[Nezil]

I removed my CDV last night. Getting the slave cylinder off and removing the CDV was easy, but I ended up not going to work today because I was unable to bleed the clutch system!

I'm going to post my experience in another thread, because I think it would be valuable to the community to understand the issues surrounding clutch bleeding, and the root cause of the bleeding issues. There is much mis-information out it being essential to reverse bleed, but once you understand the root cause of the issues several ways to bleed become apparent.

As for the improvement without the CDV... I've only driven the car twice, but I'm already going to say that the improvement is MASSIVE!

Every car I've had since I started driving 24 years ago, has been a manual, with the exception of my previous car that I had for 4 years. I'm pretty familiar with manual gearboxes then, but I was never really satisfied with the gearbox in the M2, but couldn't put my finger on why... Now, having removed the CDV, I can say that it was 100% the reason why, but I'll dive into the actual differences a little deeper for anyone on the fence.

With the CDV in place, the pedal position and time at which the clutch engages is unpredictable. With time and experience, you can try and learn the behaviour, but I still found that I'd get jerky shifts sometimes, particularly in slow moving traffic where you're either stopping and starting, or shifting back and forth between 1st and second at low speeds. I also felt that pulling away it was difficult to modulate the clutch as I'd like to. It wasn't jerky, but difficult to do quickly and smoothly.

Everything I've said so far was with auto-rev match enabled... with it disabled, things were far worse! The CDV effectively delays the engagement of the clutch, and if you rev-match manually, you have to make sure to rev higher than you really need, because the clutch isn't going to bite when you lift off the pedal, because it's delayed.

If you choose not to rev match, things get awful fast. The delay caused by the CDV lets the revs drop far too much as you downshift, and even if you try to slowly let the clutch bite in, that doesn't happen smoothly.

Before I removed the CDV, I'd assumed that these behaviours were due to the tune of the engine, or an overly aggressive sports engine / flywheel / clutch combination, but I now know that's not the case.

One last point... I've heard from non-M owners that the CDV causes the clutch to slip between shifts. I never found this to be the case with my M2; the shifts were delayed and sometimes not smooth, but there wasn't any slippage. This leads me to think that the M-series clutch / flywheel / CDV combination might have different issue characteristics for M owners than non-M owners. It's probably worth doing for both M and non-M, but if you're getting slipping with the CDV, my comments above may not apply.