Gear changes with clutch delay valve

[Somewhatfoolish]

Any recommendations on smooth gear changing on a car equipped with a clutch delay valve? Very easy to kangaroo from a start (interestingly this seems to be more likely if you're not accelerating briskly) and 1st - 2nd changes are not that easy either. Not so much of a problem going down gears as I tend to err on the side of blipping the engine a wee bit too much anyway.

Very seriously considering getting the CDV removed but before doing something that drastic would rather pick brains of people here for tips or perhaps a specific technique to try out. I've not really been able to find anything online (other than lots and lots of complaining about them).

[RWD cossie wil]

Hateful devices.....

[Somewhatfoolish]

I know

[Reg Local]

I've never found them a problem. Are you trying to change gear too quickly? If you're looking to smooth your gear changes out, one of my YouTube videos covers the finer points in detail:

https://www.youtube.com/watch?v=A4rs09AKBc8

[Ransoman]

Just remove it. I did and there are loads of videos and posts about the subject all over the internet.

[waremark]

What is a clutch delay valve, and what cars have them?

[RWD cossie wil]

waremark said:

What is a clutch delay valve, and what cars have them?

It's a restrictor in the hydraulic return line, so if you let your foot off the clutch pedal quickly, the valve delays the release.

For people who can actually drive they are horrific things, feels like the car is secondguessing you all the time.

Worst ones I have found are Mondeo/Focus diesels, but present in a lot of modern cars, along with horridly over servo' d brakes & a nasty e-throttle.

[Reg Local]

RWD cossie wil said:

For people who can actually drive they are horrific things

Thats me out then - no wonder I've never had a problem with them.

[Jonno02]

My cupra has it. Horrendous on a car that actively encourages fast gear changes.

[IcedKiwi]

waremark said:

What is a clutch delay valve, and what cars have them?

Lots of discussion about them on e46 and e90 M and non M BMWs (my brother removed his from his Z4MC). Can't say I've noticed it's effect in mine - I'm almost tempted to see if the first owner removed it such is magnitude of the problem that some people appear to have.

[Reg Local]

How exactly does a car "actively encourage fast gearchanges"?

[Reg Local]

IcedKiwi said:

Lots of discussion about them on e46 and e90 M and non M BMWs (my brother removed his from his Z4MC). Can't say I've noticed it's effect in mine - I'm almost tempted to see if the first owner removed it such is magnitude of the problem that some people appear to have.

I'm going to stick my neck out a bit and suggest that they're a device designed to minimise the damage caused by the clumpy of foot who jump off the clutch pedal.

Those of us who take the time to release the clutch pedal properly won't experience an issue with them.

[davepoth]

Reg Local said:

How exactly does a car "actively encourage fast gearchanges"?

Throttle mapping, flywheel weight, and gear ratios. If the revs drop to the speed for the next gear faster, you'll be able to make a synchronised upshift faster.

[Somewhatfoolish]

Reg Local said:

I've never found them a problem. Are you trying to change gear too quickly? If you're looking to smooth your gear changes out, one of my YouTube videos covers the finer points in detail:

https://www.youtube.com/watch?v=A4rs09AKBc8

I've read both your books, they're fantastic by the way

Been experimenting as advised and I think the key difference with what you're doing is what you refer to keeping the throttle on - as you say in the vid it's the "key to driving smoothly". Problem with a CDV is because the clutch is slipping whether you like it or not, you have to keep a bit more throttle on than you would to change gear smoothly without one. So to answer my question above, the answer is to put on more throttle than you would be doing with a normal clutch.

But this now means that you're slipping the clutch deliberately and also when you transition to another car you're going to be giving it a bit too many revs.

Not mechanically sympathetic

[Reg Local]

I'm struggling to understand why applying more throttle is the solution to your problem.

Is it possible that you're confusing "more" throttle with holding the matched revs for slightly longer?

The intention with rev-matching is to bring the revs up (for a downchange) or down (for an upchange) so that the engine speed is matched to the road, wheel and gearbox speed for the next gear. If engine speed and road speed are matched with accurate application of throttle, then both the friction face and flywheel face of the clutch will be rotating at exactly the same speed when the clutch is re-engaged. If the speeds are matched accurately, there will be no clutch slip whatsoever (in real terms, that would be minimal slip, rather than no slip).

So if the revs are matched, the speed of clutch release doesn't matter. Semi-automatic gearboxes can seamleslly rev-match gearchanges whilst changing gear extremely quickly.

With a manual box, however, if your aim is smoothness (and it should be), then you should take your time with the gearchange, match the revs (with a squeeze and hold of the accelerator, not a blip) and release the clutch pedal gently, rather than jumping off it or sidestepping it. If you release it a little more slowly, the release valve becomes irrelevant and you remain in full control of your gearchanges.

