# Proportioning valve



## tjs72goat (Jul 20, 2017)

Can the newer style proportioning valve be used on the frame at an angle where the stock one resided? I know they generally get mounted by the master cylinder. I just wonder about the shuttle valve if it ever has to be centered for some reason, it wouldn't be easily accessible.


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## BearGFR (Aug 25, 2008)

There's a lot of confusion about the various 'valves' and stuff that were in the brake systems on these cars. It didn't help that GM did different things in different years. For front disc cars in some years there was a hold off valve, a proportioning valve, and a distribution block/valve. The hold off valve's job was to prevent the rear brakes from locking up before the front brakes were working. The proportioning valve balanced braking action between front and rear, and the distribution block's only function was to act as a switch to detect a pressure imbalance between front and rear and turn on a light if one was detected. It's main job was to alert you to the possibility of a leak in either the front or rear brake system in cars that had dual master cylinders. That's the brass more or less rectangular block that mounts down low on the inside of the driver's side frame rail and has a wire connection "in the middle". The distribution block/switch works off of brake line hydraulic pressure, which is considerable - so mounting it at an angle instead of "flat" shouldn't be a problem if that's what you're asking.

Bear


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## tjs72goat (Jul 20, 2017)

Thanks Bear. Yes, I wondered if the shuttle valve can inadvertently slide before brakes are bleed and have pressure applied if mounting at an angle. It would be cumbersome to get to in the stock area if a problem. And yes, I guess that would be a distribution block. 
It's odd the stock one mounted on the frame was just for a light. I couldn't bleed my brakes because nothing would go through this. My understanding is, if front or rear detects a leak or pressure difference, the shuttle valve moves to cut that system off so you still have brakes and not lose all pressure/fluid.


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