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69 GS Brake Issue


Stu Allen
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I'm working on my '69 Riviera GS trying to fix a intermittent brake tell-tale light that comes on when you depress the pedal and then goes out. This problem was there when I bought the car last winter.  The brakes seem to operate just fine but the light is cause for concern. I replaced one rear wheel cylinder that had a twisted off bleed screw and bled the rear brakes. When I went to check the front Bendix disc brakes I checked the '69 Buick chassis service manual (section 50-32) and became confused. The text says the metering valve must be held open to bleed the brakes by depressing the stem yet the schematic (figure 50-59) shows the valve is open when the stem is in the extended position. When I bleed the front brakes with the Mitivac pump I get a steady flow with no bubbles leaving the metering valve in its extended position.  Did I do it correctly?

The problem still exists so I may have to rebuild the master cylinder.  Randy Hunter tells me I may need to replace the brake pipe distributor switch (any idea of where to find a new one?) and suggested I might get some advice by posting here on the forum. Any suggestions you have would be greatly appreciated.

Stu Allen

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Not sure about 69 as I don't have that manual. Any way you could scan and post the diagram of the valve?

The standard process in 71-73 is to depress the pin on the combination valve while bleeding fronts. Since the light comes on and goes out you may have a system pressure imbalance between front and rear and the switch is doing what its designed to. Perhaps there is a problem in the master cylinder causing a pressure differential. Or the valve might just be bad. I am not aware of any sure way to test the valve. Are you certain all wheels are braking evenly?

 

If your master has been on the car awhile its usually a good expenditure to replace it and better yet get a stainless or brass sleeve installed. Even if the MC doesn't solve the problem, you know the master is new. A sleeved MC is far superior to anything you will buy in the aftermarket. Since disc brakes were not that common in 69, not sure what type of valve it has or if it might even be serviceable, though many aren't. If not you would need to find used which would be difficult not to mention knowing if the used valve is good or not prior to installation. 

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Problem fixed! I removed the pressure metering valve and found that the stem that protrudes at the rear of the valve was seized. I tore the valve apart, removed the stem and cleaned it up, put it back together and reinstalled it.As usual I had to make new lines as the tubing twisted off with the fittings. After bleeding the front brakes again, the light goes out and the brakes function well.

Thanks for the advice on the problem.

Stu

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