The master cylinder used on GM W-Body vehicles is a composite design (plastic fluid reservoir and aluminum body) designed to be used in a diagonally split system (one front and one diagonally opposite rear brake served by the primary piston and opposite the front and rear brakes served by the secondary piston). It incorporates the functions of a standard dual master cylinder plus it has a fluid level sensor and integral proportioning valves. Proportioning valves are designed to provide better front to rear braking balance with heavy brake applications.
The master cylinder fluid reservoir is on the master cylinder and is located under the hood on the left side of the vehicle. The master cylinder reservoir contains enough fluid so it never needs service under normal conditions. A low fluid level sensor in the reservoir will warn of low fluid level. Thoroughly clean the reservoir cap before removal to avoid getting dirt into the reservoir.
REMOVAL & INSTALLATION
Because the vehicles covered by this guide are equipped with ABS, please refer to the ABS Hydraulic Modulator/Master Cylinder removal and installation procedure, located later in this information. Please note that a Tech 1® or equivalent scan tool is recommended for bleeding the system. GM specifies that when any brake component is repaired or replaced such that air is allowed to enter the brake system, the entire bleeding procedure MUST be followed. Unapproved or partial bleed procedures can allow air to remain in the brake system. This could result in reduced braking performance and possible personal injury. In addition, the scan tool is required to scan the entire ABS system for Diagnostic Trouble Codes (DTCs).