Proportioning Valve

[GSD Guy]

Hey everyone, I'm getting ready to swap out the MC on my 72 Blazer because the seals are going and wanted to get my ducks in a row before it's not capable of stopping. I know that the button on the front of the proportioning valve needs to be pressed during bleeding but when I took the rubber boot off of the button I was surprised to find that it already seems depressed. There is a small (about 1/8" diameter) green plastic "button" sitting inside of a round raised metal stud (about 1/2" diameter). The green "button" is sitting flush against the metal stud and can be depressed about 1/8" (therefore recessing it into the stud) with the tip of a screwdriver or something similar. This struck me as odd because there is nothing sticking out to "depress" for bleeding, so I'm not sure how the homemade tools would do anything while bleeding. This leads me to think that this is not normal. The truck seems to stop ok, minus the occasional miss by the MC. Any help would be appreciated, Thanks!

[GSD Guy]

I took a few pictures of the reset button. Is this what it should look like? The light colored metal does not move, the green center does but it already sits flush so a 90 degree bracket wouldn't do anything for this, can anyone confirm how theirs looks? Thanks

[99 to Life]

I have a different prop valve as mine is actually mounted flat not vertically. But my pin sticks out a very little bit. Your definitely looks odd. I can't say what would cause that.

[Critter]

Maybe I'm an idiot but I have never pushed that to bleed brakes in all my 20 years of bleeding brakes. I have heard of people doing it but never really knew why. The only reason I ever used that "button" was to reset the piston to a neutral position in the event that something went wrong aka a broken line, bad caliper etc. Here is a diagram just for the heck of it.

[old man jimmy]

Originally Posted by Critter

Maybe I'm an idiot but I have never pushed that to bleed brakes in all my 20 years of bleeding brakes. I have heard of people doing it but never really knew why. The only reason I ever used that "button" was to reset the piston to a neutral position in the event that something went wrong aka a broken line, bad caliper etc. Here is a diagram just for the heck of it.

I'm with you. I never use it either. Most of the time a few pumps on the pedal after the problem is fixed is all it takes to center the piston.

[Burt4x4]

Originally Posted by old man jimmy

I'm with you. I never use it either. Most of the time a few pumps on the pedal after the problem is fixed is all it takes to center the piston.

3rds ~ Mee Too, never needed to use it...even after swapping out the 1/2Ton Master/Booster too a 1Ton Master/Booster.

[1949gmc]

Is there ever a need to replace the proportioning valve?

[GSD Guy]

I bled the brakes with a pin clamped into the button to hold it down and no brake light (I know it works and isn't burned out) is on and the brakes work fine so I'm assuming that it worked haha. Stops on a dime (relatively speaking) with the new MC haha.

[99 to Life]

I thought I had proportioning valve problems, as I had all new everything and I couldn't get any fluid to my lines. I had other problems. But from what I can gather with the prop valve is, it is better to use one than not. For one, it would be nice to know when you have no brake pressure and two it will distribute fluid to one end or the other in event of a leak.

I am sure they can go bad, there are some little pieces in there. But I am pretty sure your pin should be sticking out not in.

I am far from an expert on these though.