[wellvrsd]

I picked up my 2017 M2 last Monday, and I am in absolute love with the car, but I've found a few things need improving regarding the clutch. At first, I thought I was just adapting to a new car, but after a while, I realized that the clutch engagement point seemed to be in different places depending on the aggressiveness of my shifting. Creeping around a parking lot, engagement was ~1/3 of pedal travel, but under full acceleration, let the clutch out as fast as my leg will move, it didn't seem to engage until the pedal was almost all the way out.

It makes sense that a car with a CDV would behave this way. When fluid is trying to escape the slave cylinder and there is a restriction at the exit, the faster you release the pedal, the more the restriction becomes the controlling factor instead of the pedal.

So I started searching the forum, and I came across this, which led me to this f30 thread. Which led to the M2 making it onto the lift only 3 days after she arrived home:



The slave cylinder is located on the driver's side of the transmission, behind the big panel in the center of this picture:



I also unbolted the heat shield behind that panel and moved it out of the way, so that I could unbolt the top slave cylinder bolt from behind the transmission using a long extension. I tried using two shorter extensions and a universal joint, but behind the transmission was easier for me. The heat shield cannot be fully removed without dropping the exhaust some, but it will move out of the way enough with the exhaust in place.



Now I had access to the slave cylinder. I removed the retaining clips at each end of the hard line, and removed the hard line. I wrapped a towel around the soft line and tucked it up into the underbody to minimize leakage. (I didn't want to clamp the line as it likely has a wire braid layer to it that could be crimped)



At this point, I attempted to get the CDV out of the slave cylinder, but found that I was not able to due to how close it was to the trans tunnel. I unbolted the two 13mm bolts holding it on and removed it. Now I could see the CDV. The f30 guys start drilling at this point, but I wanted to avoid that. I found that with the right pick, the rubber spacer and the CDV came right out. It just had to be the right pick. The two on the left wouldn't move anything, but the pick on the right pulled them both out with no trouble at all. You can see the spacer and CDV that were removed above the picks:



Here's a comparison of the size of the CDV and the hard line:



After looking things over, I suspected that the sealing surface of the joint was the ridge that I'm pointing to with the pick. I left the spacer and the CDV out, and I have not had any leaks.



At this point, I started to have brake fluid on my hands a lot, so that is the last picture I remembered to take. Installation is the reverse of removal, with a few key points. I put a dab of grease on the tip of the slave cylinder plunger as discussed in the f30 thread. The slave cylinder bolts had some blue threads when I took them out, so I reinstalled them with blue loctite. The connections on each end of the hard line are different, pulling the clip off was sufficient on each end for removal, but not for reinstallation. For the connection from the hard line to the slave cylinder, push the hard line into the slave cylinder, then slide the clip into place. To connect the soft line into the hard line, push the clip into place on the hard line, then push the soft line into the connection until the clip snaps into place. Both of these connections will have a mm or so of play in and out, that is ok. The retaining clips are smaller than the channels they reside in, that is where the play comes from.

I used the reverse bleeding method described by the f30 thread. I used this syringe that I already had in my possession, as well as some small tubing to connect the syringe to the bleeder. I didn't want to overflow my reservoir and get brake fluid on painted surfaces (brake fluid eats paint) so I filled ~50ml at a time 3 times. Since I had already removed enough fluid to lower level to the glue joint of the reservoir, I now know I could have done it all at once. The slave cylinder and the bleeder screw are plastic and unlike every other bleeder screw I've ever operated. The bleeder screw had to be open 3-4 turns, and I was still pushing the fluid in quite slowly, probably 1mL/second. To close the screw, just hold your finger over the opening to minimize leakage while wrenching. It was an 11mm, and I was happy to have a ratcheting box end wrench for this screw.

The whole job took me just over two hours, but I had to learn some things as I went, and had some distractions. I believe that if I were to do it again tomorrow, I could do it in about an hour.

