# Master cylinder rebuild

Remove master cylinder

NOTE : If the master cylinder does not have the exposed stop screw on the bottom, it cannot be rebuilt.

Press piston rod in slightly and remove circlip from housing.

Remove stop screw on bottom of master cylinder and slide piston rod out slowly.

Turn master cylinder upside down and knock against a block of wood to remove the second piston and seals.

Clean any components to be re-used with alcohol and dry completely with compressed air.

Check bore of housing for any corrosion, pitting or rust. Replace if bore is not perfect.

Coat cylinder bore with ATE brake cylinder paste or equivalent.

Assemble piston and seal components in the same order they were removed and, with the cylinder held in a vice, slide the piston assemblies into the master cylinder housing.

Rebuild kits from BMW come with a guide sleeve to help guide the contents of the master cylinder into place.

Once piston assemblies are bottomed out in cylinder, insert stop screw with a new seal and tighten to 5-8 Nm (3.7 - 5.7 ft lbs.)

Release pressure from piston rod and allow it to relax, gently.

Install stop washer and secondary cup and press into master cylinder until point of resistance.

Install plastic bushing in rear of master cylinder and while pressing in piston rod, install circlip.

Install new seal on outer surface of master cylinder before installing on vacuum booster.

E30 M3 Repair Manual V2.7. Copyright ©1999-2001 Koala Motorsport & Brett Anderson