1987 Wagoneer REAR (was front) brakes locking up

[Jeepdawg]

The title pretty much sums up the problem.

Brakes work fine but the modulation seems sensitive. Just a little bit more brake pedal pressure and I get locking.

Do these rigs have proportioning valves which can go out of adjustment, or fail?

I could start throwing parts at the problem but I would prefer to start that process with the likely culprit.

[joe]

Yeah they have a NON adjustable prop valve but that's not your problem. I'd guess your pucks/calipers are toast. AKA time to pony up and rebuild your front brakes.

[serehill]

well

If you've bled them recently & didn't reset the PPPV it might do this. You might take a look at the PPV & see if you need to reset it.

[Jeepdawg]

Nope, did not bleed the system recently. Is the pppv the proportioning valve?

I did not know it had a provision to reset it. I'll take a look.

[davidpsalt]

Am assuming you are talking about your front brakes - my bet is that your front caliper on one or the other side is locking up - rust on the piston is typically the reason. Very cheap fix if you can do it yourself. I have a 1989 and this was my problem - I bought new calipers for both sides - only about $15 each from Napa - also bought new pads ($35)and new brake hoses ($30). Rotors were fine. Fun job two. by doing all of this I eliminated any concerns with my front brakes. At some point the rotors will need to be done but I will wait until I get the shudder when braking and then tackle that job. The rotors are attached to the hubs - never done this on a wagoneer but I will plan on repacking wheel bearings etc at the same time.

[Jeepdawg]

I did some reading on the proportioning valve. From what I understood, the valve only comes into play under severe braking. Under normal braking the MC sends pressurized hydraulic fluid under directly to the brakes through 3 lines, 2 to the front and 1 to the rear.

So I think I agree, it's probably a sticky caliper. The valve does not seem to be a factor in the system under normal braking.

The calipers are cheap, although the worst part of the job is bleeding the system.

Since I have to bleed it , I am going to replace the MC and hoses too. At least I have a somewhat reasoned plan together before I start throwing parts at it.

Thanks!

[serehill]

Yeah it's just somethuing to check firt

It could very we'll be a caliper issue. Even though the PPV ( yes proportioning valve) is not adjustable it can lock into position. Flow can cause it to lock in one position or another. It could remove pressure on the rear shoes which will cause the front to do all the braking. It doesn't have to be adjustable to do that. If it does then the front brakes tend to lock up from doing all the work. If both calipers are locking up balanced this becomes a possibility. New calipers are cheap though. If one wheel is locking up then it's not a PPV.

Good info:

http://www.reddingwheelandbrake.com/brakesafety.htm

[Carnuck]

Sometimes it's the hose swollen inside too.

[Jeepdawg]

I installed new front calipers and pads today and it didn't help.

The problem seems to be the right rear wheel locking up.

Could it be the master cylinder?

Any ideas?

[Tripwire]

I agree with Carnucks idea also, the rubber hoses swell up inside and can act as one way check valves.....replace them at the same time you change the calipers

[Carnuck]

Right rear means dump the dust out of the drum. Look for cracks or hot spots or any weeping oil.

[Jeepdawg]

'87 GW Rear brakes locking up

I changed the title, it was actually the rear brakes locking not the front. (DOH!)

Definitely not swollen brake lines. When I unbolted the rubber lines from the calipers, brake fluid drained freely out the lines, and when I bled them I had plenty of fluid flowing. In the back its a steel line not rubber, although there is one rubber line that feeds both cylinders on the rear axle.

Looks like I will be ripping into the rear wheels and replacing the wheel cylinders next.

[Mikeswagon]

mine did that too - easy answer, get the shoes on right! I could´t tell there is a difference in primary and secondary shoe, but there is.

Try change them.....

[Jeepdawg]

It's possible the rear shoes are mixed up, although I have not touched the rear brakes. Maybe the PO messed that up.

He screwed up the Howell EFI when he installed it.

Wheel cylinders and shoes are cheap and in stock. Plain 'ol chevy parts.

[Jeepdawg]

OK, wrapping this up.

I replaced the front calipers and pads, no change. back to Napa auto parts.

Picked up two new rear wheel cylinders, shoes and a master cylinder.

When I took the rear drums off, I noticed it right away. No leaking, nice and dry.

But....big shoes in the back on one side, and on the front on the other side. DSPO put the shoes on backwards on one side.

So I installed the new master cylinder, wheel cylinders and shoes, big on back, BOTH sides this time.

Brakes work awesome now. Nice and steady pressure no locking up.

It was definitely not the proportioning valve.