I am at the end of changing from power drums to a factory power disk/drum set-up. I have fluid flowing to all 4 wheels, but the pin in the pro[portioning valve is pushed in and won't come back out.


I have beat on the valve with a hammer after spraying with brake clean. I have opened both front bleeders and jammed the brakes, but nothing has released the pin.


Is it time to replace the original proportioning valve I got from the donor car with the rest of the disk brake parts? It should be spring loaded, right?

 

I'm assuming you are referring to the round valve by the master cylinder? If so it is referred to as a Hold Off Valve and was used on 67-70 Cutlass models. In the CSM, the plunger on the back, which should have a rubber boot over it, is depressed when bleeding the brakes although I have not done so in the past. If it is stuck, then chances are the valve is rusted internally and will not function correctly. You can try to take it apart and clean it up but you may need to replace a few rubber parts. I though I saw where someone posted recently that they found OEM rebuild kits for the valve but I'm not 100% certain. Do a search and see what you can find. You can also by a reproduction valve too. When using this Hold Off Valve, you will use the same metering block on the frame as was originally on your car with the drum brakes. Do not use a 71 and newer valve. Those are called proportioning valves beginning in 71 as the Hold Off Valve function was combined into the metering block to have one part located on the frame.

Brian

 

Mine is a 1972. It doesn't have the Hold Off Valve by the master cylinder. I replaced the Distribution Block from the original power drum brakes with a Proportioning Valve (SM calls it a Combination Valve) from another 72. I put a clip on the pin to hold it in to bleed, but it remains pushed in. I have done everything I can think of to make it pop out, but as you suggest, it must be rusted inside. I guess it is called a Combination valve because it combines the proportioning with the hold off. I have the separate Hold Off Valve on my 1970 Bonneville with power disk brakes. I guess it is time to get one from InLine.

 

If all 4 lines are able to bleed then what exactly is the problem? The shuttle "pin" is only supposed to move and stick in the front if it detects a loss of press sure in one or the other bank. If all 4 bleed then its centered in the bore as it should be.

I don't think you have a problem.

I've had repop valves that stick and you cant bleed the brakes... or worse the shuttle itself leaks from the front. But doesn't sound like you have those problems.

B