Note: Before starting work, read the warning at the beginning paragraph 8 about the dangers of hydraulic fluid and a warning at the beginning paragraph 5 about the dangers of asbestos dust.
Removal
Note: New caliper pin bolts will be required for installation.
1. Place chocks under the front wheels, then jack up the rear of the vehicle and place it on stands (see "Lifting the car and placing it on supports"). Remove the corresponding rear wheel.
2. Reduce fluid loss by first removing the master cylinder reservoir cap and then covering it tightly with a piece of polyethylene to create an airtight seal. The flexible brake hose can be clamped with a suitable clamp. Do not use a vice or other device with flat jaws to avoid damaging the hoses.
[Article borrowed from the web portal: MercedesMan.ru]
3. Clean the area around the nipple, then loosen the brake hose union nut on the caliper.
4. Remove the pads as described in paragraph 5.
5. Loosen and remove the caliper mounting bolts, then unscrew the caliper from the end of the flexible hose and remove it from the vehicle (see fig. 9.5).
Fig. 9.5. Loosen and remove the caliper mounting bolts (shown by arrows)
Caution: Never loosen the bolts that hold the two halves of the caliper together. If the bolts are loosened and the caliper body is disassembled, the assembly may leak after reassembly.
6. With the support on the workbench, wipe off all traces of dust and dirt, but avoid inhaling the dust as it is harmful to health.
7. Mark each piston and the corresponding cylinder bore to avoid having to change them during assembly.
8. Remove the partially protruding pistons from the caliper body and remove the dust covers.
9. Using a small screwdriver, remove the piston hydraulic seal, being careful not to damage the cylinder bore surface.
Tip: Before you finally pull the pistons out of the cylinders, check that they all move easily. If any piston cannot be pulled out by hand, insert a wooden block into the caliper body (thickness approximately 28 mm) press out the pistons by applying compressed air to the hole in the brake hose fitting. You need a small amount of pressure, which can be created using a foot pump. Make sure that the pistons move out simultaneously until they hit the block, then remove the block from the caliper. This will prevent one of the pistons from getting stuck in the caliper, which will then be very difficult to remove.
Repair
10. Clean all parts thoroughly with ethyl or isopropyl alcohol or clean brake fluid. Never use gasoline or kerosene based solvents as they attack the rubber parts of the hydraulic system components. Dry the parts immediately with compressed air or a clean lint-free cloth. Use compressed air to blow out the fluid passages.
11. Check the condition of the parts and replace any that are worn or damaged. Check especially the cylinder bores and pistons; they need to be replaced (please note that the entire assembly is being changed) if they have scratches.
12. If the unit can be used again, purchase the appropriate repair kit from your Mercedes-Benz dealer. Of course, all rubber seals must be replaced, they cannot be reused.
13. When assembling, ensure that the parts are clean and dry. Install each piston into the corresponding hole in the caliper.
14. Take the first piston and dip it and the new piston seal into clean hydraulic fluid. Lubricate the surface of the cylinder bore with clean fluid.
15. Install the new piston seal using only your fingers (without fixture), to install the seal into the groove in the cylinder (see fig. 9.15).
Fig. 9.15. Rear brake caliper piston structure and dust seal
1 Piston
2 Piston seal
3 Dust cap
16. Install the new dust cover into the groove on the piston. Using careful rotational movements, insert the piston without tilting it into the corresponding hole in the cylinder. Press the piston all the way in and install the outer edge of the dust cover into the groove on the caliper body.
17. Repeat the described steps on the remaining pistons.
18. Before pressing the pistons into the caliper until they stop, position each one so that the protruding part will face upward when the caliper is installed on the disc. Mercedes-Benz dealers use a special device to ensure that the pistons are installed correctly (see fig. 9.18). The protruding part of the piston ensures contact of the pad with the disc at a slight angle, which reduces the likelihood of brake squeal.
Fig. 9.18. Correct piston position in the rear brake caliper
1 Support
2 Special device for installation
3 Piston
4 Disc
Installation
19. Remove all traces of old locking compound from the threaded holes of the caliper mounting bolts by going through the threads with a suitable tap.
Tip: If you don't have the required tap, go through the threads using an old bolt with a split groove on the thread.
20. Screw the caliper all the way onto the flexible hose fitting, using new sealing washers where necessary.
21. Slide the caliper assembly into place, then install the new mounting bolts and tighten them to the specified torque.
22. Tighten the brake hose nipple nut to the required torque and remove the clamp from the hose or the piece of polyethylene from the reservoir (depends on what you used).
23. Install the brake pads as described in paragraph 5 and bleed the hydraulic system as described in paragraph 2. Note that if the recommended measures have been taken to reduce fluid loss, only the relevant rear brake should be bled.
24. Install the wheel, then lower the vehicle to the ground and tighten the wheel bolts to the specified torque. Check the fluid level as described in "Weekly check". Check the brakes thoroughly before driving on the road.