Clutch Delay Valve

[macfly]

A great post from Dave Zeckhausen......

This is the clutch delay valve (CDV) that haunts the E39 5-Series owners (except M5) by screwing up their shifting. I've already personally removed over 150 of these and mailed out modified CDVs to more than 100 other folks so they could do it themselves. We figured out the CDV might be the culprit to the E39 shifting woes when it was noted that the M5 didn't have one. That's why I was so astonished to find one in the Z8.

The CDV on the Z8 had the appearance of the one that is shown 2nd from the left in the photo below. It looks just like the one in the 540i 6-Speed and a quick check of the BMW parts CD confirmed that the Z8 and 540i indeed share the same part.

For a complete description of the CDV, it's operation, and why it's bad, you should check out my CDV web page at: http://www.zeckhausen.com/CDV.htm

[macfly]

The new 'Clutch no-Delay Valve' is absolutly fantastic, it makes the clutch so instinctive, and immediate.

I didn't realize what bad pedal/clutch action the standard one had untill I made the swap. I can also 'feel' that the clutch life will be doubled, it reduces any high friction slip to mere milliseconds. This is a little upgrade that make a very big difference, and in brisk driving it is an absolute joy.

[Rjay]

Did you install yourself? How difficult? Are there any downsides you know of in doing this mod? thanks

[macfly]

you really need the car up in the air to do it, so I took it to my shop. Once it is up in the air it is a very fast job, about an hour to 90 mins work, including bleeding the clutch system.

I can't see or feel any reason why this would be bad, the clutch engages much more quickly and crisply, eliminating the drag on the friction surfaces that the standard set up causes. Thus I think the clutch will last much longer, and you won't risk the getting cooked clutch sydrome on fast get aways which several board members have mentioned.

The fact that BMW removed it from the much heavier M5 suggests they were aware of it's negative imapct on wear and performance. Why they decided to put it in the Z8 beats me, especially now I've driven without it. I find the quicker clutch greatly enhances the sporting nature of the car, it is a little mod, but well worth doing at your next full service.

[Norcal]

After I get my clutch replaced (hopefuly under warrantee)

[siliconvalleyman]

An excuse for why I seem to have lost so much of my racing ability with this car. I had been wondering why my shifting skills honed with 5 years of SCCA FM racing were seemingly lost when driving my Z8. This makes a lot of sense and I will make the mod since the clutch action is kind of dorky.

After I installed my shortshifter, I expected more precise shifting. Now I know why that did not happen. I also concur with the belief that the clutch is likely to see significantly more abuse with this valve. I already had my clutch replaced once.....

[macfly]

To those of you who have replaced the CDV, a few questions:

1) Are you obtaining a CDV directly from Zeckhausen Racing or are you removing yours and opting for the 48 hour turn around fix of your original CDV? I ordered mine, it was an easy swap once the car is up in the air, took my shop less than 60 mins to do the whole thing.

2) It seems difficult to do it yourself, so would it me easier to have the local BMW dealer do the work? The hard part is getting under the car, so I would say yes, for sure take it in.

3) Do you know how this would affect the warranty on the parts of the clutch assembly and hydraulics that ARE warranty items? ':confused:' It shouldn't make any difference to anything in the warranty. It will actually save the clutch, and though it could be argued it will put more strain on the transmition you'll be making smoother, crisper changes once it's done, which will ease wear. Honestly you'd have to be driving like a hooligan for the entire warrranty period to have even the slightest chance of any transmission issues showing up.:D

[brownie]

I am a proud owner of a '01 silver/black and a new poster to the board. After several months of balky shifting, I am planning to remove the CDV and have a question --- to those of you that have done the modification, have you removed it entirely or replaced it with a modified valve? I read the Zeckhausen discussion on the subject and the reasons given to replace it with a modified valve don't seem all that compelling vis a vis removing it entirely.

[macfly]

is simply because when you remove it you need to fill the gap it leaves, and not stress the hydraulic line.

If you, or your mechanic, are handy with a drill you can simply drill out the restrictor inside the unit. The CDV is simply a hydraulic fluid restrictor that is achieved by a ring that's cast into the body of the unit. It's easy to just drill it out, and put the same unit back in.

[DZeckhausen]

is simply because when you remove it you need to fill the gap it leaves, and not stress the hydraulic line.

If you, or your mechanic, are handy with a drill you can simply drill out the restrictor inside the unit. The CDV is simply a hydraulic fluid restrictor that is achieved by a ring that's cast into the body of the unit. It's easy to just drill it out, and put the same unit back in.Assuming your Z8 is out of warranty, the only reason to use a modified CDV, rather than just removing the old one, is for ease of installation. If you remove the CDV and don't replce it, you will need to put a slight bend into the hydraulic line to make the fittings line up properly. It's not a major bend and there's virtually no risk of kinking the line. The issue is getting the angle just right so you don't cross-thread the fittings. When I do a Z8, I simply use a modified part, since it's not worth the risk of damaging the threads and leaving the car undrivable until I replace the entire clutch line.

As for modifying the valves yourself, sure that's fine. Just don't use a drill. There's a pocket inside the valve and drilling through it will leave fragments behind, including bits of a steel spring. If you use a drill bit large enough to get all this junk out, then you'll enlarge the tapered seat on the female end and you'll enlarge the opening on the male end, such that the CDV won't be able to form a tight, leakproof seal. The CDV does not seal by the threads. It seals by the mating, tapered surfaces on the ends. If you remove most of that mating surface with a drill, you end up with a leak under pressure. You might not notice it during installation, but you will notice it a month later when your clutch pedal goes to the floor and stays there.

I modify the valves using a dentist's pick to pull out the spring, then I use a skinny centerpunch and hammer to tap out all the guts, while being careful not to damage the thin, tapered seat on the female end. Finally, I blow compressed air through it, then check again with the dentist's pick to feel around inside for any remaining bits. I've done over 1,000 of them, so I've become pretty good at it. But I did destroy a couple of them when I was experimenting.

[macfly]

Thanks for the explanation Dave. I used one of your units, and didn't notice any springs or pockets in the one I threw out, but I only gave it a quick glance, and thought the 'valving' was achieved with a simple restriction ring cast into the unit.

[DZeckhausen]

Thanks for the explanation Dave. I used one of your units, and didn't notice any springs or pockets in the one I threw out, but I only gave it a quick glance, and thought the 'valving' was achieved with a simple restriction ring cast into the unit.It's a 1-way valve that restricts only during the release stroke of the clutch. The parts look like this:


http://www.zeckhausen.com/images/Modifications/cdv/valve_and_spring.jpg

Although you'll never actually see the parts whole, since the center punch breaks the valve into little chunks.

[Dogsbreath]

Thank you Dave Zeckhausen !!!

I just replaced my CD valve and it made a huge difference. The car is so much smoother. I did the work myself in about 30 minutes including the road test. This is an easy install on the Z8.

I also installed the upgraded transmission mounts from Dave Zeckhausen. They are a little difficult to install as the exhaust pipes are right in the way of the 2 aft transmission brace bolts but it is not impossible. I had a TR3 for about 20 years so I can be a contortionist but I am not so used to it on the BMW. The mounts definitely improved the feel of the car especially during spirited driving.

I recommend both these products.

Dave

[macfly]

another excellent and very cost effective upgrade that actually makes a difference. The easiest time to put them on your car, or have them put on, is when you are swapping your mufflers over to the Eisenmanns.