Master Cylinder Replacement (Vacuum Boost)

Master Cylinder Reservoir Filling (Two-mode Hybrid)
Warning: Refer to Brake Fluid Irritant Warning (Brake Fluid Irritant Warning) .

Caution: Refer to Brake Fluid Effects on Paint and Electrical Components Caution (Vehicle Damage Warnings) .







Important: The ignition must be in the OFF position, without pausing at ACCESSORY, and without applying the brake pedal to ensure the brake modulator and high pressure accumulator (HPA) pressure relief occurs. This process will take approximately 1 to 3 minutes.


1. Turn the ignition to OFF, without pausing at ACCESSORY, and remove the ignition key.

Important: During the pressure relief process, the fluid level in the master cylinder reservoir will rise. Do not remove the master cylinder reservoir cap during the pressure relief process.


2. Wait approximately 1 to 3 minutes until the brake modulator and HPA pressure relief is complete.
3. Visually inspect the brake fluid level through the brake master cylinder reservoir.
4. The brake fluid level should rise to the upper full fill level mark (1) after the brake fluid level stabilizes.
5. If the brake fluid level is below or rises above the upper fill level mark after the brake fluid level stabilizes, the brake system should be inspected.
6. If the brake fluid level is at the upper fill level mark, do not add brake fluid to the master cylinder reservoir.
7. Start the engine.
8. As the brake modulator draws brake fluid from the master cylinder reservoir to charge the brake modulator and the HPA, the brake fluid level will decrease.
9. The brake fluid level should be at or above the midway point of the MAX and MIN level marks (2) of the master cylinder reservoir after the brake fluid level stabilizes.
10. If the brake fluid level is at or below the midway point of the MAX and MIN level marks on the master cylinder reservoir after the brake fluid level stabilizes, the brake system should be inspected for wear and possible brake fluid leaks.
11. If the brake fluid level is at or below the midway point of the MAX and MIN level marks on the master cylinder reservoir point during routine fluid checks, and an inspection of the brake system did not reveal wear or brake fluid leaks, the brake fluid may be filled to the MAX level mark.
12. If brake system service was just completed, brake fluid should be added to bring the level in the master cylinder reservoir the MAX level mark.
13. If the brake fluid level is at the MAX level mark, adding brake fluid is not recommended under normal conditions.
14. If brake fluid is to be added to the master cylinder reservoir, clean the outside of the reservoir on and around the reservoir cap prior to removing the cap and diaphragm. Use only Delco Supreme 11(R), GM P/N 12377967 (Canadian P/N 992667), or equivalent DOT-3 brake fluid from a clean, sealed brake fluid container.