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      05-14-2018, 12:32 PM   #1
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Any 6MT owners going to mod their clutch slave cylinder to remove the CDV?

It looks no one has seen this yet. The 3/4 series crowd has found the clutch delay valve (CDV) in the clutch slave cylinder and they have started modifying it. Basically they're just drilling out the CDV orifice to improve flow/reduce the delay. Looks simple. I'm probably going to buy a new slave ($70) and modify it.


http://f30.bimmerpost.com/forums/sho....php?t=1486773
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      05-14-2018, 01:48 PM   #2
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Interested on the outcome, might be a worthwhile mod. I can say without a doubt, though, that the diff bushings have made a significant improvement to the MT clutch engagement and disengagement. I don't have any gripes about how the clutch releases, anymore. I feel like the drivetrain movement was most of the "lag" that I was feeling before. Could be a placebo since I feel a lot more of everything, now, but if this turns out to work, for the price I might as well try it, too.
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      05-14-2018, 02:15 PM   #3
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I thought I read somewhere that the m235i doesn't have a CDV? If it does, I be really interested to know what it does.

Ken
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      05-14-2018, 05:10 PM   #4
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Quote:
Originally Posted by Dylan86 View Post
Interested on the outcome, might be a worthwhile mod. I can say without a doubt, though, that the diff bushings have made a significant improvement to the MT clutch engagement and disengagement. I don't have any gripes about how the clutch releases, anymore. I feel like the drivetrain movement was most of the "lag" that I was feeling before. Could be a placebo since I feel a lot more of everything, now, but if this turns out to work, for the price I might as well try it, too.
Which diff bushIngs did you do?
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      05-15-2018, 01:23 PM   #5
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Which diff bushIngs did you do?
Derlin
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      05-15-2018, 03:10 PM   #6
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Quote:
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Quote:
Originally Posted by SteveInfante View Post
Which diff bushIngs did you do?
Derlin
Thanks.
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      08-12-2018, 02:13 PM   #7
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Sorry to revive an old thread, but I did the mod yesterday. Getting air out of the line gave me the most issues even with reverse filling and vacuuming from the top.

The results however are well worth it, makes this gear box much more enjoyable especially in the lower gears.

For some reason I thought the brake system was separate from the clutch and just shared the same reservoir, but somehow I got air in the brake line so the pedal felt lousy for a bit then came back. Im a bit confused by this.
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      08-12-2018, 05:57 PM   #8
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Quote:
Originally Posted by ko113 View Post
Sorry to revive an old thread, but I did the mod yesterday. Getting air out of the line gave me the most issues even with reverse filling and vacuuming from the top.

The results however are well worth it, makes this gear box much more enjoyable especially in the lower gears.

For some reason I thought the brake system was separate from the clutch and just shared the same reservoir, but somehow I got air in the brake line so the pedal felt lousy for a bit then came back. Im a bit confused by this.
Nice! I'm probably going to do this once my Ultimate Clutch Pedal arrives. I'm pretty sure that thing is made out of Unobtainium because I ordered it back in June and the delivery date keeps getting pushed back.
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      08-12-2018, 08:04 PM   #9
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how am I just finding out about this now?

also, location and removal sounds like a PITA. not looking forward to this.
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      08-14-2018, 04:00 AM   #10
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Yes please! More details would be great!
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      08-18-2018, 05:58 PM   #11
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just did this today! very exited that the car still works.

write up and some pics to follow!
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      01-26-2019, 08:07 AM   #12
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Quote:
Originally Posted by delvec03 View Post
just did this today! very exited that the car still works.

write up and some pics to follow!
Did you find altering the CDV was a worthwhile mod? Did it hold up in all driving conditions? Seriously considering it myself!

