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R there 2 proportioning, distribution valves

886 Views 6 Replies 4 Participants Last post by  duffner
For a 70BB I have the valve on the rear frame but isn't there another valve thingamabob under the Master Cylinder? Yes, I took it apart years ago and don't have it anymore; just have my new MC and Booster. Thanks....
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Yes the front valve is the disk hold off and the rear is a prop valve.

On my 69, I removed the hold off valve because it was sucking air. I just put a fitting in its place, and the brakes work great.

1967-70 GM Hold Off Valve

This is the hold-off valve that mounts on the stud of the master cylinder on all factory 1967-70 disc brake cars. It is used in conjunction with the distribution block mounted on the frame, which is the same on factory disc and drum cars. This valve holds off the front brakes to give time for the rears to activate. At a calibrated pressure, the valve allows fluid to pass and engages the front brakes. This valve is the same on all GM cars, but the bracket is different for applications NOT listed.

The rear was a correction valve or rear hold off.

In 71 they started using the combination valve.
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