Prop Valve Question

[tex_waco_usmc]

I think my prop valve is a no go. Every time I get into the 87 it seems that initially I am dragging the right rear tire when I step on the brakes. When I bled the brakes it was almost impossible to get brake fluid to the rear brakes. I think the prop valve has given up. Problem is I cant seem to find a replacement at the parts store. Anyone have a part number for a prop valve?

[geezer#99]

You might have a leaky wheel cylinder or fluid on your shoes.
Did you hold the reset pin in in the end of the prop valve when you bled the brakes?

[tex_waco_usmc]

Originally Posted by geezer#99

You might have a leaky wheel cylinder or fluid on your shoes.
Did you hold the reset pin in in the end of the prop valve when you bled the brakes?

I replaced the wheel cylinders and have checked the wheels for leaks and haven't seen any signs of leakage.
Yeah we held it, but it didn't feel like it was moving at all. (Part of the reason I think it is seized)...

[Keith Seymore]

For what series or brake option?

Brake system release charts for an '87 pickup/utility attached below:













Prop valve is labeled as "comb valve asm" (aka "combination valve").

K

[tex_waco_usmc]

It is a 2WD 1/2ton SWB with the 350 TBI/700 R4...

[Keith Seymore]

Originally Posted by tex_waco_usmc

It is a 2WD 1/2ton SWB with the 350 TBI/700 R4...

I'd go with the 18008085, for the JB5 brake system with a 6100 lb GVW.

K

[tex_waco_usmc]

Originally Posted by Keith Seymore

I'd go with the 18008085, for the JB5 brake system with a 6100 lb GVW.

K

Again man you have helped me out tremendously! Thanks Brother! Going to order it today and when I return from this business trip I am going to get the truck closer to the ground and brakes working properly!

[Oldriginal86]

My 86 k2500 would do that even after rebuilding the rear brakes. Found it was the Ebrake cables were rusted. Replaced cables and never he'd the issue again.

[mrolds88]

What about the adjusters? Might have one stuck or one adjusted tighter than the other.

[Tx Firefighter]

Originally Posted by tex_waco_usmc

I think my prop valve is a no go. Every time I get into the 87 it seems that initially I am dragging the right rear tire when I step on the brakes. When I bled the brakes it was almost impossible to get brake fluid to the rear brakes. I think the prop valve has given up. Problem is I cant seem to find a replacement at the parts store. Anyone have a part number for a prop valve?

You're describing what happens when you have a bad rear brake hose.

-dragging brakes
-hard to get fluid out when bleeding

I'm just saying, the hose is rubber and likely old and they absolutely do swell shut inside. I've changed the brake hoses on two 73-87 trucks this year already for the same reasons. When you take them off, you can't blow through them. They look good on the outside but swell shut internally from long term exposure to the brake fluid. You can horse down on the brake pedal and push fluid through them under pressure, but once released, the fluid is not under enough pressure to push back through the clogged hose, hence they drag.

New hoses are less than 10 dollars each from Rockauto.

Look at it this way, if you invest 30 dollars into new hoses and it doesn't fix the problem, you haven't really wasted any money, as 25 year old hoses aren't really a good idea on your braking systems anyway. Then, if you still have problems, you might look at a new combination valve which is significantly more expensive than hoses.

[tex_waco_usmc]

Originally Posted by Tx Firefighter

You're describing what happens when you have a bad rear brake hose.

-dragging brakes
-hard to get fluid out when bleeding

I'm just saying, the hose is rubber and likely old and they absolutely do swell shut inside. I've changed the brake hoses on two 73-87 trucks this year already for the same reasons. When you take them off, you can't blow through them. They look good on the outside but swell shut internally from long term exposure to the brake fluid. You can horse down on the brake pedal and push fluid through them under pressure, but once released, the fluid is not under enough pressure to push back through the clogged hose, hence they drag.

New hoses are less than 10 dollars each from Rockauto.

Look at it this way, if you invest 30 dollars into new hoses and it doesn't fix the problem, you haven't really wasted any money, as 25 year old hoses aren't really a good idea on your braking systems anyway. Then, if you still have problems, you might look at a new combination valve which is significantly more expensive than hoses.

Oh how right you are! I thought about that but it doesn't drag after I release the pedal it drags when I barely touch the pedal! LOL As soon as I release the pedal the wheel frees and is good again. But no matter how long or hard I bled the brakes, no matter how we did it the right rear wheel seems to be getting all the pressure. Yes, I know it doesn't make any sense as the two rear wheels are fed by the same line. I've still got some investigating to do on why only one of them is locking, but I cant seem to get the front brakes to do what they are supposed to do and that is what leans me towards the combo valve!

When I get home I am going to take the bed off of the truck and clean and paint the rear half of the truck like I did the front half, as well as do a flip kit on the rear axle. I was planning on replacing all of the rubber lines and I am going to replace the prop/combo valve at that same time. At this point I am just collecting parts for this job.