Functional check
1. Without starting the engine, depress the foot brake pedal several times. Check that there is no change in pedal back travel (distance between pedal and floor).
2. Keeping the pedal depressed, start the engine. If immediately after starting the pedal slightly "fails", therefore, the vacuum brake booster is working properly.
Leak test
1. Run the engine for a couple of minutes, then shut it off. Slowly depress the foot brake pedal several times. If at first the pedal stroke is gradually reduced with each squeeze, however, after three or four strokes it stabilizes, the tightness of the vacuum booster assembly is not broken.
2. Depress the foot brake pedal while the engine is running. Keeping the pedal depressed, stop the engine. If after 30 seconds of keeping the pedal depressed, its reserve stroke does not change, therefore, the tightness of the vacuum booster assembly is not broken.
Withdrawal
1. The vacuum brake booster unit cannot be repaired and must be replaced as an assembly in case of failure.
2. Remove the GTZ assembly from the vacuum booster (see Section Removal and installation of the main brake cylinder).
3. On models with manual transmission, remove the clutch master cylinder (see chapter Clutch and drive shafts).
4. Disconnect the vacuum hose going to the amplifier from the engine. Be careful not to damage the hose when removing it from the fitting on the booster assembly.
5. On 4-cylinder models, remove the intake air temperature sensor (IAT) (see chapter Engine management).
6. Under the instrument panel, find the connection point for the vacuum booster pusher rod to the foot brake pedal.
7. Remove the cotter pin and disconnect the pusher from the pedal.
8. From the cabin side, give four nuts securing the vacuum booster assembly to the bulkhead of the engine compartment, remove the washers (use a flashlight if necessary).
9. Go to the engine compartment and remove the rear bulkhead vacuum booster assembly. After the amplifier mounting studs are completely out of the holes in the bulkhead, begin to turn the assembly to the right (to the center line of the car), thereby ensuring the release of the pusher tip from the bulkhead. Remove the assembly from the engine compartment.
Installation
1. Installation is carried out in the reverse order to dismantling. Make sure that all fasteners are tightened to the required torque, and that the pins and cotter pins are replaced.
2. When installing a new brake booster, it is necessary to adjust the working clearance of its pusher rod, for which:
- a) Using a manual vacuum pump, create a vacuum on the amplifier to a depth of 508 mm Hg. Art., then measure the protrusion of the pusher above the assembly surface mating with the GTZ (including gasket, if any). Record the measurement result, call it "Size A".
- b) Measure the distance from the GTZ support flange to the end surface of the cylinder. Write down the result of the measurement, designating it: "Size B".
- c) Measure the distance from the end surface of the GTZ to the bottom of the landing pocket at the end of its piston. Record the result by calling it: "Size C".
- d) Subtract dimension B from dimension C, then subtract dimension A from the resulting difference. The result obtained will determine the value of the required working clearance.
- e) Compare the calculation result with the requirements of the Specifications. Make appropriate adjustments if necessary.
3. To adjust the operating clearance of the pusher rod, loosen the toothed locknut and turn the adjuster in the appropriate direction. After completing the adjustment, tighten the locknut and re-measure the clearance. Repeat if necessary.
4. After installing the GTZ, bleed the brake system (see Section Bleeding the brake system).