I could immediately feel the difference when I drove the car. The clutch engagement occurred with the pedal lower and closed to the same point when creeping and driving. I haven't done a shift under hard acceleration yet, but will report back when I do.

Lastly, I may be afu on how I'm doing these pictures, so I'll edit them if I need to. This is my first time owning a car early enough in its lifecycle that I'm the one writing DIYs.

Edit: I was hoping the pictures would be thumbnail sized in the attachments section, not full size and doubled up. Is there a way to do this? Or if I delete them from the attachments, will they still exist on the server to display in the thread?

[M Fifty]

The big pictures are good, and repetition on DIYs doesn't hurt.

[wellvrsd]

I just got back from a drive where I was really concentrating on the clutch pedal position when the clutch engaged, and varying my rpm shift points, as well as how fast I cycled the pedal, and there is now no doubt in my mind that this was a great mod for me. The clutch is engaging at the same point in pedal travel every time regardless of how I'm driving the car or cycling the clutch. Now muscle memory can get to know the spot, helping me to make better shifts.

If you are wondering if you should do this, you need to ask yourself one or two questions. First, is something about shifting bothering you? If not, don't fix what isn't broken. If something is, go do the test I talked about above. Concentrate on pedal position at engagement. Vary your shift points and speed of pedal actuation. Do lots of 1-2 shifts. If you come out of this test feeling like your pedal position at clutch engagement is moving around, I believe you will be very happy doing this mod.

Last thing if you're still on the fence, this mod is easily reversible. You don't have to irreversibly change anything, you're just going in and removing the CDV and the rubber spacer. If you take them out and don't like the way the car drives, put them back in. And the job should go way faster the second time now that you've learned all the tricks.

[CTSean]

Well crap, and here I was thinking these cars didn't have a CDV and the weird clutch engagement was due to the upshift rev matching.

[OG Shark]

This + CAE shifter = so much more enjoyable to drive than stock

[nismoman]

I Knew it! thank your sir for finding this turd valve

[Ultimateone]

This is wild because after driving STI's and my last Focus RS I thought I was going crazy with how the clutch worked.

[eeyang92]

Originally Posted by CTSean

Well crap, and here I was thinking these cars didn't have a CDV and the weird clutch engagement was due to the upshift rev matching.

Same, I had heard BMW removed the CDV on M cars since at least the F gen.

That being said, I've never felt that it was restricted under heavy driving. For example, on the track I can slam it from 2nd to 3rd as fast as I can and I don't notice the clutch momentarily slipping (there may be some slight hesitation, but I imagine that's more ECU programming).

I do remember when I first got the car, it did seem like the bite point moved around when I was trying to drive smoothly. I think for the most part I've gotten used to the way the clutch works so it's better now, but 1-2 shift is still the hardest.

[digimattic]

Originally Posted by eeyang92

Same, I had heard BMW removed the CDV on M cars since at least the F gen.

That being said, I've never felt that it was restricted under heavy driving. For example, on the track I can slam it from 2nd to 3rd as fast as I can and I don't notice the clutch momentarily slipping (there may be some slight hesitation, but I imagine that's more ECU programming).

I do remember when I first got the car, it did seem like the bite point moved around when I was trying to drive smoothly. I think for the most part I've gotten used to the way the clutch works so it's better now, but 1-2 shift is still the hardest.

I'm the same. 1-2 when driving at anything less than full throttle always seems rough. However, I've noticed that there seems to be a LOT of rev hang which I attributed the jerkiness to. I found that, if I'm not pushing the car hard, I can slow down my shifts and the smoothness is much improved.

Can someone explain the point of this valve anyway?

[chmura]

Thanks awesome man thanks for posting! We need more DIY's like this for the M2!

I have an M2c and I believe if I'm not mistaking has the same manual transmission as the OG M2?? Will this work on the M2c?

I definitely do not like the clutch engagement feel on my M2c. Very hard to feel when the clutch engages. And I get a dip in the RPM from 1-2 shifts at WOT.

