Z4-forum.com

Machine monkey wrote:Ok i dont have a full grasp so this might not be 100% correct.

But my understanding the CDV is to prevent harsh and sudden shocks causing damage to the DMF. From surges of power from say the clutch being drooped or poor gear changes. Its sole purpose is to protect the DMF from shock.

Yep that's it basically slows down the clutch action

Posted from Tapatalk

CDV has a restrictor plate in it. It means that no matter how quickly you release your foot from the clutch, the clutch will engage at a constant speed.

So, when the clutch initially bites, it will take a split second longer to be fully engaged. This makes changing from 1st to 2nd gear very difficult to do smoothly.

When you remove the valve, it's like driving a normal car again.

... just don't dump & bounce the clutch badly in first after you have it done, can end up shattering the flywheel on extreme instances.

My 3.0 was quite smooth between 1st & 2nd after CDV removed, one of my fav & early mods

Adamski wrote:CDV has a restrictor plate in it. It means that no matter how quickly you release your foot from the clutch, the clutch will engage at a constant speed.

So, when the clutch initially bites, it will take a split second longer to be fully engaged. This makes changing from 1st to 2nd gear very difficult to do smoothly.

When you remove the valve, it's like driving a normal car again.

Machine monkey wrote:Ok i dont have a full grasp so this might not be 100% correct.

But my understanding the CDV is to prevent harsh and sudden shocks causing damage to the DMF. From surges of power from say the clutch being drooped or poor gear changes. Its sole purpose is to protect the DMF from shock.

Thanks guys

I've left the CDV in place on the basis that I haven't noticed an issue and it's there for a reason, if BMW could save a few quid and delete it I guess they would? The only time I get up-changes a bit off is immediately after hitting the sport button as the throttle response is much sharper but you soon adjust. Not sure how CDV delete would affect this reaction?

Machine monkey wrote:Ok i dont have a full grasp so this might not be 100% correct.

But my understanding the CDV is to prevent harsh and sudden shocks causing damage to the DMF. From surges of power from say the clutch being drooped or poor gear changes. Its sole purpose is to protect the DMF from shock.

Exactly right

This is another "can o' worms" topic. Ultimately your car your choice. The effect on an M is apparently less than the non M, but it doesn't take too long to adjust to driving style.

Can anybody quantify how long the stock CDV "lengthens" catch time? Is it more on the verge of milliseconds or is it more substantial?

Can anybody quantify how long the stock CDV "lengthens" catch time? Is it more on the verge of milliseconds or is it more substantial?

There is also the argument that due to the delay in the clutch being released that there is an increase in clutch wear.

One of the best mods I did on my old car, but as above not so noticeable on the ///M.

Deleting it totally transformed my M, I am still on cloud nine with this mod, 8 days after removing it and it feels like a different car. I can't stop grinning and love the smooth gearchanges as after six months of ownership I was still unable to completely drive around the CDV.
I don't want to be too evangelical about this but DO IT!

Silver grey Z4MC
Mods: Strongstrut 3 piece / CDV delete / Stormworks ST1 gearknob / clutch stop / stubby / ipod integration / LED interior / Magnaflow custom exhaust

The beauty of the E89 setup is, if you don't like the feel after removal, its easy to put the valve back in place, its just a push fit with clips.
Unlike earlier version requiring the drilling out of the valve or similiar.

I,ve misplaced the valve, otherwise would have a closer look.
Basically i think its gives full flow on depressing the clutch, but delays the release by restricting the flow through a smaller orifice, so the clutch plates close more slowly giving a constant closure rate.

Unfortunately in the winter i think the hydraulic fluid is a bit more dense so doesn't flow as easily giving me the judder on take up.
Perhaps the reason for the wiggly metal pipe to warm the fluid up a bit in winter?
Perhaps they had a load of wiggly pipe work to get rid of!

flybobbie wrote:The beauty of the E89 setup is, if you don't like the feel after removal, its easy to put the valve back in place, its just a push fit with clips.
Unlike earlier version requiring the drilling out of the valve or similiar.

No drilling out required on the earlier version... on the e85 the CDV just unscrews and you put the hose back without it then bleed.

The curly pipe is purely to aid installation during construction.

Can anyone tell me if it's as straight forward to do as the images at the start of this thread on an e86 3.0?

That's one of the great things about a forum like this for new members and owners of the car. I've been thinking about the awful gearchange particularly when going from first to second and have been trying to drive round it since I collected my car. A quick search through the 'new posts' after a couple of days away and this pops up. Really helpful.