Clutch Master and Slave Replacement Tips

[cerealwars]

Howdy!

I recently replaced my clutch master and slave cylinders. Bleeding the system proved to be an absolute bitch of a time for me, so here's some notes to make it hopefully less sucky for you.

This is not a DIY, as replacing these parts are fairly intuitive, and there's enough videos on youtube for that.


-EDIT: Adding a big ol' disclaimer that my problem turned out to be not an internal hydraulic failure of either of the cylinders, but instead - A totally shot pilot bearing. I kept starting the car after bleeding and I couldn't put it in gear, because the worn bearing was causing the crank to grab the input shaft of the trans. Seemed to me like the clutch wasn't disengaging, so I probably bled this system more times than I needed to. Oh well, there's still a ton of methods and good info for you here.


-Use clear silicone tubing! For everything!! If you can't see whether you're bleeding fluid or air, you can't really be sure what's going on.

-The slave bleeder screw is sensitive. In my case, it needed to be opened 1.25 turns before fluid really starts to flow.

-Bench bleed the crap out of both cylinders. You will get fluid everywhere. Embrace the suck. Wet rags are your friend. Put one in the pedalbox and swap the new master in while losing as little fluid as possible.

-Note that the plastic male quick-connect fittings should have a small square-cut stepped o-ring installed on the end of them. These can fall off during disassembly. Make sure there's one in between the master and the hardline, or you will dump a cylinder full of fluid onto your carpet.

-I used vice grips to keep fluid from coming out of the soft line that feeds the master while swapping cylinders.

-I used a large 200cc automotive syringe (one titled Thorstone 200cc Automotive Fluid Extractor Pump, Manual Oil Change Syringe with 2pcs 22cm PVC Suction Tubes off of Amazon) to push fluid in from the bottom. The master pushrod must be ALL THE WAY back (pedal up, if connected) in order to let fluid up and through to the reservoir.

-To finish, I used a bleeder wrench kit with silicone tubing and a one-way check valve from Amazon. Clear silicone tubing is a MUST for this job. Highly recommend these.

- The clutch partition of the reservoir is nowhere near as big as you think it is. Filling it to the very brim, I could exercise the pedal ~12 full cycles before needing to add fluid. Even though the reservoir still appears full, you WILL push air into the system not long after 12. Remove your clutch stop if you have one to maximize stroke length.

I found this video:

to be extremely helpful in getting the slave fully bled.

I found this video:

to be somewhat helpful in drawing small air bubbles upward out of the system from the top by creating a vacuum with the syringe. This was not very effective, but maybe could help if you just need that last little bit.

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Last but not least, I got some help from a friend who has been a BMW tech for several years. I should have asked him right off the rip, but he sent me this helpful diagram after I had already finished.

"Remove the slave cylinder from the trans, use a 2x4 to hold the shaft then zip-tie it so it stays fully depressed. Then, if you have any way to push fluid up through it, that's the best way. If not, just make sure the bleeder is the lowest point and gravity bleed it."

Hope this helps someone.