Have any of you done the CDV delete?

[zj96sc]

The CDV was originally there to prevent people who are inexperienced or just bad at driving a stick from destroying a clutch in 40k miles. It lessens the wear on the clutch if you dump it or- for a new driver- rev too high and burn the clutch.

I was asking it as a theoretical question to wsmeyer.

I think you've actually got that backwards - in both of those cases the CDV would actually increase wear due to longer clamp up time therefore longer slip time, heat, etc. The CDV intent I believe is largely NVH - just another "buffer" to soften up the drivetrain feedback to the cabin.

[zhp43867]

I was asking it as a theoretical question to wsmeyer.

I think you've actually got that backwards - in both of those cases the CDV would actually increase wear due to longer clamp up time therefore longer slip time, heat, etc. The CDV intent I believe is largely NVH - just another "buffer" to soften up the drivetrain feedback to the cabin.

I just worded it wrong, here's what zeckhausen says:

Theory of Operation - What is a CDV?

The Clutch Delay Valve (CDV) is a one-way restrictor installed by the factory between the clutch slave cylinder and clutch master cylinder, as shown in Figure 1. It "delays" the engagement of the clutch, much like old record players use a damped tone-arm to gently lower the needle onto the surface of a record.

Because of this valve, no matter how quickly you lift your foot off the clutch pedal, the clutch engages the flywheel at a constant (slow) rate. In theory, it can save the driveline from shock, were an inexperienced (or immature) driver to dump the clutch.

I didn't realize your question was directed towards wsmeyer so... carry on.

[wsmeyer]

Because of this valve, no matter how quickly you lift your foot off the clutch pedal, the clutch engages the flywheel at a constant (slow) rate. In theory, it can save the driveline from shock, were an inexperienced (or immature) driver to dump the clutch.

No doubt that is it's purpose and why it is there, but I believe that it will allow a high enough flow rate that under normal operation of the clutch pedal it won't come into play.

William.

[nike001]

I don't think that a CDV delete is a deciding factor in having a destroyed engine or just a stalled one if your foot slips off the clutch on accident.

That being said, I just deleted mine and 1-2 shifts are awesome


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[UdubBadger]

^ agreed no chance


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[wsmeyer]

Very interesting post but I can't say I agree. I did not bleed the line when I installed the CDV, and it made a huge difference.

But if you didn't bleed the line then you've essentially done two things: removed the CDV, and introduced air into the system that is acting as a pneumatic spring. It isn't any different than a brake line where even a tiny amount of air can make a huge difference in pedal feel.

The only way to accurately compare with and without the CDV would be to bleed the line, get use to that, then remove the CDV and bleed the line again. Thus only changing one thing.

If I had known what I know now that's what I would have done. As it is I changed two things at once and while I feel a difference, it cannot be explained by the removal of the CDV valve because of the mechanics as I described above.

William.

[RITmusic2k]

These last few posts raise a lot of interesting questions.

William, I disagree with your conclusions as well, for a couple reasons.... I'm not, however, equipped to fully defend each of them. But if you'll pardon my doing so, I want to put a couple thoughts on the table:

First, the assertion that the difference reported is due more to the effect of bleeding the clutch system ignores all the reports of increases in clutch pedal responsiveness from people who removed their CDVs without bleeding - I count myself among these people. I accept that this is not a rigorous test because we changed two variables at once, but I'll also suggest that you can safely ignore it as a biasing factor. If anything, the introduction of air into the hydraulics will have a damping effect of its own and would only serve to reduce the effective increase in responsiveness that we're reporting. If air got in my lines during the CDV removal and I still experienced a significant improvement, then I can confidently expect there to be an even greater improvement by bleeding the lines.


The point you seem to be sticking to is the idea that the clutch pedal position is directly linked to the pressure plate position, and if it were, then your argument would stand, but I suspect -- and this is the part where I'm not fully capable of backing my argument -- that this is not exactly the case. We know that the clutch pedal position is not directly tied to the pressure plate, because if it were then the clutch pedal would stop immediately at the friction point. But the pedal keeps moving past this point as the diaphragm spring continues to release and pressure is increased on the clutch plate. This entire top half of the clutch pedal's travel influences the clamping force exerted on the clutch, but the clutch and pressure plate have already stopped moving in relation to each other by this point.

So with that in mind, I'm suggesting that a manual transmission without a CDV will behave more or less like you describe, where the clutch pedal position, pressure plate position up to the friction point, and the friction point itself are all directly related and 'fixed', so to speak. Adding a CDV, however, serves to uncouple the pedal position from the remaining parts of the system. I think, because of the huge mechanical ratio between the master and slave cylinders, installing the CDV can dramatically change the operation on the pressure plate while imperceptibly changing the way the pedal moves. Ergo, even though the pedal comes up off the ground just as fast as it did before removing the CDV doesn't mean that the behavior on the other end of the line isn't different enough to produce the change in responsiveness we're all experiencing.

[Johnmadd]

Great friendly debate guys, stick to your guns.

[nike001]

Just going to throw this in here:

The CDV delete for me was one of the best mods I've done yet.

[Rovert]

The CDV delete was the one mod that I didn't feel anything...LOL. Unless maybe that's just how I shift and I've got used to it. I'm not a power-slammer into gears. I try to keep my shifts as smooth to the drivetrain and ride as possible so I get no neck jerkers! Don't be rough if mom is in the car drinking something...it ends up very bad from my experience. LOL