E30 318i: Replacing Clutch Slave-Cylinder - Quick + dirty guide!

Clutch reservoir suddenly low on fluid? Gearbox housing covered in it? Sounds like a popped slave-cylinder. Not to worry, this has to be one of the easiest to replace ever made!

* This guide covers the M40 engine and 5-speed gearbox, but process is the same for most models. *

1. Lift the left side of the car.

2. Remove the 13mm nut from the outer side of the slave-cylinder. This one is easy to access and can be got with a ring-spanner or socket, but the ratchet is quite snug to the gearbox.

3. Remove the 13mm nut from the inner side of the slave-cylinder. This is quite difficult to get to as it is inhibited by the clutch-hose as well as limited access in the trans.-tunnel. I managed it with a socket and a 4" extension bar to get past the hose/pipe. 

* I have seen someone getting that difficult to reach nut using a longer extension bar and the ratchet further back behind the gearbox, but this was not possible on my E30, so I'm guessing this may be for 4-speed boxes or older M10/M20 engines. If yours cannot be got with the details in step 3, then try this. *

4. Remove the slave-cylinder fr the gearbox and allow to hang down on the hose.

5. Clamp the hose (optional, but saves time when bleeding system later).

6. Remove the hose end from the slave-cylinder using an 11mm wrench so the old unit can be discarded. [It is much easier to grip the slave-cyl. by hand while it is removed from the gearbox and get a turn on the pipe-collar, as well as minimising leaks from the hose.]

7. Prime the new slave-cylinder by removing the bleed-nipple and carefully pouring DOT4 brake/clutch fluid into the hole at the top for the hose/pipe until the air is displaced and the fluid run out of the lower hole. It won't need much. Refit and tighten the bleed-nipple. 

8. Refit the hose-end to the slave-cylinder and remove the hose-clamp if you're using one.

9. Refit the slave-cylinder to the gearbox and tighten the two 13mm nuts.

10. Top up the clutch reservoir with DOT4 brake/clutch fluid and bleed the system of air. [Which bleeding technique you use is up to you, but for all BMW clutches I would recommend using a one-way valve attached to the bleed nipple as detailed in THIS POST, which saves time and headaches.]