proportioning valve issues?

[jonathan-m]

Hi guys,
Hopefully someone can point me in the right direction here because I'm about at the end of my rope.
I started having a bunch of break issues a while back, such that I finally had to break down and buy a new car and retire my truck as a DD because I couldn't get it worked out. I parked the truck for about 6 months to let the frustration die down, but now I'm back at it (and quickly building the frustration back up)

Here's the lowdown:
front disc, rear drum.
I've replaced the brake booster (the initial issue, which in turn has spawned the current issues)
replaced rear drum cylinders,
inspected all soft and hard lines for leaks
replaced the master cylinder (today)

The issue that I had after installing the new brake booster was that the front brakes would completely lock up. I found this out the hard way after getting about eleven miles down the interstate headed for work before smoke started coming out from the front wheels and I ended up pulling her over and having it towed home (the day I decided to retire her...)

My thought at the time was that the pushrod inside the new booster might be the wrong size for the MC that was still being used from the old booster, so just in case I bought a new MC to match the exact booster I had purchased.

I installed the new MC today (after bench bleeding it). Now the issue I'm running into is that I'm unable to bleed the system properly, I'm getting no solid flow of fluid from the rear lines when I try to bleed them (I tried both a vacuum bleeder and manually), and even with the correct MC and BB combination my front discs still completely lock up and don't release.

After a little more research (and damn near 2 full wasted days of tinkering), I've decided that maybe the issue has to do with the proportioning valve which apart from the hard lines is the only part of the system that I haven't replaced.
Unfortunately mine was annoyingly positioned directly under the radiator fan and is quite hard to access. I'm also not entirely sure how to adjust this thing, and even after doing some reading online I'm not sure how to adjust this one (or if the Prop valve is even the likely culprit here).



Anyway, sorry for the long winded rant-- I'm clearly out of options, and can't even drive the truck far enough to get professional help, so I'm really hoping you guys can help me get on the right track with this.


Thanks,

Jon

[geezer#99]

Did you push and hold in the reset pin in on the end od the prop valve?

[jonathan-m]

I haven't done anything to it as of yet. I took a good look at it this evening, but I didn't see a pin on the end. I'll have a look at that tomorrow morning. Is there anything else I should be looking to do to the prop valve besides a reset?


Thanks,
Jon

[geezer#99]

The pin should be on the left side in your pic. On the end under a rubber cap. Here's a link from cpp to trouble shoot your brakes.
http://www.classicperform.com/TechBo...t.htm#testprop

[jonathan-m]

Originally Posted by geezer#99

The pin should be on the left side in your pic. On the end under a rubber cap. Here's a link from cpp to trouble shoot your brakes.
http://www.classicperform.com/TechBo...t.htm#testprop

Thanks for the link, I'll have a good look at that tonight before I try again tomorrow.

[TR65]

Jonathan,

It sound like the push rod from the pedal was not adjusted correctly. If the push rod doesn't allow the piston to fully retract then the pressure won't release and eventually the brakes will lock. There should be clearance between the rod and the piston with foot off the brake.

Just a thought.

Good luck,

TR