[Somewhatfoolish]

For simplicity imagine you're doing a down change, and you need to take the revs from 2000rpm to 4000rpm. As you're a perfect advanced driver you're doing this downchange to get into gear for a hazard and therefore aren't going to be adjusting speed at all.

So thinking in terms of what your accellerator pedal needs to be doing to keep balanced rpm between the sections of this change (made up figures):

Crusing along at 2000 rpm, fullly in gear - 25% down
Clutch depressed - remain at 2000 rpm initally for milliseconds - 25% down
Bring revs upto 4000rpm in an engine without load of drive train on it - ???% down
Sustain revs at 4000rpm in engine with load of drive train on it ?????% down.

The smooth n calm approach which I think you're advocating is basically to aim to give a bit more ??? than ?????. Works fine, but has the disadvantages I was getting at.

The crap approach is to give less ??? than ?????. Obviously st.

Now what I think most smooth quick gear changers do is they aim, even though they can't really explain why (as this post may be demonstrating), the exact same amount of throttle for ?? and ????. With perfect clutch timing, this will produce the smoothest possible change.

But because you're moving through the power band so quickly the timing really has to be perfect, and the CDV just ruins this, what you end up instead with is:

Bring revs upto 4500rpm in an engine without load of drive train on it - ???% down
React to revs going higher than expected during clutch release by moving throttle to ???%
Jerk as revs crash through 4000rpm as engine gets load of drive train with ??%
Again instinctive reaction to revs by opening throttle to ????%
Kangaroo time!

Notation I have used here means:

? = a throttle level
?? = a throttle level higher than, or equal to, ?
??? = a throttle level higher than, or equal to, ??, and also greater than 25%
???? = a throttle level higher than, or equal to, ???
????? = a throttle level higher than, or equal to, ????

Edited by Somewhatfoolish on Monday 30th January 23:13

[IcedKiwi]

Somewhatfoolish said:

Now what I think most smooth quick gear changers do is they aim, even though they can't really explain why (as this post may be demonstrating), the exact same amount of throttle for ?? and ????. With perfect clutch timing, this will produce the smoothest possible change.

Not 100% sure what you mean, but sounds like you apply more throttle than needed to maintain 4000rpm (in neutral), then try to catch it with the clutch just as it reaches (and wants to go past) 4000?

I try and go for the smooth relaxed approach rather than the smooth quick approach. For downchanges, I'll brake (if required) ease off the brakes, move foot to accelerator, then declutch, rev match, gear change, release clutch fully and only then apply drive. Making sure your foot is over the accelerator before declutching may feel slower but in reality should be quicker as there's no drop in revs to then increase again during the matching process - matching the revs should be easier too.

For the upchanges (including 1st to 2nd) I have a noticeable plateau in speed. Ease off the accelerator at desired rpm and aim to maintain it for a fraction of a second, then revmatched gearchange (requires some throttle application), wait until your clutch is fully engaged (still aiming to maintain the same constant speed that you eased off to), before applying throttle and off you go.

[waremark]

I think my style means I am not aware of these devices. How would I know which cars I have driven have them?

[james_gt3rs]

waremark said:

I think my style means I am not aware of these devices. How would I know which cars I have driven have them?

Do a non rev matched downshift by banging off the clutch. In a proper car you'd get a violent shunt, with the CDV it would change more smoothly. In practice I think it just requires a slightly different timing of the clutch to get a good change.

I used to alternate between cars with and without for a bit, and getting used to one always messed up my gearchange in the other until I adapted again.

[_Neal_]

IcedKiwi said:

Somewhatfoolish said:

Now what I think most smooth quick gear changers do is they aim, even though they can't really explain why (as this post may be demonstrating), the exact same amount of throttle for ?? and ????. With perfect clutch timing, this will produce the smoothest possible change.

Not 100% sure what you mean, but sounds like you apply more throttle than needed to maintain 4000rpm (in neutral), then try to catch it with the clutch just as it reaches (and wants to go past) 4000?

I try and go for the smooth relaxed approach rather than the smooth quick approach. For downchanges, I'll brake (if required) ease off the brakes, move foot to accelerator, then declutch, rev match, gear change, release clutch fully and only then apply drive. Making sure your foot is over the accelerator before declutching may feel slower but in reality should be quicker as there's no drop in revs to then increase again during the matching process - matching the revs should be easier too.

For the upchanges (including 1st to 2nd) I have a noticeable plateau in speed. Ease off the accelerator at desired rpm and aim to maintain it for a fraction of a second, then revmatched gearchange (requires some throttle application), wait until your clutch is fully engaged (still aiming to maintain the same constant speed that you eased off to), before applying throttle and off you go.

I agree with the above, and generally go for "smooth relaxed" too, with a plateau on upshifts, for daily driving. I had a E36 M3 Evo with a cdv and never noticed it to be honest, driven hard or gently.