2010 GMC Yukon Brake Booster

You can secure the mounting flange of the Brake Master Cylinder in a bench vise so that the rear of the primary piston is accessible, remove the master cylinder reservoir cap and diaphragm, install suitable fittings to the master cylinder ports that match the type of flare seat required and also provide for hose attachment, install transparent hoses to the fittings installed to the master cylinder ports, then route the hoses into the master cylinder reservoir, fill the master cylinder reservoir to at least the half-way point with GM approved brake fluid from a clean, sealed brake fluid container, ensure that the ends of the transparent hoses running into the master cylinder reservoir are fully submerged in the brake fluid, depress and release the primary piston as far as it will travel, a depth of about 25 mm (1 in), several times, observe the flow of fluid coming from the ports. As air is bled from the primary and secondary pistons, the effort required to depress the primary piston will increase and the amount of travel will decrease, continue to depress and release the primary piston until fluid flows freely from the ports with no evidence of air bubbles, remove the transparent hoses from the master cylinder reservoir, install the master cylinder reservoir cap and diaphragm, remove the fittings with the transparent hoses from the master cylinder ports. Wrap the master cylinder with a clean shop cloth to prevent brake fluid spills, and remove the master cylinder from the vise.

If the brake system warning lamp remains illuminated, do not allow the vehicle to be driven until it is diagnosed and repaired. If the brake pedal feels spongy, repeat the bleeding procedure. If the brake pedal still feels spongy after repeating the bleeding procedure, you should inspect the brake system for external leaks, pressure bleeds the hydraulic brake system to purge any air that may still be trapped in the system.