Replacing the rear brake caliper repair kit on a Mercedes-Benz W124 involves disassembling, cleaning, and rebuilding the brake caliper. It’s a detailed process that requires precision and care to ensure the brakes perform correctly.

Follow this structured guide to do it safely and effectively.

Tools and Materials You’ll Need:
  • Rear brake caliper repair kit
  • Brake fluid
  • Brake cleaner
  • Brake piston tool (for compressing the piston)
  • Socket set
  • Wrenches
  • Screwdrivers
  • Rubber mallet
  • Brake bleeding kit
  • Safety equipment (gloves, safety glasses)
1. Safety Precautions
  • Park the vehicle on a flat, stable surface.
  • Turn off the engine and engage the handbrake.
  • Wear safety gloves and glasses to protect yourself from brake fluid and debris.
2. Lift the Vehicle
  • Use a car jack to lift the rear of the vehicle.
  • Secure it with jack stands before working underneath.
3. Remove the Rear Wheel
  • Remove the rear wheel to access the brake caliper.
4. Check the Brake Fluid Reservoir
  • Inspect the brake fluid reservoir.
  • If full, siphon a small amount of fluid to prevent overflow when compressing the caliper piston.
5. Disassemble the Brake Caliper
  • Unbolt the brake caliper from its mounting bracket.
  • Disconnect the brake line carefully using the correct wrench or socket.
  • Catch any leaking brake fluid in a suitable container.
  • Remove the retaining bolts, pins, and hardware holding the caliper together.
6. Remove the Old Seals and Piston
  • Extract the old piston, seals, and o-rings from the caliper body.
  • Inspect all components for rust, damage, or wear.
7. Clean the Caliper
  • Use brake cleaner to thoroughly clean the caliper housing, piston bore, and all parts.
  • Ensure all dirt, debris, and old brake fluid are completely removed.
8. Install New Seals and O-Rings
  • Fit the new seals and o-rings from the repair kit into the caliper.
  • Lightly lubricate them with clean brake fluid to aid installation and prevent damage.
9. Compress the Piston
  • Use a brake piston tool to gently compress the piston back into the bore.
  • Ensure the piston sits flush with the caliper housing.
10. Reassemble the Caliper
  • Refit all bolts, brackets, and pins as per manufacturer instructions.
  • Reconnect the brake line securely.
11. Bleed the Brake System
  • Use a brake bleeding kit to remove any trapped air from the system.
  • Start with the furthest wheel from the master cylinder, then move closer.
  • Refill the reservoir as needed.
12. Refill Brake Fluid
  • Top up the brake fluid reservoir with fresh brake fluid.
  • Replace the cap securely.
13. Test the Brake Pedal
  • Pump the brake pedal several times to seat the caliper piston.
  • Check for leaks around the caliper.
14. Reinstall the Wheel and Lower the Vehicle
  • Reinstall the rear wheel and tighten the lug nuts.
  • Carefully lower the vehicle to the ground.
15. Final Brake Test
  • Test the brakes gently to ensure proper operation.
  • The brake pedal should feel firm, and the vehicle should stop smoothly.
  • Reinspect the area for any leaks or loose fittings.
Important Note

Rebuilding a rear brake caliper on a Mercedes W124 requires precision and care.
If you’re not confident in performing brake repairs, it’s best to consult a professional mechanic to ensure safety and correct operation.