CDV Delete

[MrPT]

Its a pretty straight forward job well within the DIY capability.

http://z4-forum.com/forum/viewtopic.php?f=25&t=1227

...if you have a drive/garage, axle stands, the required spanners, a jack, can do a solo re-bleed and aren't fussed about the peace of mind of getting it done at a trusted local garage. Agree that it is worth doing it yourself otherwise!

Point taken :wink:

I'm just jealous Would give my left nut for a decent sized garage.

Re. the CDV removal potentially allowing/masking damage; there is of course a risk, with an associated financial penalty. But, given the likelihood of something happening and the fact that you can also put a price on never quite being happy with the 1st-to-2nd shift of your £10k+ sports car, it is an acceptable risk for many people.

Not convinced about the explanation of clutch judder though. Surely it's also caused by over-aggressive clutch engagement? If not, then pretty much every car I drove when I was 17 had clutch issues.

 

[mad4slalom]

sorry stu thought you had written that post but it was alpsad . , meant to say it would be interesting to see what zeckhausen racing who do the modified cdv's take is on this, or maybe rogue engineering.

 

[edd_jedi]

Agree with Stuart to be honest. It's amazing how many DIY mechanics think they know better than the billions of pounds BMW spend on research :lol: I haven't noticed any judder at all in my Z4, dare I say there is a problem with your clutch or clutch control!?

 

[StevenH72]

Surely a clutch stop would be a better way of avoiding judder?

 

[MrPT]

Agree with Stuart to be honest. It's amazing how many DIY mechanics think they know better than the billions of pounds BMW spend on research :lol: I haven't noticed any judder at all in my Z4, dare I say there is a problem with your clutch or clutch control!?

Are you sure your CDV is still there and not modded?

 

[edd_jedi]

I guess it's possible it has been removed, but not that I know of. Is there any easy visual check?

 

[Machine monkey]

I guess it's possible it has been removed, but not that I know of. Is there any easy visual check?

You have had lots of BMWs though right? So you might have just mastered there clutches. But I would have a look at the post there are pictures. But you should be able to see the valve.

I hate the 1st 2nd gear changes and trying to pull away quickly just dose not feel right!!

 

[MrPT]

I guess it's possible it has been removed, but not that I know of. Is there any easy visual check?

It's in this area:

Here:

It's the nut /collet closest to the metal bracket.



Sent from my GT-P6810 using Tapatalk 4

 

[edd_jedi]

Great, thanks. Will try and have a look later. I'm pretty sure the first owner of the car wouldn't have done it, but the previous owner may well have done!

 

[MrPT]

Great, thanks. Will try and have a look later. I'm pretty sure the first owner of the car wouldn't have done it, but the previous owner may well have done!

It could be there still, with the innards removed, in which case you can test it by getting someone else to drive your car aggressively off the lights.

I don't think this is a right/wrong debate. It's just a choice you can make if you are comfortable with the potential consequences - a bit like switching to non-RFTs; again, where the majority of people are happy with the change, but some don't think it's worth it for the compromise in convenience/safety.

Sent from my GT-P6810 using Tapatalk 4

 

[Zeld4]

This...

Engineering and dynamics (vibration) background here, and a full-on understanding of this system as its been in use for donkeys years and is known for problems, so bear with this short explanation...and I know there has been plenty of uneducated rambling on this elsewhere, but that is a problem with forums and incorrect info, sadly :|

The CDV is only in the system to prevent lash into the DMF if the clutch is released rapidly and/or without control. The CDV slows the fluid flow on clutch release via its restricting orifice, hence automatically reduces the lash in the system, gives a 100% repeatable clutch release rate and prevents accidental (or careless) damage to the DMF. Removing a CDV valve whilst being the 'manly' thing to do, is in effect putting your DMF at risk if you make an error with your clutch control. It has NO effect on clutch judder per se, only its apparent severity. Clutch judder is a result of a high and hot spots due to non-flatness and localised heating on the clutch plates. The hot spot comes from local heating friction during clutch engagement, and may be (for example instance) a slight inbuilt and within tolerance misalignment between plates on take-up (there is after all, a 360degree arc of take-up, so a potential 1 in 360 chance of matching high and hot spots at instant of drive take-up). The high and hot spot interaction results in a grab-release-grab-release of the DMF drive and friction plates, and this causes the DMF drive springs to oscillate at their undamped natural frequency (imagine fixing a rope at one end and flicking the other repeatedly and seeing the waves it sets up). That shakes the car to buggery as the drive is taken up and released in pulses..... The undamped oscillation then causes the springs to clatter their guides and housing and reduces the lifespan of the springs, and can crack the casing and/or flywheel itself...which is a right-off of the DMF. If you remove the CDV on a DMF with a minor issue, you may improve the engagement slightly as the plates will come together faster, and any fluctuations pass more quickly (basic dynamics) but still exist. That is masking, not fixing the fault.

Friend of mine works as a main dealer service manager. He's lost count of the number of DMF's that they get in with 'slight judders' and on opening the joint, bits of DMF fall out of the bell housing. I recently had in my hands a 9k-miles old DMF which had been run without a CDV. It was trashed. £1200 again please, sir, for the benefit of giving you back your drive. Leave the CDV in: BMW put it there for a bloody good reason. If the clutch judders, it has a DMF problem. Full stop.

