Attention! Before proceeding with the procedures, carefully read the warning text at the beginning of the Section System design, description of individual components and mechanisms.
When assembling, you will need new mounting nuts and an o-ring.
Removing
Models without ABS
1. Thoroughly wipe the surface of the GTZ reservoir and remove the cap from it. Remove the filter and pump out the hydraulic fluid from the reservoir.
Note. In no case do not suck the brake fluid with your mouth - use a syringe or a rubber bulb! Alternatively, open either brake bleed valve, connect a drain hose to it, and empty the reservoir by pumping fluid into the drain pan by depressing the foot brake pedal.
2. Release the retaining tab of the reservoir and remove the latter from its support bushings on the GTZ.
3. Wipe the cylinder wall surfaces around the brake line fittings. Place a rag under the spillage fittings. Remembering the order of connecting the pipes, loosen the union nuts and disconnect the lines. Seal open ends of pipes and fittings immediately to minimize brake fluid loss and prevent dirt from entering the system. Pick up any spilled liquid with a rag.
4. Give nuts of fastening ГТЦ on the block of the servo drive of the vacuum booster of brakes, remove washers.
Note. During assembly, the nuts must be replaced without fail.
5. Remove the GTZ from the vacuum booster servo unit along with the O-ring.
Note. The sealing ring must be replaced during assembly.
6. Due to the lack of replacement internal components for sale, it is not possible to overhaul a failed GTZ. Replace the defective assembly with a new one. The only components to be replaced are the rubber bushings on the tank GTZ mounts. Both bushings are simply tightly planted in their sockets.
ABS equipped models
Note. On models equipped with ABS, be sure to disconnect the battery before disconnecting the hydraulic brake lines. Connect the battery only after connecting all the hydraulic lines of the brake path. Violation of this requirement is fraught with air entering the hydraulic modulator, the removal of which during the normal bleeding of the system (see the text of Section) is not possible and requires the use of a special electronic tester (VAG 1552).
1. Disconnect the negative cable from the battery, then remove the cap from the GTZ reservoir. Drain the hydraulic fluid from the reservoir.
Note. In no case do not suck the brake fluid with your mouth - use a syringe or a rubber bulb!
2. Remove the fixing pin of the retainer tab and carefully remove the tank from the GTZ body, releasing it from the rubber sealing bushings.
3. Wipe the cylinder wall surfaces around the brake line fittings. Place a rag under the spillage fittings. Remembering the order of connecting the pipes, loosen the union nuts and disconnect the lines. Seal open ends of pipes and fittings immediately to minimize brake fluid loss and prevent dirt from entering the system. Pick up any spilled liquid with a rag.
4. Give nuts of fastening ГТЦ on the block of the servo drive of the vacuum booster of brakes, remove washers.
Note. During assembly, the nuts must be replaced without fail.
5. Release the hydraulic modulator support bracket from the servo block, then remove the GTZ with the o-ring.
Note. The sealing ring must be replaced during assembly.
6. Due to the lack of replacement internal components for sale, it is not possible to overhaul a failed GTZ. Replace the defective assembly with a new one. The only components to be replaced are the rubber bushings on the tank GTZ mounts. Both bushings are simply tightly planted in their sockets.
Overhaul
1. Brake fluid leaks developing between the GTZ flange and the brake booster servo housing, or an increase in foot brake pedal travel, indicate the need for a major overhaul of the cylinder assembly. Repairs are recommended to be carried out in a workshop workshop.
2. Remove GTZ.
3. Release the brake fluid reservoir from the bushings of the GTZ receiving sockets.
4. Remove the rubber bushings from the sockets.
5. Remove the piston stroke limiting pins from the cylinder inlets - just turn the assembly upside down and shake.
6. Turn the cylinder vertically and, striking the landing flange on a wooden block, alternately knock out one piston from it, then the second.
7. Carefully inspect the mating surface of the cylinder body for cavities and mechanical damage. Minor defects can be removed by grinding with a fine-grained polishing paste. After sanding is complete, wipe the treated surface with methanol. In case of more severe damage, the cylinder must be replaced.
8. Wash all removed components in clean brake fluid or methyl alcohol.
Note. Never use gasoline or other petroleum-based solvents to flush GTZ components, as contact will destroy the rubber elements. After flushing, carefully examine the condition of the parts, paying special attention to the elasticity of the piston cuffs (to remove old cuffs from the pistons, you can use a screwdriver; the use of a screwdriver to install new cuffs will lead to irreversible failure).
