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?