Brake master cylinder — disassembly and assembly (BMW 3 Series E21)

Disassembly

Push the piston slightly into the cylinder and unscrew the lock screw.

Remove the retaining ring and take out the front brake actuator piston.

Remove the rear brake actuator piston by lightly tapping the cylinder on a wooden block.

Disassembling the front brake actuator piston

After unscrewing the connecting screw, remove the spring plate, spring, pressure ring, outer main seal and spacer washer, and then take out the pressure ring, inner main seals, spacer washer and pressure ring.

Disassembling the rear brake drive piston

Remove the spring, pressure ring, main seal and spacer washer. Remove the spacer seals.

Assembly

Thoroughly wash all parts and the cylinder body with alcohol or fresh brake fluid and dry with a jet of compressed air. Check the technical condition of the parts.

The assembly of the master cylinder is carried out in the reverse order of disassembly, taking into account the following:

• the rear brake actuator piston spacers should be installed so that their edges are facing in the opposite direction;
• the pressure ring of the front brake actuator piston must rest against the main cuff;
• lubricate the assembly parts and the cylinder mirror with paste for brake working cylinders;
• when installing pistons, use bushing 34 3 010 to avoid damaging the seals;
• before tightening the locking screw, slightly compress the pistons;
• each time the cylinder is disassembled, replace the copper sealing ring installed in front of the front brake actuator piston retaining ring;
• lubricate the cylinder piston drive rod with silicone grease.