# Clutch Delay Valve (CDV) Information



## Karl (Dec 23, 2001)

Cross-posted to forum.e46fanatics.com and e46.dtmpower.net:

This is supposed to be a summation of all knowledge to date on the Clutch Delay Valve (CDV), also known as the Clutch Check Valve. A lot of research to date has been done by Nick325xiT5spd, The HACK, and tim330i, which is summarized in this post on the Bimmerfest forums, as well as this thread and this one.

I followed Nick325xiT5pd's quickie instructions for removing the CDV from my 2001 330xi (late January build), and in the end it all worked out. Here are some tips (read Nick325xiT5spd's info first):

1. Remove the CDV only if you are intending to flush your brake and clutch fluid as well, otherwise, if you don't know what you're doing, you could empty the clutch hydraulic line without much in the reservoir to fill it back up.

2. Use a very large towel or an oil drain pan to catch the hydraulic fluid that will inevitably pour out upon screwing open the clutch line. Be careful not to get any in your eyes.

3. The two ends of the line on either side of the CDV screw together perfectly, there is no hurt in removing the CDV and leaving it out - no fluid will be leaked, and everything fits like a glove.

4. The CDV on the E46's does not look like the one in the UUC tech tips page. There are photos at the bottom of this post that show the E46 valve.

5. Have someone help you manually bleed the clutch line. Pressure bleeders may not work so well if there is air in the clutch hydraulic line. It takes about 40-50 pedal pumps to completely cycle the fluid in the clutch line.

That being said, a big thanks to topazmania for helping me out with the CDV removal and brake/clutch fluid flush.

Now to the exciting part... the review. Both topazmania and I drove my car before, and after the removal. I seemed to notice a lot more difference in the way the clutch responded, perhaps because I am still not used to having the CDV installed. Topazmania, on the other hand, has tracked his car several times and has much more experience with a manual transmission than I do, and although he noticed a difference, it wasn't as pronounced, in his opinion. Maybe I was just giddy. The car is now much easier to get rolling from a standstill, and the clutch behaves exactly as the pedal behaves. That is to say, if you have the pedal at a certain position, the clutch is also at that position. It no longer "hesitates", nor will it unexpectedly engage during slow starts. It feels a lot more like other manual transmission cars I've driven. Worth the removal effort? Most definitely.

We bled topazmania's clutch and brakes as well, and checked his clutch line for the existence of a CDV... lo and behold, there it was, right where it should be on an E46. We didn't remove it just yet (he wanted to experiment on my car first), but the interesting part is that he has a 2001 325i, yes, the RWD model. Perhaps that will throw a wrench into the gears that are trying to find a pattern in CDV occurrences.

So I took a few pictures of the little bugger. It's 3.55cm long, 1.35cm outer diameter and 1.00cm inner diameter on the smooth side, 1.00cm outer diameter and 0.40cm inner diameter on the threaded side. The hex flange is a 17mm. The best estimate I can make on the diameter of the inner hole is <1mm. Along the edge of the smooth side is written "BMW 6 755 892" along with "1.7" next to the symbol for diameter. There is also a third symbol which I can't identify next to the letter "K". In the head-on photos, you can see the size of the actual hole - it's tiny.


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## Nick325xiT 5spd (Dec 24, 2001)

Excellent writeup!

Glad you're pleased. (Also glad, nothing broke. )


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## paul330ci (Apr 26, 2002)

Better find out which cars have a CDV before another CDV fire storm brews up.

My '01 330ci doesn't have one and neither does my brothers '01 330i.


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## Nick325xiT 5spd (Dec 24, 2001)

Thus far, indications are that you can assume all xis have it, but beyond that... :dunno:


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## Rmart (Feb 20, 2002)

*Why does BMW install the valve?*

Thanks


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## The HACK (Dec 19, 2001)

paul330ci said:


> *Better find out which cars have a CDV before another CDV fire storm brews up.
> 
> My '01 330ci doesn't have one and neither does my brothers '01 330i. *


For the E46, all Xi's have it. Everything else does not. Don't know about M3s, if someone has a stickshift M3 in the Los Angeles area willing to let me crawl underneath the car to find out, I will do the work.

Supposedly pre 09/99 E46es have it. Again, I have not seen any pre 09/99 car so I can not speak for this personally.


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## ride365 (Dec 19, 2001)

is it me, or do these 3 statements all contradict each other?



Karl said:


> *checked his clutch line for the existence of a CDV... lo and behold, there it was... but the interesting part is that he has a 2001 325i, yes, the RWD model. *





The HACK said:


> *For the E46, all Xi's have it. Everything else does not. *





The HACK said:


> *Supposedly pre 09/99 E46es have it. *


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## ride365 (Dec 19, 2001)

Rmart said:


> *Why does BMW install the valve?*


supposedly to make it easier for novices to shift and to smooth out sloppy clutching [sort of like the delayed throttle response], but i think it just makes it worse for more experienced people [sort of like the delayed throttle response].


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## bmw325 (Dec 19, 2001)

*Re: Re: Clutch Delay Valve (CDV) Information*

Yes, they do. And that's why this CDV thing remains so confusing. I have a 2001 325i, and find the clutch to be very iriitating-- so I'd like to believe that I have one and that it is the source of all my problems--since it sounds like its fairly easy to remove. Despite all of the contradictory statements, we now have enough info to atleast find out (by crawling underneath our cars and unbolting the transmission pan) is we have this part. I think there's enough reasonable doubt to discount an blanket statements about which cars have or do not have the cdv.



ride365 said:


> *is it me, or do these 3 statements all contradict each other?
> 
> *


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