Note. You will need the following special tools to perform the procedures below: Dial meter (to check disc runout); vernier caliper (for measuring the residual thickness of the disc) and steelyard (for measuring the drag force of the brakes).
1. Jack up the rear of the vehicle and place it on jack stands. Remove rear wheels.
2. Through the viewing window in the caliper body, evaluate the residual thickness of the friction linings of the brake pads (see accompanying illustration). If the lining thickness of any of the pads is less than the allowable (see tables of sizes and adjustments at the end of the guide), or if the pads are contaminated with grease or brake fluid, replace all four pads on the brakes on both wheels.
Note. If the pads are dirty, you must also find and eliminate the cause of the leaks.
3. Using a syringe, pump out approximately two-thirds of the nominal amount of brake fluid from the GTZ reservoir.
Note. The used liquid cannot be reused.
4. The liquid is removed in order to prevent it from flowing over the edge of the reservoir when the caliper pistons are sunk to replace the pads.
Attention! Do not remove all fluid from the reservoir, as this will require bleeding the hydraulic system.
5. Loosen the bottom guide pin bolt and rotate the caliper body up on the top pin (see accompanying illustration), opening access to the brake pads, shims and holders in the anchor bracket (guide pads) caliper.
6. Remember the installation position of the components and remove the holders, blocks and shims from the anchor bracket.
7. Check shims and holders for signs of wear and damage. Replace defective components.
8. Install the shims on the shoes, then install the anchor bracket in their seating positions (with gaskets) and holders. Lightly lubricate the holders with silicone grease.
9. Push the piston perpendicularly into the caliper cylinder. Use a clamp if necessary.
10. Make sure that the caliper slides freely on the guide pins, then lower it onto the blocks.
11. Install the lower guide pin and tighten its bolt to specification.
12. After completing the replacement of the pads of both brake mechanisms, depress the brake pedal several times in order to shrink the pads on the discs. If necessary, add brake fluid to the reservoir to the correct level.
13. Install the rear wheels and lower the vehicle to the ground.
14. Carry out a road test of the car, checking the proper functioning of the brakes.
Caliper overhaul
Rear Disc Brake Caliper Components
1 - bolt; 2 - support; 3 - cuff; 4 - protective cover of the guide pin; 5 - piston; 6 - guide pin; 7 - anther; 8 - anchor bracket; 9 - fixing ring; 10 - holder; 11 - protective cover of the guide pin; 12 - bolt; 13 - guide pin; 14 - shims; 15 - pads; 16 - adjusting gasket; 17 - holder
1. Jack up the rear of the vehicle and place it on jack stands. Remove rear wheels.
2. Give a union bolt and disconnect a brake hose from a support. Cap the end of the hose to prevent dirt from entering the hydraulic system and to minimize brake fluid loss.
3. Turn out a bolt of the lower directing finger, turn a support upwards and remove it from the upper directing finger.
4. Remove the piston boot retaining ring.
5. Press a block of wood against the anchors of the caliper body pads and carefully press the piston out of the caliper cylinder while applying low pressure air to the hydraulic hose fitting hole on the caliper body.
Note. Excessive air pressure can cause the piston to extrude at high speed, resulting in personal injury or piston damage.
6. Remove the boot from the piston and remove the piston cuff from the cylinder.
Note. To remove the cuff, use a blunt tool, preferably made of plastic or wood.
7. Remove the shoe components from the anchor bracket.
8. Flush the caliper cylinder and piston with clean brake fluid.
9. Check the cylinder bore for cavities, corrosion, signs of wear and damage. Replace the caliper body if necessary.
Note. Minor defects can be removed with fine sandpaper.
10. Check the piston for cavities, corrosion, signs of wear and damage. Replace if necessary.
Attention! Do not attempt to polish the piston with fine sandpaper as this will damage the piston lining.
11. Check the condition of the shoe components, guide pins and anchor bail. Replace defective parts.
12. Discard all rubber components removed from the caliper assembly.
13. Lubricate the new piston seal and boot with rubber lubricant and install the seal in the cylinder groove. Follow the correct fit of the cuff in the groove - it should not be twisted.
14. Put the boot on the piston and lubricate the latter with clean brake fluid.
15. Fully sink the piston into the caliper cylinder and secure the dust boot in the groove on the edge of the cylinder, fix it with a mounting ring.
16. Install shoe components into anchor bracket.
17. Hook the steelyard to the wheel stud and measure the resistance force. Write down the result of the measurement. If necessary, check the wheel bearing preload adjustment.
18. Using a dial gauge mounted on the front suspension component with a plunger pressed against the end surface of the brake disc, measure the amount of disc runout. If the measurement result is out of range (see tables of sizes and adjustments at the end of the guide), grind the disc, or replace it.
19. Using a vernier caliper, measure the thickness of the brake disc at several points along the generatrix. If necessary, grind the disc or replace it.
20. Lubricate the new guide pin guards with rubber lubricant and slide them over the pins.
21. Put the caliper body on the upper guide pin and turn it down, putting it on the brake pads. Screw in and tighten the bolt of the lower guide pin to the required force.
22. Connect a brake hose to a support and tighten a union bolt with the demanded effort.
23. Bleed the hydraulic brake system.
24. Depress the brake pedal for five seconds.
25. Release the pedal and rotate the front wheel hub ten turns.
26. Using the steelyard, measure the resistance force of the hub to turning.
27. Subtract the result of the first measurement from the result of the second in order to determine the drag force of the brake. The maximum allowable value is 5.7 kG, if it is exceeded, look for jammed components and make the necessary repairs.