clucth comes up in 3rd, the revs will be at 5000rpm, which in this example is what you want.
You are doing two things here.
1. Normally, moving into 3rd would cause the 3rd gear syncro to speed up the shaft so you can acutally "get it into gear". The double -de-clutch does this instead, so there is less wear on the syncro rings.
2. As the revs all match for the gear you're aiming for, there is no clutch slip as the clutch comes up, so less wear on the clutch.
In "modern boxes" the gear pairs are always in "mesh" (hence, constant mesh boxes). This would jam a gearbox and make it useless, so in fact one gear in each pair freely rotates on the shaft, and only the selected pair (say 4th) are locked onto the splined shaft by a selector. Say at this point the shaft is rotating at 3000 rpm, the 3rd gear would be rotating faster than the shaft (remember, it's not locked on at this point). As you move into 3rd, the selector pushes the syncro cone against the side of the, faster spinning 3rd gear, and friction causes the shaft to spin up to the speed of the third gear (say 3500rpm).
Hope this helps,
Martin
When changing up, I always try and blip the throttle, to match the road speed to engine speed. But I don't double de-clutch. So the action is it's in 4th, clutch down, gear travel to third giving a controlled blip to raise the revs, clutch up.
I'm not sure if everyone is saying this shouldn't be done, or if you are referring to the actual 'double de-clutch' bit, i.e. the lifting of the clutch in the middle.
I always blip! Should I continue?
Regards
Sally
I'm not sure if everyone is saying this shouldn't be done, or if you are referring to the actual 'double de-clutch' bit, i.e. the lifting of the clutch in the middle.
I always blip! Should I continue?
Regards
Sally
A reflection on blipping which caught me out this weekend -- different cars require different inputs to "blip".
My daily driver is quite easy to give a little blip to and I found I wasn't getting smooth downchanges on the monster I was driving at the weekend, as the muscle memory in my right foot hadn't caught up with the fact that I had swapped cars.
Furthermore my tiny brain couldn't figure out that's what was going on.
My daily driver is quite easy to give a little blip to and I found I wasn't getting smooth downchanges on the monster I was driving at the weekend, as the muscle memory in my right foot hadn't caught up with the fact that I had swapped cars.
Furthermore my tiny brain couldn't figure out that's what was going on.
falcemob said:
Don't double de-clutch on a synchro box
Whyever not? Done properly it is an aid to synchronisation - you can use the engine and clutch rather than the cone clutches forming the synchromesh to do it and it can both speed up and reduce the pressure required on the gear lever to perform the change.
It's certainly handy if you're skipping gears on the way down the 'box. I had a chance to do a lovely 4-1 change yesterday and it wouldn't have worked if I'd tried jamming the lever across the gate. Worse than that is was a heel-and-toe change too!
But fond reminiscence aside, one of the advantages of running data logging in the car is that I can really examine what I actually do behind the wheel of the car. I was quite surprised (as I believed I was a confirmed 'blipper' of the throttle) to discover that I tend to use sustained revs rather than blipping. It's what I tend to teach to newcomers to the subject as it removes any time pressure for the change. Instead of blipping the throttle (which can be fraught with issues as every engine has different levels of inertia in the flywheel so requires different amounts of displacement and pressure on the throttle pedal to achieve) you raise the revs to the required level for the next gear and then complete the change. It's a different muscle memory that you need to learn but it's much more transferrable across cars.
StressedDave said:
falcemob said:
Don't double de-clutch on a synchro box
Whyever not? Done properly it is an aid to synchronisation - you can use the engine and clutch rather than the cone clutches forming the synchromesh to do it and it can both speed up and reduce the pressure required on the gear lever to perform the change.
I suppose if double de-clutching were to be done very clumsily, and the applied revs were seriously wrong, you could give the synchro mechanism extra work to do and thus do more harm than good. In general though I would think that those who take the trouble to acquire reasonable skill with the technique will derive useful benefits.
Best wishes all,
Dave.
Years ago whilst covering the nightshift on a dockyard I would amuse myself by learning to change down through a range change and a split whilst heel and toeing in an old Iveco artic, found some oily bits and tried cadence braking as well but that was a step too far! It passed the time but has never been that much use on the road though..............
StressedDave said:
falcemob said:
Don't double de-clutch on a synchro box
Whyever not? Done properly it is an aid to synchronisation - you can use the engine and clutch rather than the cone clutches forming the synchromesh to do it and it can both speed up and reduce the pressure required on the gear lever to perform the change.
I suppose I should have said, you shouldn't double de-clutch on a synchro box mainly for the reason you say in the first sentance..."Done properly". Not many people know how to as a few on here have proved with their comments.
StressedDave said:
I was quite surprised (as I believed I was a confirmed 'blipper' of the throttle) to discover that I tend to use sustained revs rather than blipping. It's what I tend to teach to newcomers to the subject as it removes any time pressure for the change. Instead of blipping the throttle (which can be fraught with issues as every engine has different levels of inertia in the flywheel so requires different amounts of displacement and pressure on the throttle pedal to achieve) you raise the revs to the required level for the next gear and then complete the change. It's a different muscle memory that you need to learn but it's much more transferrable across cars.
Agreed. Much more consistent I find (or used to find, since most of my driving these days is in an auto). Not quite as quick on the change, perhaps, as can be achieved through blipping but a much better hit rate across different vehicles and far easier and more accurate when heel and toeing or trail braking whilst going down the box on a bend - or any of those other things that the system says you should avoid.
Then there is not using the clutch at all ... at least once moving. An especially informative thing to practice for 1st to 2nd and 2nd to 1st changes.
vonhosen said:
Danke
If you double de clutch properly, you do not need to use the clutch at all.
You can successfully change gear either up or down the box by synchronising engine revs to road speed to selected gear speed.
You only need the clutch depressed when you start from 0 mph to select 1st gear. Either that or put the car in 1st gear with the engine off and then start it wilst in first gear. From that point on if you are practiced enough, no need for clutch at all, even when coming to a stop!
You can successfully change gear either up or down the box by synchronising engine revs to road speed to selected gear speed.
You only need the clutch depressed when you start from 0 mph to select 1st gear. Either that or put the car in 1st gear with the engine off and then start it wilst in first gear. From that point on if you are practiced enough, no need for clutch at all, even when coming to a stop!
Gassing Station | Advanced Driving | Top of Page | What's New | My Stuff