I have a 71 chevelle that I converted from power drum to power disk..I installed every thing using used prop valve,spindles..and new all other..hard pedal/feels like no power assist..there was alread a booster..I did bench bleed the mc...maybe the prop valve is bad or stuck..the button cant be pushed by hand..too hard..any idea's?

Bypass it to test.

BTW, the button on the front brake valve does not push in. Its resting position is already inward, and it moves outward when the brakes are applied. As it moves outward, it shuts off flow, and then again allows full flow to the front brakes.
It must be held in its resting position while pressure bleeding the front brakes because pressure bleeders operate at the same low pressures the valve does.
An old one can get stuck in any position, causing no or only partial flow to the front brakes, or always full flow.

I have heard of the distribution block being partially stuck or clogged, also causing hard brakes. The true test would be a line pressure test, but bypassing is easy and conclusive to the part bypassed.

Bypass it to test.

BTW, the button on the front brake valve does not push in. Its resting position is already inward, and it moves outward when the brakes are applied. As it moves outward, it shuts off flow, and then again allows full flow to the front brakes.
It must be held in its resting position while pressure bleeding the front brakes because pressure bleeders operate at the same low pressures the valve does.
An old one can get stuck in any position, causing no or only partial flow to the front brakes, or always full flow.

I have heard of the distribution block being partially stuck or clogged, also causing hard brakes. The true test would be a line pressure test, but bypassing is easy and conclusive to the part bypassed.


So if I understand..with the car running and if I apply the brakes the button should kick out?..how do I btpass to test?

There is a line going in, and a line going out of the valve. Connect the two without the valve using a brake union. Bleed brakes. Ta-da, bypassed ;)

If you dont want to bend the original lines to get them to reach each other, you will need a short piece of line replacing the one from the master, probably an adapter to the master, and still the union between the two lines. You should be able to bend the line sufficiently by hand.

The line is 3/16".
The valve's fittings are standard 3/8 threads.
The master front outlet OE is 1/2" threads.
Adapter and union must be for 3/16" inverted flare brake pipe.

If you tell the clerk what you're trying to do, he might help find the right parts.

It's much less complicated than it sounds. You will need to re-bleed the brakes.

All this will tell you is if that valve is causing your symptoms.
Your symptoms may be different than I think they are.
It's difficult to reach you pedal from here :)