Bleeding the Z3M clutch slave

[Z3MROADY]

I guess I am extremely fortunate. Mine bleeds all by itself. I just have to make sure the reservoir is filled and pump the pedal a dozen times and it is ready to go.

You've been able to bleed it successfully that way after changing a slave unit or hose?

[jbrannon7]

You've been able to bleed it successfully that way after changing a slave unit or hose?

The last time I had an issue was when I replaced the brake fluid using a Motive unit, maybe 6 months ago. I did all four brakes and the clutch, when I was done the brakes were good but the clutch had no pressure at all, went straight to the floor. I just pumped it until it got firm again and has been fine ever since.

[Bobkid]

The actual pushrod has nothing to do with the stroke. What you need is a smaller bore slave cylinder. It just so happens one exists. E36 325i. Stock is 7/8" bore, the 325i is 13/16", roughly 15% longer stroke.

Sorry for digging up an old thread, but found this Randy tip on a search last week, ordered the 325i slave cylinder, and now my clutch finally engages where it should again. My old one at best was barely off the floor, and now I've got room to actually use my big boy clutch stop in the floorboard again.

Didn't have the special tool to compress the slave for bleeding, but was able to rig it with a large Pittman arm puller and that gave me a real good bleed.

Thanks again to all of you who so freely share your experience on here, it is much valued and appreciated.

[Mr Bingley]

You know, by virtue of driving a different sports car recently, my attention fell on the fact that my ///M clutch engages very near the floor. I'm going to order one of Randy's 325i e36 slaves and give it a try. Thanks for dredging this back up.

[rf900rkw]

A braided steel flex line helps a lot, too. Much simpler to do both at the same time. Assemble the hose and cylinder off car. Bench bleed the assembly. Then switch out the complete assemblies. If you do it right, you will not need any further bleeding.

[Z3MROADY]

Its been just over a year now since I switched to the 325i slave (and braided hose) for my '98 M. Still going strong. Good engagement point, smooth shifts, etc. Strongly recommend it.
Edit: BTW the BMW part # for the 325i slave is 21521159045.

[Mr Bingley]

A braided steel flex line helps a lot, too. Much simpler to do both at the same time. Assemble the hose and cylinder off car. Bench bleed the assembly. Then switch out the complete assemblies. If you do it right, you will not need any further bleeding.

You know, I replaced the clutch line with a 3.0 line a year or two ago, and that did make a huge difference in engagement. I have no issues with engaging or disengaging now, jut it catches right at the floor. For comparison, I drove my other ///M Roady today, and it catches right at the floor too. Both engage and disengage just fine--no issues, but after driving my Viper, these just seem too close to the floor. Anyway I'll try a stainless braided line and the e36 325i slave, and bench bleeding and installing as you suggest--but if I end up with brake fluid running into my arm pit I'm going to curse you loudly.

[Chamberlin]

Installed a 3.0 line on my M Coupe last year too, and mine also engages near the floor...totally different than my stock M Roadster.

[rf900rkw]

Oh, you will definitely have brake fluid dripping off your elbows. That's the price you pay for not letting the system drain. There is a trick to minimize it.

[Mr Bingley]

Oh, you will definitely have brake fluid dripping off your elbows. That's the price you pay for not letting the system drain. There is a trick to minimize it.

Longer arms?

The triumvirate of auto fluid curses: bake fluid running into your arm pits; hypoid gear oil running into your hair; and antifreeze drenching you at the start of an all day job.

[pine1000]

Posting this here because it relates to bleeding the slave.

I have created a 3D printable slave cylinder compression tool. You just need to supply 3 1/4" bolts to complete it.

Details are available on thingiverse here: https://www.thingiverse.com/thing:2829161


IMG_20180316_184345.jpg

[vikrampatel86]

Thanks all who contributed to this. Just changed the clutch hose on my 98 m roadster which was getting harder to get into 2nd after a 45 minute commute. Just wanted to jot down some issues/tips I came across along the way.
Tip: if you don't already have a set of crows foot wrenches for the master side hose, get a good set. Was tough getting them last minute but i got a duralast set from autozone which had too much slop where it would round edges. Especially on all these 21 year old nuts and bolts. Use randy's method with extensions to disconnect the hose on the master side. Seemed the easiest. Also let the car cool unless you want burned wrists.
I took the slave out of the bell housing to bench bleed. Came off no issues. But the 8mm threaded fitting in the slave was stuck. The edges rounded in no time, couldn't even use vice grips. I had to put the nut in a vice and spin the body (my S.S. line replaced the bit of hard tubing) - cleaned up all the threads and installed the s.s. line.
Tip #2: Clean the threads of any hose /tube connections before trying to reinstall (while they are plugged) - if needed. I took too much time trying to thread the bench bled slave with hose to the hard tubing and by the time i got the thread started, it seemed like there as no more brake fluid dripping from the hard tubing (AHHHHH AIR).
At this point i tried getting a vacuum pump, tried the air compressor vacuum bleeder (garbage) and tried the conventional method of bleeding (with a helper on the clutch pedal). The clutch went straight to the floor and had to be pulled up. After 50+ pumps of the clutch pedal by hand, still had no pressure. After a while of trying to vacuum pump out the air, I reverse bled the system. Took the slave cylinder back out, and bench bleed that again, cause after all the attempts at taking air out, i think i put more air in. Hooked up my manual vacuum pump the other direction, sucking from a bottle of brake fluid into the hard line tube from the master. Once i hooked the slave back up, i had significant pressure in the pedal.
I went back to the conventional method which worked great. about 7-10 cycles of pedal in - bleeder open - bleeder closed - pedal out. Made sure i wasn't getting any more bubbles and i was set.

I'm hoping I didn't mess anything up or now trap air in the master but the pedal is solid out right now, with no wiggle and before, the clutch engaged towards the floor, now i'm engaging much higher (makes me think there could have been air in the system before i started).

Last tip - if it's your first time, it's difficult to tell if the shaft on the slave is on the landing spot in the bell housing. Especially after you've attached the stainless line to the master side tubing. You can't tell if the spring back is from the S.S. hose or from resistance in the slave. We felt the resistance on the plunger while it was off and mimic'd that when reinstalling, trying to hold the s.s. line in a way where we can definitely tell it was resistance from the plunger and not the line. Also i had some practice since i had to bench bleed twice.

[ProductUser]

I just had the clutch slave cylinder and UUC stainless line installed last week. The improvement in the clutch pedal during city traffic was immediate.