GM Buick/Oldsmobile/Pontiac/Full-Size 1975-1990 Repair Guide

Brake Master Cylinder



When making additions of brake fluid, use only fresh, uncontaminated brake fluid which meets or exceeds DOT 3 standards (as stated on the container).


See Figures 1, 2, 3 and 4

The brake master cylinder is located under the hood, in the left rear section of the engine compartment. It is divided into two sections (reservoirs) and the fluid must be kept within 1 / 4 in. (6.3mm) of the top edge of both reservoirs or between the MAX. and MIN. level markers. The level should be checked at least every 7,500 miles.

Any sudden decrease in the level of fluid indicates a possible leak in the system and should be checked out immediately.

To check the fluid level, simply pry off the retaining bail or lift the retaining tabs and then lift off the top cover of the master cylinder. Be careful not to spill any brake fluid on painted surfaces, as it eats paint. Do not allow the brake fluid container or the master cylinder reservoir to remain open any longer than necessary; brake fluid is hygroscopic (absorbs moisture from the air), reducing its effectiveness and causing corrosion in the lines.

The reservoir cover on some later models may be without a retaining bail. If so, simply pry the cover off with your fingers.

Click image to see an enlarged view

Fig. Fig. 1: Late model fluid reservoir showing fluid level marks

Click image to see an enlarged view

Fig. Fig. 2: To fill the reservoir, first pry the cover open

Click image to see an enlarged view

Fig. Fig. 3: Remove the rubber gasket

Click image to see an enlarged view

Fig. Fig. 4: Add fluid to the proper level