Rear Brakes Locking Up

[Andronikos]

so you said you checked everything 5 times, but you verified you replaced things as a parts canon and did not inspect things up close

So you are lying to us or maybe us and yourself

You needed to replace ALL the parts? To the brake pedal pad, to the drums/discs at the other end, to the booster vacuum filter and hose to the intake you REPLACED EVERY component?

please make a list of them if you did not quite literally do that
words have meaning and every single part of the system has a specific purpose, and some of them I think of would affect things you might not even realize means that you may be missing something
If you have a list on a website like amazon you could send screenshots too

Otherwise actually seeing your brakes like @CalSgt says is my vote on next thing (plus tell us what everything was)

The truck was incomplete when I bought it, and the entire brake system was, IMO, in bad shape. It didn't run when I bought it so I have no before/after reference. I have no reason to lie to anyone on this forum. I'm simply seeking insight or advice. If you have some of that please let me know, but don't call me a liar.

New: Master cylinder
Steel lines from master to prop valve
Steel lines from prop valve to each front caliper rubber line
Both front caliper rubber lines
Both calipers
Both front rotors
4 front brake pads
Steel line from prop valve to frame above differential
Rubber line from frame to the brass "T" fitting
Steel lines from "T" fitting to each rear wheel cylinder
Both rear wheel cylinders
All 4 rear brake shoes
All the rear spring, parking brake, hold down hardware
Both rear drums
The rubber pad on the brake pedal
All parking brake cables, balancer, etc

Used: Proportioning valve
Brass "t" block at rear differential
Brake booster

 

[Andronikos]

The first question was asking if the rear brakes were locking up before the work was done, did you not drive it before?

The reason for the second question was “stock replacement” could still be wrong parts, due to different options many incorrect parts can still bolt right on and sometimes even work just fine. If you still have the old parts somewhere don’t turn in your cores or toss them until you get to the bottom of the issue.

No, I did not drive it before. All the used stuff was tossed out. What parts could be "wrong" causing this?

 

[Blue Ox]

Here's a "not recommended" trick to test the front brakes. Use a vise grip VERY carefully to squeeze the rear brake hose which effectively shuts off the rear brakes. Then see if the fronts can stop the truck.

Needless to say, a lot can go wrong here, which is why it's not recommended. Too much squeeze can damage the brake line. If your front brakes really don't work your parking brake had better. The term emergency brake is a misnomer. The self energizing feature of these brakes makes them pretty much on or off. That all being said, I take no responsibility for your attempt. But I have done this successfully to diagnose a similar problem.

 

[AuroraGirl]

The truck was incomplete when I bought it, and the entire brake system was, IMO, in bad shape. It didn't run when I bought it so I have no before/after reference. I have no reason to lie to anyone on this forum. I'm simply seeking insight or advice. If you have some of that please let me know, but don't call me a liar.

New: Master cylinder
Steel lines from master to prop valve
Steel lines from prop valve to each front caliper rubber line
Both front caliper rubber lines
Both calipers
Both front rotors
4 front brake pads
Steel line from prop valve to frame above differential
Rubber line from frame to the brass "T" fitting
Steel lines from "T" fitting to each rear wheel cylinder
Both rear wheel cylinders
All 4 rear brake shoes
All the rear spring, parking brake, hold down hardware
Both rear drums
The rubber pad on the brake pedal
All parking brake cables, balancer, etc

Used: Proportioning valve
Brass "t" block at rear differential
Brake booster

lol you literally did the pad on the pedal, good guess on my part

So what im hearing is you didnt replace anything. im glad I asked.

There is supposed to be a filter on the hose to the booster, and it has to be very stiff walled booster tubing (theres a specific SAE number that corresponds to it) and a check valve on the booster.

you still refuse to send photos. Id like to see one of the previous mentioned things and the master cylinder
then go look at your front calipers, is the bleeder visible from the back? If it is, send a picture or describe where it is on the calipers. Show me a product listing for your pads as well.

