Touchy Brakes- lock up

[2badgn]

I have a 1984 GMC Sierra 3500 2x4 single rear wheels. Last year, I had my Chevy dealer replace the brakes. They cut the drums & replaced the shoes. They also changed both front discs, calipers, brake pads and brake hoses.
Master Cylinder was also changed.

My dad and I usually drive around town but this weekend i took the truck on the highway.

The brakes are touchy. Sometimes they lock up. When on the highway & I apply the brakes, there is some vibration but then it will go away.

I was parking the truck and as I was reversing very slowly, 1 of the tires skidded. Sometmes when driving, it seems as if 1 of the wheels isnt catching when the brakes are applied & the truck will hop or bounce or sink- Its tough to describe. Front end sinks to right slighlty.

Im going to have the mechanic check it out but wanted to know for myself, what could be the problem.

[turner16]

I had a rear seal go in my 25 and it caused the breaks to grab. Just that one wheel.

[78 Chevyrado]

Originally Posted by turner16

I had a rear seal go in my 25 and it caused the breaks to grab. Just that one wheel.

I'm having that problem right now with my 3/4 ton. I've done everything and the inner wheel seal still leaks so I'm going to buy a sleeve kit for the axle tube and try that.

[3r!c84]

Originally Posted by 78 Chevyrado

I'm having that problem right now with my 3/4 ton. I've done everything and the inner wheel seal still leaks so I'm going to buy a sleeve kit for the axle tube and try that.

wouldnt leaking gear oil on one side make it pull the other way becuse the oil soaked drum is not grabing there for the other side is doing all the work.

but this dont enplane locking up

[topever]

I have the same problem with my 3/4 ton 4x4. Full floater 14 bolt. right rear locks up. replaced seal twice, seal saver, still does it. I'm thinking that the gear oil is turning to sticky gum on the shoes, which makes it grab like that. If I run down the road power brakeing it, it seems to heat up enough to behave for a while. CRC'd shoes and drum real good. lasts for a little longer,but really getting to be a pain. What am I missing here? One guy told me the rear bearings need to be set with a pre-load. Just does'nt make sense, the drum isn't moving around any to cause the seal to leak. I have heard more than one story identical to this. Does anyone have an answer?

[jablack]

I would check to see if the shoes were put on right. I bought a rear end that had new brakes but the rear shoes were on one side and the front shoes on the other.

[nerphin]

interested in this thread. my 3/4 ton locks up pretty bad when i first pull out of the garage. no leaks or anything that i can see, and the brakes were done right before i got it.

it goes away after the first few good stops from speed.

[Cue-Ball]

Originally Posted by 3r!c84

wouldnt leaking gear oil on one side make it pull the other way becuse the oil soaked drum is not grabing there for the other side is doing all the work.

but this dont enplane locking up

Oil on brakes doesn't act the same way as it does between two metal surfaces. The oil makes the brake lining material sticky, and it also makes it swell. So, not only does the brake have a tendency to lock up more easily, but it also ends up grabbing before the opposite side does because the pads are swollen.

[turner16]

you did replace the shoes after the seal went right? I have replaced my seal 2 times in 7 years. Must be a design problem?

[DetroitDan]

I have the same problem with my left rear fullfloater, I replaced the seal and brakes, then the seal again and cleaned the brakes, I think something is bent a hair and the seal wont seal. Now what I do is drag the brakes a little when I first start driving it, goes right away. About once a year I have to top off the rearend. And oh yeah, the left rear simulator is always oily and dirty, have to clean it more than the other three. I'm done pulling it apart and messing with it.

[tucsonjwt]

On my 83 C20 I had brakes grabbing due to rear wheel seal (aka axle seal) leak.
GM now makes a two piece, rather than a one piece, rear wheel seal. It is like the inner/outer race of a bearing - one part moves while the other part is stationary. Leaking seals is a known defective design for the GM floating axles, which is why GM came out with the two piece seal. I don't remember the GM part number, but is is only available from GM. IMO, GM should have done a recall on this, but no such luck. My drivetrain guy replaced my seals twice, before I researched the internet and came up with this answer. It is strange to me but GM still sells both old one piece and new two piece seals.
On a side note, my brakes locked again last night, but it was due to driving through flooded areas and soaking the drums in deep water.

[Eyegore]

I may have missed it but i did not catch anyone mention having their rotors or drums turned. If you are having vibration this could be part of the problem, when they get hot they warp or cracked, turning them within tolerance keeps this from happening. I spoke to a mechanic who said that he had new rotors turned since they sometimes warp sitting on the shelves.
As to rear brakes catching and locking up why not get an adjusting tool and back off the shoes from the drum?

[Adams74Chevy]

Also it could be the wheel cylinder, I've had that happen it only took 30 years or so for the original one to go bad...needless to say they are cheap enough I replaced both when the one went out.