Brakes - questions

[53lowdown]

Originally Posted by padresag

proportioning valve proportions(regulates) the flow between the front and rears brakes on a gm setup. if you didn't have one at all your back brakes would be locking up first
ron

Right - I have been adjusting the valve to diagnose this problem. From full shut, to wide open, and steps in-between. I can't get the front discs to effectively stop the truck regardless of how I have the valve set.

[Palf70Step]

What did the proportioning valve come off of? Some folks mustakingly pu on a drum brake distro block instead of a true proportion valve. Where are u getting the vacuum pull from?

[padresag]

Originally Posted by 53lowdown

Right - I have been adjusting the valve to diagnose this problem. From full shut, to wide open, and steps in-between. I can't get the front discs to effectively stop the truck regardless of how I have the valve set.

this is an aftermarket p valve that you have?
If you can still build up your pedal pressure you still have air in the system. to bleed l/rear, r/rear, r/front, l/front.
you are sure that it is disc/drum m/c
why not give us a pic of the installation. the frt and rear lines are not mixed backwards are they(this happens)
frt brake hoses usually hold the frt brakes on after you release the pedal if they are faulty
your rear brakes are adj up.
it is usally better to go with an orig type system complete the way it is intended especially in brakes and steering unless you know what it is all about or someone says put this here and it will work. funny thing is that they have never tried it themselves.
if you have a problem sometimes it is better to back to the basic system
ron

[jayoldschool]

I believe the fix will be a proper disc/drum master cylinder, combined with the correct prop valve. Followed by correct and thorough bleeding.