[FieldingMellish]

Time-saving Executive Summary: CDV Replacement? Just Do It!

Ok, now the details. Had my CDV (Clutch Delay Valve) replaced today by Anthony at Speed Religion. As usual, great, corteous, highly professional service. And Anthony provides such a stark contrast with BMW techs I've dealt with in the past: he actually takes the trouble to explain to you how things work, and how components (eg. clutch, gears, flywheel etc.) interact. You could learn a lot from just chatting to him!

Most importantly though, getting rid of that damn CDV has had even more of a positive effect than I expected. And I was pretty hopeful since I'd driven Ant's SR3 and thus had a preview of the effects of replacing the CDV and restoring the operation of your clutch to normal, easy use.

Ant did stress that "this isn't going to transform your car..." and I understand and respect his reasons for saying that, but from my perspective that's exactly what it has done, it has *transformed* my car, or certainly it has transformed the experience of driving my car, it's transformed the process of changing gear from an annoying chore into what it always should have been, i.e. something you really don't need to think about. In fact it's now a pleasure to change gear!

Gone is that gloopy, soupy, indistinct clutch action. Gone is the utter vagueness of clutch engagement. Gone is the jerky, jarring feeling of shifting up - or down - through second gear. And as a bonus, mostly gone is the heaviness of the clutch pedal, the removal of the CDV having significantly lessened teh resistance felt on releasing the pedal.

Restored is the sense of a 'bite point'. Restored is the ability to change gear smoothly. Restored is my confidence in being able to pull out from an intersection and change gear quickly and non-frantically.

And these are just my initial impressions. As Ant said, it will take a wee while to fully get used to the new, vastly improved clutch operation.

In short I would very strongly recommend this procedure to anyone who is suffering with the jerky gear shifts and vague bite point that the CDV causes. It's like having a kidney stone removed - while you wait! An incision is made, the offending object is removed, a replacement valve inserted, fluid is drained, the patient is sown up again, no pain or distress is endured. In fact, I might ask Ant to send me my old CDV so I can preserve it in a jar of formaldehyde, maybe keep it on a shelf in the study - to ward off evil spirits.....

Thanks again, Ant. My car is so much more enjoyable to drive now.

[NFS]

Glad to hear that this has improved things.

[G33]

Mines better but i wudnt say a complete night and day transformation! clutch is lighter tho SSK next i think that will improve shift times no end i hope!

[R4R]

the Z4 is affected in the same way.

get rid of the CDV and stop kangerooing up the road

[PeteJ]

I sense a trip down south coming up!!

[dxb335d]

Why would BMW install this CDV if its frustrating for the driver of the ''Ultimate driving machine''

[FieldingMellish]

Originally Posted by dxb335d

Why would BMW install this CDV if its frustrating for the driver of the ''Ultimate driving machine''

It is hard to believe BMW would want that to be how their clutch action feels.

Well, as has been said [i won't quote him], BMW are happy to put pressure on the clutch to save the drive train, seeing as they won't replace a clutch under warranty (after whatever mileage etc.) So to make a saving they are happy to sacrifice drive quality.

I can tell you, it makes a big difference, getting rid of that CDV. It's roughly analagous to the runflat tires, at least in terms of the difference it makes.

How is your clutch, Carlos?

[R4R]

Originally Posted by dxb335d

Why would BMW install this CDV if its frustrating for the driver of the ''Ultimate driving machine''

Carlos it to make sure that if somebody decided to wind the engine up to 6K and dump the clutch the fluid running back from the slave cylinder to the master cylinder is restricted.

this causes a progressive application of the clutch to the drive plates etc. thus toasting the clutch and saving the drive line from shock.

there hope that helps.....

Dario

[TMP]

Originally Posted by R4R

this causes a progressive application of the clutch to the drive plates etc. thus toasting the clutch and saving the drive line from shock.

So if the CDV is gone/replaced is this going to happen?

[willhollin]

Originally Posted by TMP

So if the CDV is gone/replaced is this going to happen?

I guess only if you were doing clutch dumps from every standing start.

[FieldingMellish]

Originally Posted by TMP

So if the CDV is gone/replaced is this going to happen?

Toasting the clutch was caused by the CDV.

I found that I was letting my clutch up far too slowly, revving too much, and getting nowhere fast. The lack of a discernable 'bite point' and the jerkiness of the CDV progressively letting fluid flow out and the clutch operate gradually, totally robbed me of my confidence in completing fast gear changes. Prime example: pulling out at a junction, my left foot would stay down on teh clutch while my right foot bore down on the accelerator, and getting no feedback from the clutch, it became impossible to judge when to transfer from the clutch to the accelerator. With less hasty changes, I got this jerking effect where it felt as though I was being pulled forward then back then forawrd....

Naturally, the technicians at teh BMW dealer had no idea what I was talking about. I asked, "Is there some sort of 'lock valve' or 'delay valve' on the clutch which could be causing this?" to which they replied, "Um, I don't know...there's a flywheel"!

[FieldingMellish]

Originally Posted by G33

Mines better but i wudnt say a complete night and day transformation! clutch is lighter tho SSK next i think that will improve shift times no end i hope!

Well, if it's not a 'night and day' transformation, then I would say it's at least a 'twilight and high noon' one!

Don't get me wrong, it's not like there is suddenly a massively hard bite point. It's more a case of there having been no discernable bite point at all, and now there is a subtle yet palpable one.

