GMC 18007935 Repair Kit, Brake Mast Cyl

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Before dismantling, it is advisable to purchase a Brake Master Cylinder overhaul kit that includes all the necessary replacement parts, particularly the rubber seals, to ensure proper fluid control within the Brake Master Cylinder. During the rebuild procedure, be cautious not to allow grease or mineral-based solvents to contact the rubber parts. To protect painted surfaces from brake fluid spills, cover the front fender and cowling area of the car. Start by disconnecting the electrical lead from the brake failure warning switch and then disconnect the brake line connections, using rags or newspapers to soak up the fluid that will drain out. For manual brake setups, disconnect the Brake Master Cylinder pushrod from the brake pedal inside the car. Remove the two Brake Master Cylinder mounting nuts, take out the Brake Master Cylinder from the car, and drain any remaining fluid. Remove the brake failure warning switch and the two proportioner valves, noting their respective positions as they are different. For further disassembly, it is helpful to place the Brake Master Cylinder in a vice with blocks of wood on either side to avoid overstressing the aluminum body. Use an Allen wrench to remove the switch piston plug and extract the switch piston assembly from the bore. Next, remove the primary piston retaining ring and then the primary and secondary piston assemblies. Also, remove the plastic reservoir and the quick take-up valve retaining ring, and clean all parts in denatured alcohol, avoiding gasoline or mineral-based solvents that could damage the rubber seals. Inspect the cylinder bore for any imperfections and use crocus cloth if needed, rinsing the bore with clean brake fluid afterward. Replace the old seals with new ones, lubricate the bore with brake fluid, and reassemble the primary piston assembly. Similarly, disassemble and install new 0-rings and retainers for the switch piston assembly before putting it back into the cylinder. Install new 0-rings on the proportioner valves and the failure warning switch, and insert the quick take-up valve into the cylinder body with its retaining ring. Press new reservoir grommets into the cylinder body, place the reservoir top down on a flat surface, and press the cylinder body onto it with a rocking motion. Install the cylinder on its mounting studs and reconnect the Brake Master Cylinder pushrod (for manual brake setups) and the brake line connections, torquing them to specs. Reconnect the electrical lead to the failure warning switch. Fill the Brake Master Cylinder reservoir with brake fluid and bleed the brake system. Finally, install the reservoir diaphragm and cover, and test drive the car while checking for proper braking performance and leaks.

Use compressed air to force out the secondary piston, spring, and retainer.

The brake master cylinder is located under the hood, in the left rear section of the engine compartment.

Assemble primary and secondary seals along with the protector. Insert the assembly into the cylinder and seat the spring against the bore.

Care should be taken not to spill any brake fluid on painted surfaces, as it can eat paint.

Remove the brake failure warning switch and the two proportioner valves, noting their respective positions as they are different. Place the master cylinder in a vice with blocks of wood on either side to avoid overstressing the aluminum body. Use an Allen wrench to remove the switch piston plug and extract the switch piston assembly from the bore. Remove the primary piston retaining ring and then the primary and secondary piston assemblies. Also, remove the plastic reservoir and the quick take-up valve retaining ring.

To overhaul and install the master cylinder, mount it in a padded vise and remove the primary piston lock-ring by depressing the piston and prying the ring out. Then, remove the primary and secondary piston assemblies, as well as the reservoir and grommets. Inspect the cylinder bore for damage, and if found, replace the master cylinder body. Lubricate and press the new reservoir grommets into place, then attach the master cylinder body to the reservoir using a rocking motion.

Unbolt the isolation/dump valve and RWAL module mounting bracket, then plug the brake line ends to prevent contamination. Remove the two master cylinder mounting nuts and move the bracket aside slightly, taking care not to kink the hydraulic lines. Finally, remove the master cylinder from the vehicle and discard any remaining fluid in the reservoir after removing the reservoir cover and diaphragm.

Purchasing a master cylinder overhaul kit is important as it includes all the necessary replacement parts, particularly the rubber seals, to ensure proper fluid control within the master cylinder during the rebuild procedure.