Did you burnish the brakes(I think I may have asked already?)
Then, since you didnt say anything, describe how you went about lubricating your brakes and where at. use a diagram if you need to show vs explain / a picture.

in my opinion if the old lines were rusty, the brake line block on the diff should be unhooked and blown out, and the lines to the wheels removed , and blown back upstream unhooked from the block too, a lot of rust can build up in the final parts, if rusted badly the block could have a partial debris restriction.


your brake pedal pivots are worth checking, just wiggle pedal and look up from the floor, see if theres any wear that would allow the pushrod or pedal to travel in an arc instead of transmitting the pivot of the pedal to the pushrod without losing any distance like being worn would


And my statement about the lie thing is to drive home how important being exact and more descriptive of literal things taken, so thank you for describing

 

[AuroraGirl]

Here's a "not recommended" trick to test the front brakes. Use a vise grip VERY carefully to squeeze the rear brake hose which effectively shuts off the rear brakes. Then see if the fronts can stop the truck.

Needless to say, a lot can go wrong here, which is why it's not recommended. Too much squeeze can damage the brake line. If your front brakes really don't work your parking brake had better. The term emergency brake is a misnomer. The self energizing feature of these brakes makes them pretty much on or off. That all being said, I take no responsibility for your attempt. But I have done this successfully to diagnose a similar problem.

except in reverse, theres no self-energizing action in reverse
I believe some drums trade being self energizing to be directionally insensitive but require more force/fluid and so not common on american ones

 

[AuroraGirl]

?

if everything was replaced, tested, and to stock condition (the testing would verify that) it would have to work

for it not to work, means that something is missed, mixed up, or similar

 

[Ricko1966]

As someone already suggested did you look at the orientation of the rear shoes. BOB that means big on back. If you put the long shoe in the front position instead of the rear position the brakes will be extremely grabby.

 

[idahovette]

As someone already suggested did you look at the orientation of the rear shoes. BOB that means big on back. If you put the long shoe in the front position instead of the rear position the brakes will be extremely grabby.

post #48?

 

[CalSgt]

Pictures….

It’s time for pictures, perhaps we may see an issue you overlooked. I’ve had my butt kicked in the past and would be ready to quit, my dad or a buddy would glance at it and point out a simple thing I had gone blind to.

I’ll add if the RPO list is in the glove box get a picture of it too, one of the skilled guys on here can probably identify exactly what brake parts should be on your truck using that RPO list.

 

[Andronikos]

As someone already suggested did you look at the orientation of the rear shoes. BOB that means big on back. If you put the long shoe in the front position instead of the rear position the brakes will be extremely grabby.

Short on front long on back

 

[Keith Seymore]

An '86 C10 with 1" rotors and 2" shoes would be RPO JB3, and these are the parts it should have:

You must be registered for see images attach

 

[Keith Seymore]

I note that my '87 R10 has the JB5 system, which has the same front system as JB3. The differences are in the rear brake and proportioning to the rear.

My '87 stops perfectly with the original stock parts, and is the standard by which I judge other systems and setups.

K

 

[Andronikos]

Pictures….

It’s time for pictures, perhaps we may see an issue you overlooked. I’ve had my butt kicked in the past and would be ready to quit, my dad or a buddy would glance at it and point out a simple thing I had gone blind to.

I’ll add if the RPO list is in the glove box get a picture of it too, one of the skilled guys on here can probably identify exactly what brake parts should be on your truck using that RPO list.

An '86 C10 with 1" rotors and 2" shoes would be RPO JB3, and these are the parts it should have:

You must be registered for see images attach

Thanks Keith, I'll go over that information.

 

[DoubleDingo]

And post some pics of the brake system we're blindly diagnosing!

 

[Ricko1966]

post #48?

Post 40,I didn't make it to 48. I generally try to stay out of the threads that get this long,because,I don't read all 500 posts.