Removal and installation the master brake cylinder (Opel Astra G)

A failed brake master cylinder must be replaced. Manufacturers do not recommend attempting to perform a refurbishment of the brake master cylinder.

Removal

The brake master cylinder is located in the engine compartment of the vehicle and is attached to the brake booster assembly.

1. Press the foot brake pedal several times to release any residual pressure in the system zafira models remove the plastic cover at the rear of the engine compartment.

2. Pump out as much of the fluid as possible from the master cylinder reservoir (use a syringe or a rubber bulb).

3. Place rags under the fittings and have caps or plastic bags available to plug the open ends of the brake lines to prevent dirt from entering the system.

Brake fluid is an aggressive chemical compound and when in contact with body panels it destroys the paintwork. Before starting the procedure, cover the fenders and the front panel of the car with special covers or just old blankets.

4. If equipped, disconnect the electrical wiring of the brake fluid level switch sensor from the brake master cylinder reservoir.

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5. Loosen the nuts of the union assemblies connecting the brake lines to the master cylinder. To avoid rounding the splines of the nuts, loosen them using a special open-end wrench with a slotted head. Pulling slightly outward, separate the brake lines from the unions of the master cylinder. Immediately plug the open ends of the tubes.





6. Disconnect the clutch hydraulic line tube from the master cylinder reservoir - immediately plug the open end of the tube.

7. Loosen the two retaining nuts and separate the master cylinder from the brake booster assembly. Remove the cylinder from its retaining studs and lift it out of the engine bay, being careful not to spill the hydraulic fluid filling the cylinder onto the painted body panels. Remove the sealing gasket.



8. If necessary, carefully pry the clamps with a screwdriver, release them and remove the brake fluid reservoir from the master cylinder assembly. Remove the reservoir seat bushings from the holes in the cylinder - the bushings must be replaced without fail.

Installation

1. Before installation, the new brake master cylinder must be bled on a workbench. For convenience, clamp the cylinder mounting flange in a vice with soft jaws. Then 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 a special bleeding kit to the master cylinder outlet fittings (ask in car accessories stores).



3. Fill the reservoir with fresh brake fluid of the required grade (see Chapter Routine maintenance).

4. Slowly push the pistons into the cylinder (it will be most convenient to use a large Phillips-head screwdriver), - air should start to exit the pump chambers into the reservoir. It is important that the ends of both tubes are completely immersed in the brake fluid in the reservoir to eliminate the possibility of it being sucked back into the cylinder when the pistons are released.

5. Continue pumping until the liquid being pushed out through the tubes is completely free of air bubbles.

6. Disconnect the tubes one by one, immediately sealing the open ends of the fittings. Close the master cylinder reservoir with a lid.

7. Place the brake master cylinder on the studs on the vacuum booster assembly (don't forget to replace the sealing gasket) and, for now only by hand, tighten the fastening nuts.

8. Screw the brake line nipples into the cylinder. Since the cylinder is not yet firmly secured, its position can be adjusted slightly to make it easier to screw in the nipples - try not to strip the threads.



9. Tighten the brake master cylinder mounting nuts to the required torque, then tighten the nipple connections securely.

10. Fill the brake master cylinder reservoir with fresh brake fluid and bleed the hydraulic system (see Bleeding the brake system). For bleeding the master cylinder on a car (if you haven't done it on the workbench) you will need an assistant to operate the foot brake pedal. Ask the assistant to press the pedal several times, then lock 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 fluid being pushed out is completely free of air bubbles. Proceed in a similar manner to bleed the second union.

Keep a clean rag handy to immediately remove any traces of brake fluid that gets on painted body surfaces.

11. Before operating the vehicle, make sure that the brakes are functioning properly.