[CTSean]

Originally Posted by chmura

Thanks awesome man thanks for posting! We need more DIY's like this for the M2!

I have an M2c and I believe if I'm not mistaking has the same manual transmission as the OG M2?? Will this work on the M2c?

I definitely do not like the clutch engagement feel on my M2c. Very hard to feel when the clutch engages. And I get a dip in the RPM from 1-2 shifts at WOT.

If I understand the steps above correctly, the CDV is located in the slave cylinder itself and the slave cylinder for M2 and 2C (as well as all 1, 2, 3 and 4 M and non-M cars as far as Realoem.com is concerned) are all the same part #. It's reasonable to assume they all have the same restrictor.

[chmura]

Originally Posted by CTSean

If I understand the steps above correctly, the CDV is located in the slave cylinder itself and the slave cylinder for M2 and 2C (as well as all 1, 2, 3 and 4 M and non-M cars as far as Realoem.com is concerned) are all the same part #. It's reasonable to assume they all have the same restrictor.

Yes that is correct the CDV valve is inside the slave cylinder.

So why has this not been discovered earlier? The manual M3 and M4 has been out for 5 years now. I have not seen anything on the M3/M4 boards. Is it because the M3/M4 owners are not true enthusiasts? Really strange that on the M4 forums there no mention that the M4 has the CDV since the M2 has the same transmission as the M3/M4.

[CTSean]

Originally Posted by chmura

Yes that is correct the CDV valve is inside the slave cylinder.

So why has this not been discovered earlier? The manual M3 and M4 has been out for 5 years now. I have not seen anything on the M3/M4 boards. Is it because the M3/M4 owners are not true enthusiasts? Really strange that on the M4 forums there no mention that the M4 has the CDV since the M2 has the same transmission as the M3/M4.

I looks to have been discovered, maybe just not common knowledge and maybe not as "critical" of a mod compared to E36/46 days (I still have both of those CDVs somewhere)

https://f30.bimmerpost.com/forums/sh....php?t=1486773

[chmura]

Originally Posted by CTSean

I looks to have been discovered, maybe just not common knowledge and maybe not as "critical" of a mod compared to E36/46 days (I still have both of those CDVs somewhere)

https://f30.bimmerpost.com/forums/sh....php?t=1486773

Yes I saw that thread back 1 year ago before I got my M2c and even posted a thread about it few months ago.

I mean for the M3/M4 forums I do not see anything regarding a CDV.

[PackPride85]

Originally Posted by chmura

Yes I saw that thread back 1 year ago before I got my M2c and even posted a thread about it few months ago.

I mean for the M3/M4 forums I do not see anything regarding a CDV.

It's in all the fx cars that use the same slave cylinder....which includes the m3/m4.

[wellvrsd]

Originally Posted by chmura

I mean for the M3/M4 forums I do not see anything regarding a CDV.

When I was researching this, I did see a thread on it in the M3/M4 forum where a bunch of people pile on and tell someone that there is no CDV, and the OP doesn't know how to drive a manual.

Edit: Found the thread. My above take away may be a slight exaggeration.

[David.m]

Originally Posted by digimattic

I'm the same. 1-2 when driving at anything less than full throttle always seems rough. However, I've noticed that there seems to be a LOT of rev hang which I attributed the jerkiness to. I found that, if I'm not pushing the car hard, I can slow down my shifts and the smoothness is much improved.

Can someone explain the point of this valve anyway?

I also get the 'rev hang' driving in Comfort (I stay in Comfort till engine oil gets up to 75C or so). In Comfort the rev match is also slow, doing quick shifts in Comfort is anything but smooth for me whereas in Sport+ I find the quicker the better.

[widetyres]

Originally Posted by chmura

Yes that is correct the CDV valve is inside the slave cylinder.

