Mercedes-Benz W201 rear brake bleeding and weak rear brakes
Why do the Mercedes-Benz W201 rear brakes not bleed or hold?
Common causes are a rear caliper fitted the wrong way round, a stuck piston in the caliper and a faulty master cylinder. The caliper's bleed screw must point upwards. If fluid does not reach the rear circuit even after replacing the master cylinder, check the calipers first of all.
How are the rear brakes bled when the air will not come out?
The rear circuit has its own compartment in the fluid reservoir, and the reservoir is kept almost full. The bleed screw hose can be routed into the fluid reservoir and pumped slowly until the bubbles stop. Pumping may take many strokes. Bleed both the front and rear circuits, as they are separate.
How can a stuck piston be freed?
The caliper is removed and the piston is moved back and forth with light tapping, aided by CRC oil. If the piston will not come free, it is cleaned and the surfaces are sanded, the seals are renewed or the caliper is replaced with a working one. Brakes are safety-critical, so have a workshop check the result.