9. Also check the condition of the rubber bushings removed from the sockets for landing connecting pipes of the brake fluid reservoir.
10. After replacing worn or failed components, you can start assembling the device (see below).
11. Moisten a mirror of the cylinder with a pure brake liquid.
12. Install the sealing collars on the pistons, and the washers on their rods for installing the springs.
13. Put the return spring on the shorter piston rod (end face of a smaller diameter [coils with a short pitch?] forward). Insert the piston and spring assembly into the cylinder (spring forward). With a drift against the bottom of the piston, compress its spring approximately 0.5 cm and, holding the assembly in this position, fill the appropriate stroke limit pin into the inlet.
14. Acting in a manner similar to that described in the previous paragraph, put the return spring on the second piston rod. Insert the piston and spring assembly into the cylinder (spring forward). Insert a drift into the recess in the end of the piston and, overcoming the resistance of the spring, deepen the piston approximately 2 cm below the mating surfaces of the mounting flange. While holding the piston in this position, insert the thrust pin into the second cylinder inlet.
15. How many times by pressing the drift, check the freedom of movement of the pistons in the cylinder.
16. Remove the drift and force the rubber bushings into the holes for the stop pin.
17. Before installing the GTZ assembly, check the protrusion of the adjusting tip of the pusher rod of the vacuum booster servo drive and the depth of the piston in the cylinder (distance from the mating surfaces of the flange to the bottom of the recess in the piston). The difference between the results of the first and second measurements should be 0.3÷0.6 mm. The presence of such a gap is a prerequisite for the proper functioning of the GTZ and the vacuum amplifier. Gap adjustment is achieved by rotating the tip at the end of the push rod. Note: In the conditions of a workshop of a service station, the installation clearance of the pusher is determined using a special device.
18. Now you can start installing the assembly.
Installation
1. Thoroughly clean the mating surfaces of the GTZ and the vacuum booster block. Install a new O-ring into the groove on the back of the cylinder body.
2. Place the GTZ on the vacuum booster block. Make sure the servo follower rod fits into the center of the cylinder piston. Install washers, screw on new mounting nuts and tighten them to the required torque.
3. Wipe the fittings of the brake pipes and connect the latter to their original places to the GTZ. Tighten the flare nuts securely.
4. Lightly lubricate the rubber sealing bushings in the upper part of the GTZ with fresh brake fluid and firmly seat the hydraulic fluid reservoir in them. Secure the reservoir to the cylinder by snapping the retainer tab.
5. Fill the GTZ reservoir with fresh hydraulic fluid (up to the MAX mark) and perform a complete bleeding of the hydraulic system (see Section Bleeding the hydraulic system). Replace the tank cover. Before starting the operation of the vehicle, check the correct functioning of the brake system.
ABS equipped models
1. Thoroughly clean the mating surfaces of the GTZ and the vacuum booster block. Install a new O-ring into the groove on the back of the cylinder body.
2. Having moved the hydraulic modulator away from the vacuum booster servo unit, install the GTZ in its regular place. Make sure that the servo push rod fits into the center of the cylinder piston. Replace the modulator by placing its bracket on the studs of the vacuum booster unit, then install the washers, screw in new fixing nuts and tighten them to the required force.
3. Lightly lubricate the rubber sealing bushings in the upper part of the GTZ with fresh brake fluid and firmly seat the reservoir in them. Secure the reservoir to the cylinder by installing the lock pin.
4. Before connecting the brake lines, bleed the air from the master cylinder. To do this, fill the GTZ with fresh hydraulic fluid and place a drain container under the fittings. Ask an assistant to depress the foot brake pedal several times at intervals of 5 seconds. When liquid free from air bubbles begins to be pushed out of the cylinder, pumping can be stopped. Pour fluid into the brake pipes as well. Ask an assistant to depress the pedal and fix it in the lower position and connect the brake pipes to the cylinder. Tighten the flare nuts securely. After connecting both tubes, the pedal can be released. Remove the waste container and wash off the splashes with clean cold water.
5. Fill the GTZ reservoir with fresh hydraulic fluid (up to the MAX mark) and perform a complete bleeding of the hydraulic system (see Section Bleeding the hydraulic system). Replace the tank cover. Before starting the operation of the vehicle, check the correct functioning of the brake system.