Thanks.
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      01-26-2019, 08:25 AM   #13
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I did the CDV mod in both of my Z3's. It certainly made a positive difference. The CDV valve is just a restriction and doing the mod just means drilling the hole bigger, or replacing the valve with a length of "not restricted" tube. In my case I ordered a modified DCV (drilled) and swapped it with the original. The user control of the clutch engagement is much enhanced for fast shifting. If you're shifting slowly there's no particular effect. The purpose of the CDV to just to protect the system from someone who is shifting "too fast" and not coordinating the clutch/throttle properly by enforcing "slow" due to the restricted opening. In other words, avoiding warranty repairs from inexperienced manual transmission users by not letting them hurt the tranny at the expense of reduced control for those who DO know how to shift.
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      01-27-2019, 08:55 PM   #14
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Quote:
Originally Posted by M235ForNow View Post
I did the CDV mod in both of my Z3's. It certainly made a positive difference. The CDV valve is just a restriction and doing the mod just means drilling the hole bigger, or replacing the valve with a length of "not restricted" tube. In my case I ordered a modified DCV (drilled) and swapped it with the original. The user control of the clutch engagement is much enhanced for fast shifting. If you're shifting slowly there's no particular effect. The purpose of the CDV to just to protect the system from someone who is shifting "too fast" and not coordinating the clutch/throttle properly by enforcing "slow" due to the restricted opening. In other words, avoiding warranty repairs from inexperienced manual transmission users by not letting them hurt the tranny at the expense of reduced control for those who DO know how to shift.
Where did you get the modified DCV?
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      01-27-2019, 09:28 PM   #15
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Quote:
Originally Posted by VPB74 View Post
Where did you get the modified DCV?
I can't believe it, but I remembered the name: https://www.zeckhausen.com/catalog/index.php?cPath=6562
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      01-27-2019, 10:24 PM   #16
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Quote:
Originally Posted by M235ForNow View Post
I can't believe it, but I remembered the name: https://www.zeckhausen.com/catalog/index.php?cPath=6562
There is no separate CDV on the F22 or other current cars using the same clutch slave cylinder (340i, 440i, M2, M3, M4, etc). It is actually a restriction plate that is inside the slave cylinder that can be removed, according to a post on another forum, which can be found by googling ‘340i CDV remonster’
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      01-28-2019, 06:27 AM   #17
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Quote:
Originally Posted by aerobod View Post
It is actually a restriction plate that is inside the slave cylinder that can be removed, according to a post on another forum, which can be found by googling ‘340i CDV remonster’
Following that search result led to this detailed description of the procedure involved in modifying the delay built into the clutch slave cylinder, including different ways to get all of the air out after you're finished: https://f30.bimmerpost.com/forums/sh....php?t=1486773.
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      01-31-2019, 07:42 AM   #18
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Quote:
Originally Posted by M235ForNow View Post
I did the CDV mod in both of my Z3's. It certainly made a positive difference. The CDV valve is just a restriction and doing the mod just means drilling the hole bigger, or replacing the valve with a length of "not restricted" tube. In my case I ordered a modified DCV (drilled) and swapped it with the original. The user control of the clutch engagement is much enhanced for fast shifting. If you're shifting slowly there's no particular effect. The purpose of the CDV to just to protect the system from someone who is shifting "too fast" and not coordinating the clutch/throttle properly by enforcing "slow" due to the restricted opening. In other words, avoiding warranty repairs from inexperienced manual transmission users by not letting them hurt the tranny at the expense of reduced control for those who DO know how to shift.
Good feedback, thanks.

Many improvements were mentioned in the forums doing the CDV delete. I like all of them. Just wonder how many make a noticeable difference. If it is only affecting fast shifting it wouldn't be so interesting to me.

Quotes from the f30 thread:
- You can feel a difference in driving immediately, i used to hate the 1st to 2nd shift, but it transitions so smoothly now.
- Clutch pedel feels less resistance towards the end of its travel.
- Grabs harder and downshifts are more precise too.
- Understand that the CDV delays clutch engagement by limited the flow of fluid. Without it you now have complete control of the clutch.
- Thank you! For figuring this out. Made an account just to say so. The clutch was just about my only gripe with my f32. Now it is worlds better. The car will lug around in low gears and when on the highway will over take quicker. First gear takes off like a Normal car without the hesitation of the clutch delay.To those debating the outcomes. If you intended to drive the car with any type of gusto(like you should be) then do it. Don't let this pedal instill bad habits. Downshifts are now possible and she kicks out better than ever.
- Hell yea! Glad you did the mod. I love my car a lot better now. It also makes for a much easier driving experience.
- This really is different .. downshifts in particular have been amazing, every time. Can't even feel it. This is a nice gearbox all of a sudden.
- Along with a perfectly responsive clutch pedal and no more unnecessary slippage, you get a lot more feedback through the clutch pedal. I also have the clutch pedal return spring removed from my car so the pedal is very firm and I can feel everything that's going on. I think I finally understand why the CDV is there, it does improve smoothness by filtering out some of what the fluid could be telling you through your foot but I am much, much happier this way. If you like your clutch pedal to be as soft and smooth as possible, you'll probably be happier with the CDV left alone.
- For sure the best thing I've done to the car. I notice the downshifts are super quick and smooth, less noticeable change on the upshifts for me, but for sure improved.

Not positive:
- Ok, I only asked because people talked about it being a must mod on the e46 m3 and I did it on mine after about a year of driving it with the cdv in tact and noticed like no difference whatsoever.
I think sometimes with this stuff people sort of hype it up like it is something super noticeable when it really isn't and just get the ol placebo effect.
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      01-31-2019, 10:02 AM   #19
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With the F22 the CDV isn't very aggressive, I haven't had the clutch pedal not follow my foot in a fast shift yet (although I don't depress the clutch all the way down in most shifts, just enough for the gear lever to move easily through the gate).

On our 2016 Golf R the CDV was much more aggressive than on any of the BMWs I have owned (removed the CDV on E46 and E85). With a fast shift on the Golf the pedal would lag and come up and hit my foot on release, accompanied by the smell of burning clutch if I fed in throttle too fast. Here is a picture of how small the approximately 1mm diameter orifice was before I removed the restrictor plate on that car:
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      04-07-2019, 09:45 PM   #20
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Hi, I'm one of the people who modified the CDV referred to in the F30 thread linked above (2016 340xi). I actually went back in later and completely removed the restrictor and rubber bushing inside the slave cylinder. I should have done it from the get go. The restrictor is not needed and even if you enlarge the hole in it, there's still material in the way of the fluid. There was an even better clutch response after I removed the parts. That's the way to go.
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      06-16-2019, 07:44 PM   #21
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Hi all, I just did a write-up on removing the CDV from my M2:
https://f87.bimmerpost.com/forums/sh....php?t=1625114

This was one of the threads I referenced before diving in, so hopefully I'm returning the favor for someone.

Last edited by wellvrsd; 06-16-2019 at 07:55 PM.. Reason: Better Link
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      08-06-2022, 05:17 PM   #22
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Just throwing this in all the threads for reference. This is out of my F22 228 6MT

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