Brakes on 1977 Oldsmobile 88

My wife owns a 1977 Oldsmobile 88 with about 93,000 miles. It has been driven only occasionally and intermittently for the past 15 years. Recently, it leaked brake fluid, causing the brake warning light to come on. I took it to a mechanic, who bled the lines but could not find the leak. After driving it for perhaps 25 miles, the brake warning light came on again. The brake fluid was low again, so I took it to a different mechanic at Meineke. He found a leak in the rear brake lines, replaced them, refilled the fluid reservoir and bled the lines. However, the brake warning light still came on whenever the car was started. He then checked the parking brake to assure that it was not the problem. He bled the lines again and the problem still remained. He looked some more and finally concluded that the problem was in the proportion valve, which he said needed to be replaced. Unfortunately, that part seems to be completely unavailable from GM, its dealers and any independent parts dealers that he or I have been able to contact.

The brakes seemed to work satisfactorily when I drove the car back from the mechanic?s garage. However, with the brake warning light on, the car cannot pass the state inspection, so we must either find a way to get it repaired or dispose of it. The only suggestion that the mechanic offered was to get a proportion valve from a junkyard. But the junkyards I contacted said that they did not remove that part and I would have to find a comparable car and remove it myself, which I am unable to do. In any even, none of them actually had a 1977 Oldsmobile 88 in their yards.

I have the following questions and would appreciate any advice: (1) Since the proportion valve had given no trouble before, is that really likely to be the problem? Is it likely that the mechanic, in replacing the rear brake lines, did something to cause the problem? (2) If the problem is actually in the proportion valve, is it likely that the existing part can be repaired? (3) If we must replace the proportion valve, can you offer any suggestions as to how to find one? For example, what other models or years of GM cars used the identical part.

Any advice would be greatly appreciated.

Harry S. Havens


Alexandria, Virginia.

Did they pressure bleed the brake system? If so they may have forgotten to set up the proportioning valve for pressure bleeding. On some valves there’s a rubber button on the front of the valve that has to be depressed while pressure bleeding. And on others a special clip is slipped under the pin at the front of the valve to hold it out 1/16th of an inch while pressure bleeding. If this isn’t done while pressure bleeding the system, the proportioning valve won’t center itself and the brake light keeps coming on.


Centering the brake failure warning light. Bleed the rear brakes until the light comes on and stays on. Then carefully bleed one of the FRONT brakes until the light blinks off. Close the bleeder right there! Have a helper in the car watch the light as he is pushing the pedal down. When it blinks off, have him holler NOW! Tighten the bleeder, release the brake pedal, pump it a few times, the light should remain off…

…or disconnect the warning light wire to the proportioning valve.

THanks, Tester. I will try to find out if the mechanic did this properly. Havenshs

Thanks, Caddyman. The mechanic did this while I was watching. It didn’t solve the problem. Havenshs

THanks, Circuitsmith. My concern with this is that disconnecting the warning light wire from the valve would probably disable the warning light. If that did not come on when the ignition is switched on, it would fail the state inspection. If you think it would not disable the warning light, I would give it a try. Havenshs

That light is not part of the state inspection. There is no computer in your car to control warning lights. It’s either on or off. A few rare inspectors might check to see if the light comes on with the e-brake, but disconnecting it at the proportioning valve will not disable that… They will fail you if they see the light on, but normally it’s off…

Caddyman. If nothing else solves the problem, I will try disconnecting the wire. However, if the proportioning valve is not working properly, will that result in future uneven wear on the brakes? Havenshs

Some repair shops might go remove the part for you.