What is the clutch delay valve(CDV)

[daneharrigan]

I see it mentioned in the 20k clutch burnout thread. Is that the mechanism that keeps the car from rolling back?

If my post number doesn't flag me as new, my type of questions should :^)


Thanks in advance,


-Dane

[jeremyc74]

The Clutch Delay Valve (CDV) is a small restriction that's in the hydraulic line between the clutch pedal and the slave cylinder that releases the clutch.

It's a one way check valve that allows full flow as you're disengaging the clutch, but creates a restriction to the flow as you release it, causing the clutch to re-engage more slowly.

From BMW's perspective it is probably there to reduce shock on the clutch, pressure plate, and driveline that's caused when someone dumps the clutch. From a driver's perspective it sort of creates a slight disconnect between what your foot is doing and what the clutch is doing, and it can make it harder to get a smooth shift, especially going from 1st to 2nd. It would seem that it would also have to create additional slippage during a hard shift under power, which is bad for the life of the clutch.

The clutch is a wear item, so BMW probably figures it's better to reduce the life of the clutch slightly than increase the risk of an actual failure due to the shock of "dumping" the clutch.

[Absorber]

[mineo77]

do a google search on it too...you will find some interesting info about the clutch 'lock' valve.

[jeremyc74]

Originally Posted by mineo77

do a google search on it too...you will find some interesting info about the clutch 'lock' valve.

Lock?

[mineo77]

Originally Posted by jeremyc74

Lock?

Yep, in the BMW part list this valve is called a 'clutch lock', NOT a clutch delay valve. If you call BMW and ask for a clutch delay valve, likely they will have no idea what you are talking about.

here is some info:
http://www.zeckhausen.com/CDV.htm

I love this mod..i must do for sure

[jeremyc74]

Originally Posted by mineo77

Yep, in the BMW part list this valve is called a 'clutch lock', NOT a clutch delay valve. If you call BMW and ask for a clutch delay valve, likely they will have no idea what you are talking about.

Must be some weird translation for the one-way restriction that's in there.

[daneharrigan]

@jeremyc74 thank you very much for the information

@mineo77 and to you for the "clutch lock" explanation

@Absorber thank you as well, for the unnecessary picture, it was funny

[larryn]

Originally Posted by daneharrigan

@Absorber thank you as well, for the unnecessary picture, it was funny

Most thorough and best response to your question though, in my opinion.

[daneharrigan]

@larryn But what would be the point of joining a forum if not to start conversation? A member is not obligated to reply to every thread on here so I appreciate the responses they take the time to make. A "find it yourself" type response doesn't give the best first impression. Luckily my thread of BSM vs. JB was my first impression and with excellent forum members.

I've gone way off the original topic though. Thanks all again for the information! I always appreciate it!

[larryn]

Originally Posted by daneharrigan

@larryn But what would be the point of joining a forum if not to start conversation? A member is not obligated to reply to every thread on here so I appreciate the responses they take the time to make. A "find it yourself" type response doesn't give the best first impression. Luckily my thread of BSM vs. JB was my first impression and with excellent forum members.

I've gone way off the original topic though. Thanks all again for the information! I always appreciate it!

Well, join the forum, but don't be lazy and ask the same question that has been asked a hundred times already. The search function is there for a reason.

Also, nobody is saying that you should not join the conversation. Feel free to bump the old threads, if they don't completely answer your question, or you want to continue that same conversation. Just think of what a mess a forum would become if every response was a new thread.... Not meant as a hand slap, but "teach a man to fish"...

[Steve_in_NH]

I replaced this (as a DIY) in my 2001 3.0l Z3 and the driving was like night and day. From hesitant and jerky shifts to smooth as silk (the way they were supposed to be). Part cost $35.00.

[jeremyc74]

Originally Posted by Steve_in_NH

I replaced this (as a DIY) in my 2001 3.0l Z3 and the driving was like night and day. From hesitant and jerky shifts to smooth as silk (the way they were supposed to be). Part cost $35.00.

You don't really even need to buy the part. You can knock the guts out of the one from the factory pretty easily and just put it back in.

[larryn]

...or just bypass the CDV altogether. Remove the CDV, and the two open ends fit together.

[jwellsiii]

I'll bite: "The CDV is an evil little bastard that makes you think you should have bought the paddle-shifters".