Mystery of the irrepairable drum brake pulsing

[@dam]

If I do an axle swap, how do I know if the Liberty (or Grand Cherokee?) I take it from has the same gearing?

How do I evaluate the quality of drums?

 

[heyhar]

Uh, you're not taking the whole axle, just the backing plates and other stuff relating to the brakes. Both the grand and Libby have coil springs, so unless you have mad fabbing skills, keep your buggy springs.

 

[WrenchMonkey]

With your rig pushing 200K, how old, or how many miles on the drums?

Have you read the thread? Replaced more than once...

Uh, you're not taking the whole axle, just the backing plates and other stuff relating to the brakes...

I'm sure 90X meant to swap in another XJ axle...

Robert

 

[Ecomike]

I talked to a manager at Autozone tonight, and she confirmed there have been problems with bad brake parts off the shelf (CHINA). She mentioned her husband having similar problems......

She said they only have one brand, (Duralast) so I would try a dealer (but they may be too pricey), or try NAPA for a good brand of drums. You might get lucky at JY and find almost new, good drums.

I would also replace the equalizer valve first!!!!!! It could be defective, and could be the real problem. You should be able to check the brake backing plate visually for flatness with the brake shoes mounted. If the backing plate is not flat and parallel it will rub on the brake drum and will be quite obvious!!!!

 

[techno1154]

The more I think about it the more I am convinced that your problem are not a bent axle or break backing plate. Either of them would bind wether or they are hot or cold. Think about it,...a rotating piece of steel would wobble all the time no matter what. I would instead focus my efforts on the break drum, break shoes and/or the break hydralic system like the combination valve not allowing the fluid to return fast enough although I do not know if it is possible.
You also said after a major break job that things settle for a while until some miles are put on the replaced parts. Maybe and just maybe the replacement shoes get sticky after some surface wear.
Let us know what work for you.

 

[Ecomike]

The more I think about it the more I am convinced that your problem are not a bent axle or break backing plate. Either of them would bind wether or they are hot or cold. Think about it,...a rotating piece of steel would wobble all the time no matter what. I would instead focus my efforts on the break drum, break shoes and/or the break hydralic system like the combination valve not allowing the fluid to return fast enough although I do not know if it is possible.
You also said after a major break job that things settle for a while until some miles are put on the replaced parts. Maybe and just maybe the replacement shoes get sticky after some surface wear.
Let us know what work for you.

I agree. The more we discuss it, the more the combination valve (I call it an equalizer valve), sounds like the likely suspect, perhaps acting as a one way valve and not relieving pressure on the rear once the Jeep is stopped, and / or sending all the work to the rear brakes instead of spreading of the load properly.

 

[heyhar]

Come to think of it, when I replaced the rear hard and soft lines on my '92, the rears began behaving fine. I posted earlier about the clunking, and you could feel a pulse/grab at each clunk, and I'd forgotten that it seemed to disappear when I did the lines. I'm about to put new shoes on the rear for state inspection, and I hope I don't upset the balance of the universe!

Mike, I think your idea about the fluid becoming trapped is probably right on target. That, and the crappy East Asian drums, that warp on a sunny day...

 

[@dam]

How do you think the lines fixed it, heyhar? It seems like a line would make it drag all the time- not once per rev and only when warm.

 

[WrenchMonkey]

How do you think the lines fixed it, heyhar? It seems like a line would make it drag all the time- not once per rev and only when warm.

If the line held pressure in the cylinder, it could make the shoes drag, which could heat up and warp the drum...

Could be!

Robert

 

[heyhar]

I'll guess Mr. Wrench hit it on the head. Obviously, I could be completely wrong, but the symptoms disappeared when the lines, both hard and soft flex from the body to the axle were replaced. I also replaced them on my '96, and although it wasn't acting up, the operation of the brakes improved noticeably. I will say that where I live, Northeast PA, is not kind to cars and the various steel lines underneath. Right now, I'm doing inner and outer rocker panels and repairing the floor pans on my '96. Got Rust?

 

[@dam]

zero rust on my car, and great mpg, so I doubt I'd have dragging. Is there anyway I could check that without throwing a bunch of parts at the car? I HATE working with brake fluid.

I was thinking...a backing plate shouldn't make a once-per-rev rub. It has to be a rotating part that's out-of-wack for that to happen. A bent stationary part would create a constant problem.

 

[WrenchMonkey]

great mpg, so I doubt I'd have dragging...

I bet it wouldn't take a whole lot of drag to create enough heat to warp a drum, especially a chinese potmetal drum, extra-specially since you said it doesn't do it right away, only after it "warms up."

Robert

 

[Ecomike]

I bet it wouldn't take a whole lot of drag to create enough heat to warp a drum, especially a chinese potmetal drum, extra-specially since you said it doesn't do it right away, only after it "warms up."

Robert

I have to agree with that. Also, it would not warp the drums while rotating, only after it got too hot for the junk metal to hold its shape, and then it would only warp with brakes applied, and stopped at a light long enough for the drum to cool, while the two pads pushed out at two constant spots and warped it while it cooled. That leaves out the combination/equalizer valve as well.

BUT, bad rubber lines (bad on the inside) or bad metal lines, or a bad combination/equalizer valve might cause (or contribute to) the pulsing, in other words we may be making a mistake assume the pulsing is only caused by warped drums??? (or not?).

Has the OP tried a different brand of drums yet?

 

[Ecomike]

zero rust on my car, and great mpg, so I doubt I'd have dragging. Is there anyway I could check that without throwing a bunch of parts at the car? I HATE working with brake fluid.

I was thinking...a backing plate shouldn't make a once-per-rev rub. It has to be a rotating part that's out-of-wack for that to happen. A bent stationary part would create a constant problem.

A bent shaft and a bent backing plate, can cause a once per revolution rub!!!

 

[ZZZeDDD]

Gday mates.
Had a mid 80s cj7.
360 ci
Mid rise edelbrock
4 barrel
Herman headers accel ing
Hayes street strip
T4a tran.
Blew two rear axles and many u Jr's
I miss her.
It's a jeep thing most don't understand

The pulsing drum thing.
97 gmail safari
Same crap.
Fresh drums shoes graphite where needed
Properly set.
Still working on it as well.

Shout out to jeepers