So why has this not been discovered earlier? The manual M3 and M4 has been out for 5 years now. I have not seen anything on the M3/M4 boards. Is it because the M3/M4 owners are not true enthusiasts? Really strange that on the M4 forums there no mention that the M4 has the CDV since the M2 has the same transmission as the M3/M4.

Taking the UK market as an example, they only sold a very low percentage of manuals for the f80/f82.

Before buying my m2 I was tracking manual f80/82 car sales and they were probably <2% of the cars on the market. Probably why it wasnt discovered - just too few people affected.

[Nezil]

I removed my CDV last night. Getting the slave cylinder off and removing the CDV was easy, but I ended up not going to work today because I was unable to bleed the clutch system!

I'm going to post my experience in another thread, because I think it would be valuable to the community to understand the issues surrounding clutch bleeding, and the root cause of the bleeding issues. There is much mis-information out it being essential to reverse bleed, but once you understand the root cause of the issues several ways to bleed become apparent.

As for the improvement without the CDV... I've only driven the car twice, but I'm already going to say that the improvement is MASSIVE!

Every car I've had since I started driving 24 years ago, has been a manual, with the exception of my previous car that I had for 4 years. I'm pretty familiar with manual gearboxes then, but I was never really satisfied with the gearbox in the M2, but couldn't put my finger on why... Now, having removed the CDV, I can say that it was 100% the reason why, but I'll dive into the actual differences a little deeper for anyone on the fence.

With the CDV in place, the pedal position and time at which the clutch engages is unpredictable. With time and experience, you can try and learn the behaviour, but I still found that I'd get jerky shifts sometimes, particularly in slow moving traffic where you're either stopping and starting, or shifting back and forth between 1st and second at low speeds. I also felt that pulling away it was difficult to modulate the clutch as I'd like to. It wasn't jerky, but difficult to do quickly and smoothly.

Everything I've said so far was with auto-rev match enabled... with it disabled, things were far worse! The CDV effectively delays the engagement of the clutch, and if you rev-match manually, you have to make sure to rev higher than you really need, because the clutch isn't going to bite when you lift off the pedal, because it's delayed.

If you choose not to rev match, things get awful fast. The delay caused by the CDV lets the revs drop far too much as you downshift, and even if you try to slowly let the clutch bite in, that doesn't happen smoothly.

Before I removed the CDV, I'd assumed that these behaviours were due to the tune of the engine, or an overly aggressive sports engine / flywheel / clutch combination, but I now know that's not the case.

One last point... I've heard from non-M owners that the CDV causes the clutch to slip between shifts. I never found this to be the case with my M2; the shifts were delayed and sometimes not smooth, but there wasn't any slippage. This leads me to think that the M-series clutch / flywheel / CDV combination might have different issue characteristics for M owners than non-M owners. It's probably worth doing for both M and non-M, but if you're getting slipping with the CDV, my comments above may not apply.

[Nezil]

Clutch bleeding experience, root cause of issues experienced by many and solutions in this thread: https://f87.bimmerpost.com/forums/sh...php?p=25174427

[NTD619]

Hi everyone,

I completed this mod successfully without removing the clutch cylinder by using a 4-inch deck screw in the inlet. I turned the screw by hand approximately 4-5 turns once it grabbed, and pulled it out with the grommet and metal restrictor attached to the screw. No leaks once reassembled.

The syringe procedure worked for me but the clutch pedal required about 40-50 pumps to regain pressure.

Thanks for all of the guidance.

[jkoral]

Originally Posted by digimattic

Can someone explain the point of this valve anyway?

From https://www.zeckhausen.com/catalog/index.php?cPath=6562

"Due to this factory device, the clutch engages the flywheel slowly, regardless of how quickly you lift off the clutch pedal. In theory, it reduces driveline shock, if an inexperienced driver dumps the clutch. In practice, it prematurely wears the clutch disc and transforms experienced drivers into novices, who cannot shift smoothly."

(I did this on my E46s and E82 and plan to do the same for my new to me OG M2).