From a personal POV, I would never buy any used car from any manufacturer where I thought the CDV may have been removed by a previous owner unless the DMF had been exchanged just prior to my purchase.

But as in all things, your car your choice.

Is the CDV really there to just reduce lash on to the DMF? I thought it was also there to reduce sudden power surges in to the transmission too.
I know two people who had there DMF replaced recently on BMW diesels and both still had their CDV intact.
I think the problem is the DMF and the CDV are two solutions to the same problem that don't work together. Fo a start the CDV does not operate consistently and from time to time will literally not let the clutch out. It can in fact cause lash on to the DMF. You could be the perfect driver (I'm not) and the CDV could still mess up your gear changes. And the fact that so many DMF's go when the CDV is still connected doesn't add up to the CDV protecting the DMF.

It's all about BMW trying to avoid warranty claims. The DMF and the CDV both reduce sudden forces on to the the drive train, thus making damage less likely. Gear box and engine are warranty covered parts. The DMF is not. The DMF is a cash cow for BMW service centres because it's badly engineered and doesn't work well with the CDV, and the CDV doesn't work well with fly by wire throttles.

So BMW design something to save them on warranty claims that falls apart and doesn't work well and is not covered under warranty.
That's double bubble for them!!

 

[k31ron]

Agree with Stuart to be honest. It's amazing how many DIY mechanics think they know better than the billions of pounds BMW spend on research :lol: I haven't noticed any judder at all in my Z4, dare I say there is a problem with your clutch or clutch control!?

I'm not sure i would have your level of faith in the outcome of "BMW's Billions of pounds of research" my car has had 2 expensive roof motors replaced due to inherent poor design .... there's always room for improvement and plenty of mistakes are made regular made regardless of budget the most obvious manifest in a long line of recall's and service bulletins issued by all manufactures

 

[MrPT]

Why is it a "delete"? :?

 

[Carsonking]

Well 24 hours and no problems yet, he he. A passenger commented on how much smoother it was when changing gear and I hadn't told him I'd had it done, I'm not changing mine back. If you don't drive like an old maid and you have the ability to change gear properly, it's a no brainer. Not one person has come back and said they have had the problem, let the old maids embarrass themselves at traffic lights.

 

[mad4slalom]

carsonking, did you modify yours or remove it, as i modified mine and its better but i a thinking of removing it altogether as it is still not as a normal clutch. and is still part restricted due to the smaller apeture. i think i am with you on this one , havent heard enough evidence re the dmf/cdv yet to refit it.

 

[mad4slalom]

the only sure way to be sure a previous owner did not modify the cdv is to remove and inspect it. I am sure an unmodified cdv is harder on the clutch as when you execute a fastish getaway the clutch rides / slips for the period that it takes for the clutch to engage which is longer than if the valve was not present, with no valve the clutch engages as soon as your foot is off the pedal, the cdv to my understanding is to protect the drive train ,ie gear box and diff, never, heard of it protecting the dmf as the dmf is supposed to protect the clutch. aaarrrgggghhhhh now i am confused !!

 

[original guvnor]

Put it this way, judging by the way my car drives, if mine has been modified or removed by a previous owner they were wasting their time!

 

[GregZ4]

I've asked my local garage what he thinks by email. See what he says and what he quotes as I'm ham fisted when it comes to spanners.

Still not sure why it's even the reading the posts above but I am sick of bouncing away from lights when I try to engage anything less than 3rd quickly. I'm not even ramming the revs, it just doesn't lend itself to a slick change........

 

[Stuart Truman]

a lot of vehicles especially fords have dmf problems, rattles, breakages etc and dont have cdv 's fitted in the sytem.

I think this makes Ade's point. No CDV and a lot of known problems with DMF's

I wonder how many people on here are re ordering cdv's from the dealers already. when stuart first got immie he mentioned that he wasnt going to change the cdv as he just got used to it but didnt mention the dmf at all then, just wonder where this story came from.

No flak from me, if you trawl back over my posts I said the same about my Alpina. I asked about the notchy shift from first to second when I first joined the forum. A lot of people suggested a CDV delete, I looked into it and decided against. That was after advice from engineers like Ade and other owners on the Alpina Register.

The forum is here for debate and advice, that's a good thing. I'm offering up an alternative point of view along with a rationale as articulated very clearly by Ade.

The first to second shift is nothing to do with the clutch in any way, it's gearbox mechanicals and a trait of the 'box. If it was the clutch you'd have an issue with all shifts. Judder is exactly as he describes it.

And I don't drive like miss daisy, I got IMmie because a wanted a rawer car than #69, I heel and toe and "press on" as the mood takes me. Like all cars, Zeds have characteristics and you love or loathe them, and make changes to those things you don't like.

If you want to remove your CDV then do so, have fun. But do it with your eyes open, in full awareness of the possible risks and rewards.

 

[exdos]

The Z3MC doesn't have a CDV and I've not heard of any problems with clutches and flywheels and that car is now 11+ years old and I've seen all manner of standing starts with different Z3MCs!.