Z4MC: What's a CDV?

[aestheticstorm]

I've been reading a lot on these forums about the nuisance of the CDV. What is it and why would BMW include this part if it causes so much shifting trouble? What purpose does it serve? Is it something I could remove myself or do I need the dealer to do it? Thanks in advance.

[zrdster]

The Clutch Delay Valve is supposed to dampen your clutch in such a way that it makes it difficult for you to dump the clutch upon launching the car. There are some schools of thought that it may shorten the life of the clutch as it causes you slip the clutch without trying... I can't speak to why BMW engineered it into the car, I'm sure they think there is some value to it....

You can replace it yourself if you are mechanically inclined and have a bleeder capable of bleeding ABS,

The dealer will not (likley) replace your CDC with a modified one... I suspect that they would say that it voids your warranty on the clutch...

Some folks here are much smarter than I about the mechanics of the device and I'm sure you will get better explanations of that part. You can also read a TON of information here if you search around for it...

[aestheticstorm]

I've read a lot that CDV sucks, but can't find much on why this is so.

[zrdster]

From my perspective, the clutch feels dampened...

[Zuzax]

If I ever get around to dealing with mine I'm going to just have it removed instead of putting in the fake one.

I would think that BMW has read enough about this on countless messageboards to know what to look for, and I think getting caught with a counterfeit part would kill more goodwill than just removing it.

Hell, they probably even have a Service Bulletin on it. They had one about the grey intake filter.

[wrh3]

OE CDV on left, modified one on right:

http://www.billswebspace.com/CDVZ4.jpg

The smaller hole slows down the fluid flow effectively slowing the reaction time of the clutch compared to driver input (and does slip the clutch which will increase wear). I think BMW did this to reduce wear/tear on the drivetrain, at the expense of the clutch, with abuse and/or inexperienced manual trans drivers.

Some good info here: http://www.zeckhausen.com/cdv.htm

[Dammmittt]

Bill's correct. The CDV just makes the car shift slower than it should. After time you get used to it, even if it does shorten the life of the clutch...:dunno:

[zrdster]

All good points above... I've been told by my dealer that they would replace one clutch under warranty. If you need it replaced again then it is abusive shifting, according to them... So, BMW must know that it could lead to premature clutch wear but they anticipate that it could happen no more than once in 50K miles... IMO anyway...

[jmillet]

I've been reading a lot on these forums about the nuisance of the CDV. What is it and why would BMW include this part if it causes so much shifting trouble? What purpose does it serve? Is it something I could remove myself or do I need the dealer to do it? Thanks in advance.

When your Z4 M Coupe finally arrives and you've had a chance to experience the hip-hop clutch action drop me a PM and we'll get together so you can drive my CDV-less in Seattle Z4MC and see how a real clutch should function.
Deleting the Clutch Delay Valve was the first thing I did after having Scotchgard clear mask applied.
If you have the tools (flare wrench and Motive Power Bleeder) and can get the front of the car jacked up high enough then it's a relatively simple job.

[cmichaelo]

Seems there's three different tools for bleeding the brakes.

The pressure power bleeders seem to be the most talked about here, like Motive.

But what about the vacuum bleeders that connect to the bleeder screw and essentially suck the brake fluid out instead.

And third, there's the poor mans solution which is basically a hose with an integrated valve with opens upon depressing the clutch pedal and which closes upon releasing the clucth pedal.

Are any of these not up to the job or are they not reliable enough?

(Just received my Zeckhausen CDV in the mail...he he.)

Michael

[reidconti]

All good points above... I've been told by my dealer that they would replace one clutch under warranty. If you need it replaced again then it is abusive shifting, according to them... So, BMW must know that it could lead to premature clutch wear but they anticipate that it could happen no more than once in 50K miles... IMO anyway...

It's pretty hard to toast a stock clutch in 100k miles. Forget two clutches in 50k.

