Need help with prop valve

[68jimmy]

This disc brake upgrade is getting to be more of a pain the a#$ than it's worth... Anyway to the real issue. I have swapped the master cylinder/booster/prop valve from a 72 c-10 parts truck to mine. During the bleeding it seemed that the master cylinder was not working to the rear brakes. Yesterday I purchased a new master cylinder, bench bled it prior to install. Installed itm attached all of the hard lines and started the bleed process.
Front brakes, no problem. Get to the rears and I'm just getting a trickle... So I recheck all the lines and connections still the same results. So I start with the troubleshooting guide at cpp.
http://www.classicperform.com/TechBo...tm#tshootbleed

While testing the prop valve with a test light I find that it lights up. So I remove the switch from the prop valve and discover that the internal valve is towards the rear. So I take a small screwdriver and puch it forward, re-install the switch and check with a test light. All seems good. In following the guide it recommends that I open the bleeder valves on the wheels that are working ok, in this case the fronts. I do so and gently push the brake pedal all the way to the floor a couple of times. When I recheck with the test light it is grounded again! I remove the switch again and the valve is towrds tha rear once more.

Do I need to get a new prop valve? Is there any other tips or tricks I should try? Help!!

Thanks in advance....

[c-1072]

i just installed a used booster master cylinder and prop valve . fronts bled out no trouble . rears nothing after pulling apart the prop valve tried it again no good . I had a old prop valve from my blazer swapped it out and it worked great . thats just what happend today hope it helps .

[68jimmy]

Well I got it to work finally... Here is how:

1. Removed the switch from the prop valve and re-centered the valve. Re-installed the switch.

2.Re-bled the brakes but this time I did the gravity method, starting with the rears on the right side.

3. After the bleed the pumped the brake pedal a few times and let it set. Meanwhile I re-checked the switch with the test light, no light all is good.

4. Re-bled the brakes once more, gravity method once again.

5. Cleaned up and took it for a spin!

[HUEVUDO]

what kit , and how much, and how much time was needed to do it?

[68jimmy]

Not a kit but more a gathering of parts... I followed the disc brake swap from the faq:
http://67-72chevytrucks.com/vboard/s...ad.php?t=35042

I used parts from my 68 a 72 and a 90....

[qksilver]

What happens is that the valve gets moved father than usual and it sticks. Sometimes when people bleed used M/C instead of gently pumping the pedal and not going all the way to the floor they pump it hard all the way to the floor and either the prop valve or master cyclinder will stick. Gravity bleeding generally works best with used parts.

[68jimmy]

Originally Posted by qksilver

What happens is that the valve gets moved father than usual and it sticks. Sometimes when people bleed used M/C instead of gently pumping the pedal and not going all the way to the floor they pump it hard all the way to the floor and either the prop valve or master cyclinder will stick. Gravity bleeding generally works best with used parts.

That is exactly what I discovered during my trial and error brake bleeding adventure... It was certainly worth it though the disc brakes up front sure do feel much better than the previous drums...