Mercedes-Benz W123 brake caliper piston seized
Mercedes-Benz W123 brake caliper piston is seized: how do I remove and clean it?
1. Remove the brake pads and try to press the piston in with a clamp. 2. If the piston does not move, remove the caliper and push the piston out. 3. Clean the cylinder, if necessary with 1000-grit sandpaper. 4. Fit the piston with new seals and lubricate it with brake fluid. Brakes are safety-critical: have a workshop check the result.
What should I use to soak seized caliper parts, and what must I not use?
Lamp oil or white spirit loosens seized parts better than detergent. Petrol hardens and embrittles the seal rubbers, and it does not loosen the piston. CRC and WD-40 swell brake rubbers, so do not spray them under the piston. The right lubricant is brake rubber grease.
A rubber on the brake caliper leaks brake fluid: is replacing the rubbers enough?
It is enough if the leaking rubber is the piston seal. The dust boot does not hold pressure, so replacing it does not help a leak. The repair kit usually contains both rubbers, and they should be replaced together. Brakes are safety-critical, so a workshop should check the work.
Why does the rear brake of the W123 drag?
The rear has disc brakes, and the drums are only for the parking brake. The cause of dragging is usually a seized piston or a fault in the rear brake hose, where the hose can act as a non-return valve and the pressure cannot release. If cleaning the pistons does not help, the caliper or the seals are renewed.