[jmillet]

Seems there's three different tools for bleeding the brakes.
The pressure power bleeders seem to be the most talked about here, like Motive.
But what about the vacuum bleeders that connect to the bleeder screw and essentially suck the brake fluid out instead.
And third, there's the poor mans solution which is basically a hose with an integrated valve with opens upon depressing the clutch pedal and which closes upon releasing the clutch pedal.
Are any of these not up to the job or are they not reliable enough?
SNIP
Michael

I've tried every bloody bleeding method known to man and find the power pressure method to be the most idiot proof and reliable. The old fashioned two person pump and bleed method as well as the Mityvac suction method leave open the opportunity to introduce air into the system. With the pressure method it's virtually impossible to introduce air into the system unless you let the reservoir run completely dry.
Using a turkey baster or Mityvac I suction as much of the old brake fluid out of the reservoir as possible then fill with fresh fluid, attach the Motive Power Bleeder containing fresh fluid, pressurize to 15-20 PSI and bleed away checking the pressure periodically to maintain at least 15 PSI.
BTW I've not run across the "integrated valve" device you mention.

[cmichaelo]

I've tried every bloody bleeding method known to man and find the power pressure method to be the most idiot proof and reliable. The old fashioned two person pump and bleed method as well as the Mityvac suction method leave open the opportunity to introduce air into the system. With the pressure method it's virtually impossible to introduce air into the system unless you let the reservoir run completely dry.
Using a turkey baster or Mityvac I suction as much of the old brake fluid out of the reservoir as possible then fill with fresh fluid, attach the Motive Power Bleeder containing fresh fluid, pressurize to 15-20 PSI and bleed away checking the pressure periodically to maintain at least 15 PSI.
BTW I've not run across the "integrated valve" device you mention.


I hear what you're saying. With a pressure bleeder there's constant pressure in the brake lines. Thus while the bleed screw is open this can only result in fluid and air going out of the system.

The "integrated valve" is the $5 hose you can buy at any autoparts store. It's a ~2ft transparant rubber hose with a short black soft rubber piece at one end which fits snuggly over the bleed screw. Inside the black rubber piece is a valve which opens upon pressure and which closes upon lack of pressure (such as when letting the clutch pedal return to its neutral position.

The one that I have is called the "One-man brake bleeder". I've used it to bleed brakes with no problems multiple times.

Btw, even if there is a couple of air bubbles in the clutch system, will this really make a difference on the clutch operation? And is there any chance the brake system can get contaminated with air bubbles from the clutch system?

Michael

[jmillet]

SNIP
The one that I have is called the "One-man brake bleeder". I've used it to bleed brakes with no problems multiple times.
BTW, even if there is a couple of air bubbles in the clutch system, will this really make a difference on the clutch operation? And is there any chance the brake system can get contaminated with air bubbles from the clutch system?
Michael

Is this the device you are referring to? http://www.toolking.com/otc(divisionofspxcorp.)_otc4599.aspx

Brake fluid doesn't move through the lines like coolant in the cooling system so air in one line can't migrate to another part of the system.
Air in the clutch lines or slave cylinder will cause the clutch pedal to feel "soft and spongy". Pressure bleeding coupled with numerous depressions of the clutch pedal will purge air from the system. Just letting the system sit overnight will allow gravity to do its job and the lighter air will work its way up through the lines and into the reservoir.

[dwm]

I like speed bleeder valves on the brakes. Should be possible to put one on the clutch slave cylinder too, but I don't know what size would be used there.

[cmichaelo]

Is this the device you are referring to? http://www.toolking.com/otc(divisionofspxcorp.)_otc4599.aspx
Not the same brand, but otherwise it looks identical to what I have.

Just letting the system sit overnight will allow gravity to do its job and the lighter air will work its way up through the lines and into the reservoir.
Are you saying that even if I don't do any bleeding at all, the air bubbles will eventually migrate upwards in the clutch system and finally reach the reservoir?

If that was true, then why does the clutch system need bleeding? Or did I misunderstand what you said?

Has anyone experienced spongy feeling in their clutch due to air in the system?

I'm asking because I'm not convinced that air in the system would cause a spongy feeling in the clutch. I'm saying this based on these assumptions: 1) the pressure in the clutch system doesn't get near as high as in the brake system and 2) the pressure in the clutch system is constant upon depressing the pedal.

Michael

[Ron Stygar]

http://www.bimmerfest.com/forums/showpost.php?p=482157&postcount=1

[cmichaelo]

http://www.bimmerfest.com/forums/showpost.php?p=482157&postcount=1

What has your experience been with this tool, Ron? Do you recommend this over pressure bleeding?

Michael

[Ron Stygar]

What has your experience been with this tool, Ron? Do you recommend this over pressure bleeding?

Michael

Been using it for a few years. You still use the pressure bleeder.