But what really hit me was the knock-on effects, some of which are doubtless psychological some not. As noted, the clutch is now lighter which is great. But I am finding that everything now seems lighter, not just the clutch but the other pedals as well. And my gearbox suddenly feels less notchy also. Can this really be? Probably not, but with the jerkiness of gear changes gone, and the problem of the hugely stiff clutch alleviated, the notchiness of second gear seems so much less a problem.

Hoestly, I am surprised that this CDV business is not much more well-known. For my money, it should be up there with replacing the run-flat tires.

[dxb335d]

Originally Posted by FieldingMellish

How is your clutch, Carlos?

I think its fine mate

Originally Posted by R4R

Carlos it to make sure that if somebody decided to wind the engine up to 6K and dump the clutch the fluid running back from the slave cylinder to the master cylinder is restricted.

this causes a progressive application of the clutch to the drive plates etc. thus toasting the clutch and saving the drive line from shock.

there hope that helps.....

Dario

thanks

[- Paul -]

I don't understand this. My clutch bites at the same point all the time - mine must have the cdv so what's the difference?

[G33]

They all have the CDV.

The modified CDV basically has a larger diameter hole so the fluid gets in and out quicker. The one u have on your car now has a hole similar in size to a pin hole!!! to give u a rough idea

[FieldingMellish]

Originally Posted by G33

They all have the CDV.

The modified CDV basically has a larger diameter hole so the fluid gets in and out quicker. The one u have on your car now has a hole similar in size to a pin hole!!! to give u a rough idea

The hole in the new E90 CDV, as in my car, is even smaller than that. It literally is a pinhole. So maybe the CDV factor is worse in the post-Sept 2007, ED-engined cars?

[NFS]

Originally Posted by - Paul -

I don't understand this. My clutch bites at the same point all the time - mine must have the cdv so what's the difference?

With the CDV, the very last bit of movement as the clutch plates bind together is fractionally slowed. So even if you just sidestep off the pedal, the clutch plates come together gently.

It doesn't bother me in the slightest, but it does mean that you can't feel the exact point of the 'bite' when you are changing gear.

As Mr Mellish just said, I do wonder if the CDV has been changed for more recent cars, because I have no problem with this at all.

[G33]

Originally Posted by FieldingMellish

The hole in the new E90 CDV, as in my car, is even smaller than that. It literally is a pinhole. So maybe the CDV factor is worse in the post-Sept 2007, ED-engined cars?

that image was a quick one i just found for a Z4M i think. but u r right it is like a pin hole, we will have to see if it correllates to post Sept. 07 cars tho. FYI mine is so if sum posts a pic of one made before sept 07 that wud be instersting to see.

i still have my original one in the garage and wil get a pic. once i modified another stock CDV i bought it looked similar in size to the one on the right

[FieldingMellish]

The more I drive with the replacement CDV, the more benefit I see. I almost worry that it's too good to be true! I used to have to wrestle with my car, and when I was in traffic, jerking along, my left leg aching as I pumped a clutch that would not be out of place on a WWII tank, the word that kept percolating through my brain, in respect of a potential next car purchase, was 'automatic'. But now I can enjoy the pleasure of a manual again.

So, NFS, do you really never get a jerky effect, even when trying to shift quickly up thorugh 1st/2nd/3rd? Maybe you have just got used to the delayed action of the clutch? Almost certainly you are a more experienced driver than me, but I could not have lived with that jerky effect much longer.....

[- Paul -]

Originally Posted by FieldingMellish

The more I drive with the replacement CDV, the more benefit I see. I almost worry that it's too good to be true! I used to have to wrestle with my car, and when I was in traffic, jerking along, my left leg aching as I pumped a clutch that would not be out of place on a WWII tank, the word that kept percolating through my brain, in respect of a potential next car purchase, was 'automatic'. But now I can enjoy the pleasure of a manual again.

So, NFS, do you really never get a jerky effect, even when trying to shift quickly up thorugh 1st/2nd/3rd? Maybe you have just got used to the delayed action of the clutch? Almost certainly you are a more experienced driver than me, but I could not have lived with that jerky effect much longer.....

I'm not NFS but I don't have that issue on my 320d. Are you coming to uk7? You can try mine there if you want.

[G33]

im the same im afraid, theres not that as much change to mine as you state with yours. but yes there is improvement as it were

[FieldingMellish]

Well of course all this is subjective. And I am the first to admit that I am no expert driver. But I was getting more and more p1ssed off with this jerky low-speed gear changing problem, and then I heard about the CDV, shortly after which I had a drive in Anthony's SR3 and just loved the clutch action in that. So it wasn't long before I got over to Warrington and had the same CDV replacement done on my car. Even then, I doubted my clutch would miraculously become just like Anthony's but to all intents and purposes it has. My clutch *pedal* is still stiffer than the SR3's - which is counter-intuitive given that he has some sort of racing clutch installed which you might actually expect to be stiffer than stock - but it's not as stiff as it was. And the difference in smoothness of gear changes is phenomenal. This has had more effect on my car than a remap, yeah mad I know but that's how I feel. I could never enjoy my car at lower speeds because I was dreading gear changes and hated that jerky effect.

But if you don't know what I'm talking about, hey, why change? If you do experience the same problems I was having, do yourself a favour and get rid of that CDV.