Brake Issues - 85 K20

[Moloko]

So I bought this 85 K20 back in June that was left at a local shop due to it's brake lines rusting out. I replaced the master which was leaking, all the brake lines, rear wheel cylinders, and front calipers. After I bleed the brakes (both normal, and with a Phoenix reverse bleeder) It has pedal when the truck is off, and will pump up and hold pressure. When I turn the truck on the pedal goes right to the floor, and the prop valve trips to the front. I went as far as to re-change the rear brake line again tonight thinking it was leaking at the junctions, and it still trips the valve the second you touch the brake pedal.

Could the prop valve be bad? I've never heard of it, I've only heard of people changing them when they won't re-center after tripping, but I've been taking it off and manually pushing it back with a pick each time.

[86c20]

last time i had that it was the rear wheel cylimders. and that was on a 86 c20 with the heavy breaks

[Moloko]

Bad as in leaking? Because I changed them, and it had this problem before and after changing them.

[geezer#99]

Did you keep the reset pin held in while you bled the brakes?

[donut]

x2, and if you have power brakes, unplug and cap the vacuum the booster, see if it still does it.

[Moloko]

Originally Posted by geezer#99

Did you keep the reset pin held in while you bled the brakes?

No, I reverse bled them from the wheels in.

[geezer#99]

Originally Posted by Moloko

No, I reverse bled them from the wheels in.

Could you take the time to explain 'reverse bled'?

[Moloko]

I have a Phoenix reverse bleeder. It has a pump that pushes the fluid from the bleeder screws at the wheels back up to the master. It pushes all the air out infront of the fluid.
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[86c20]

try adjusting them way up that was the only otherthing that i ran into. and i mean way up

[geezer#99]

Originally Posted by Moloko

I have a Phoenix reverse bleeder. It has a pump that pushes the fluid from the bleeder screws at the wheels back up to the master. It pushes all the air out infront of the fluid.
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Thanks!
Your prop valve likely has a residual check valve for the rear brakes.
Do you get air bubbles in the m/c on the rear brake side?

[Moloko]

No, no air bubbles from any wheels.
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[Moloko]

Would this pressure valve cause the issues? I did notice a series of rubber diaphrams inside the prop valve when I took it apart.
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[geezer#99]

You should of got bubbles back into the master. Air has to go somewhere. Even while bench bleeding the master you get air bubbles up from the piston return hole.
Maybe you need to depress the pin on the prop valve, lock it down and rebleed the system the conventional way. From the master to the furthest cylinder and back to the master.

[Moloko]

No I mean it no longer has bubbles when I bleed it, all the air is out of the system
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[ozbowhunter]

What reset pin ????

[ozbowhunter]

will this fix my brake light problem on the dash ?the reset pin when I bleed the brakes (sorry not trying to hijack the post)

[Moloko]

There is a button on the driver side of the valve, but from what I can tell it will only reset if the valve has tripped to the rear (blocking off the front brakes). I don't see how it will do anything for the valve tripping to block the rear brakes.

[Moloko]

Update, I put on another used prop valve, and after about 5 minutes of bleeding the brakes were fine. This has been fixed for two weeks or so, just havn't gotten around to updating everyone.