GM Service Manual Online
For 1990-2009 cars only

This brake master cylinder is a composite design (plastic reservoir and aluminum body) incorporating a conventional front to rear brake system split. The master cylinder primary piston provides the fluid pressure to the front disc brakes, while the secondary piston provides the fluid pressure to the rear drum brakes. If pressure is lost from either system, the remaining system will function to stop the vehicle.

A quick take-up feature provides a large volume of fluid to the brakes at low pressure with initial brake application. The low pressure fluid quickly provides the displacement requirements created by the seal retraction of the front brake pistons into the front calipers and the retraction of rear brake primary and secondary shoes.

The composite master cylinders have plastic reservoirs. The plastic covers used with these snap into place. A diaphragm is located between the cover and reservoir to keep contaminants out.

The reservoir has two windows which allow the brake fluid to be checked without removal of the brake master cylinder reservoir cover.

The master cylinder reservoirs must be kept properly filled. Too low of a fluid level can allow air to enter the hydraulic system.