A failed GTZ must be replaced. Manufacturers do not recommend attempting to rebuild the brake master cylinder.
Removing
The master brake cylinder is located in the vehicle's engine compartment and is attached to the brake booster assembly.
1. Depress the foot brake pedal several times to release residual pressure in the system. On Zafira models remove the plastic trim at the rear of the engine compartment.
2. Pump out as much liquid as possible from the GTZ tank (use a syringe or rubber bulb).
3. Place a rag under the fittings and prepare caps or plastic bags to seal the open ends of the brake lines to prevent dirt from entering the system.
Brake fluid is one of the aggressive chemical compounds and, in contact with body panels, destroys the paintwork. Before proceeding with the procedure, cover the wings and front panel of the car with special covers, or just old blankets.
4. With the appropriate configuration, disconnect the electrical wiring of the sensor-switch of the brake fluid level from the GTZ tank.
5. Loosen the nuts of the fitting units for connecting to the GTZ of the brake lines. To avoid rounding of the splines of the nuts, use a special box wrench with a split head to loosen them. Slightly pulling outward, separate the brake lines from the master cylinder fittings. Seal the open ends of the tubes immediately.
6. Disconnect the tube of the hydraulic clutch path from the GTZ reservoir - immediately plug the open end of the tube.
7. Release two fixing nuts and separate the main cylinder from assembly of the brake booster. Remove the cylinder from the mounting studs and remove it from the engine compartment - try not to spill the hydraulic fluid filling the cylinder onto the painted body panels. Remove the seal.
8. If necessary, carefully prying with a screwdriver, release the latches and remove the brake fluid reservoir from the master cylinder assembly. Remove the tank bushings from the holes in the cylinder - the bushings must be replaced without fail.
Installation
1. Before installation, a new GTZ must be pumped on a workbench. For convenience, clamp the cylinder seat flange in a vise with soft jaws. Next, you will have to simultaneously manipulate the piston in the cylinder and observe the flow of brake fluid pushed out through the outlet fitting. Install the brake fluid reservoir on the cylinder - do not forget to replace the bushings.
2. Connect a pair of tubes from the special bleed kit to the GTZ outlet fittings (ask at car accessories stores).
3. Fill the reservoir with fresh brake fluid of the correct grade (see chapter Current service).
4. Slowly push the pistons into the cylinder (It is best to use a large Phillips screwdriver), - air should begin to exit the pressure chambers into the tank. At the same time, it is important that the ends of both tubes are completely immersed in the brake fluid in the reservoir in order to exclude the possibility of sucking it back into the cylinder when the pistons are released.
5. Continue pumping until the fluid pushed through the tubes is completely free of air bubbles.
6. Disconnect the tubes one by one, plugging the open ends of the fittings immediately. Close the GTZ tank with a lid.
7. Place the GTZ on the studs on the vacuum booster assembly (don't forget to replace the gasket) and, while only by hand, tighten the fixing nuts.
8. Screw the fittings of the brake lines into the cylinder. Since the cylinder is not yet completely fixed, its position can be slightly corrected in order to facilitate the screwing of the fittings - try not to strip the threads.
9. Tighten the GTZ mounting nuts with the required force, then tightly tighten the union connections.
10. Fill the GTZ reservoir with fresh brake fluid and bleed the hydraulic system (see Bleeding the brake system). For pumping the GTZ on a car (if you haven't done it on a workbench) you will need the help of an assistant who will manipulate the foot brake pedal. Ask an assistant to depress the pedal several times, then fix it in the lower position. Loosen the union nut, releasing the mixture of air and brake fluid from the cylinder. Repeat the procedure until the ejected fluid is completely free of air bubbles. Proceeding in a similar manner, pump the second fitting.
Keep a clean rag handy to immediately remove traces of brake fluid that gets on the painted body surfaces.
11. Before starting the operation of the car, make sure that the brakes are working properly.
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