Mystery of the irrepairable drum brake pulsing

[@dam]

My rear brakes had been pulsing for a long time, and gradually were getting worse. It wasn't a pulsation in the pedal, but in the braking force. Every revolution, braking force would spike a little. This made the rear wheels lock up very easily.

I hate working on drums, and wasn't sure of the cause, so took it to a $99 brake place. They did all four brakes, including new shoes and springs/hardware in back, and turned the drums.

It was OK for a while, and the pulsing quickly got worse. It got so bad that it started pulsing WITHOUT EVEN TOUCHGING THE BRAKES! The brake would drag once per rev and toss my head forward a little. I took it back, and got new shoes, and the drums turned again. Ran into the same problem (although it mostly only happened when I was using the brakes). New shoes AGAIN. Same cycle. Finally, I had them replace the wheel cylinders and drums. It was pretty smooth for about 800 miles. Then I had them tighten up the parking brake so it would be useable, and the problem is gradually coming back (~1200 miles now). It isn't very noticable when they're cold, and becomes more noticable after the brakes warm up a bit. Fortunately, it's no worse than it was the very first time I brought it in, so at least I'm back to square one.

I bought the cylinders and drums from the brake place because I didn't want them to blame a part they didn't install. A few weeks ago, I thought it might be inconsistently bedded-in brakes, so I did 5 hard stops from about 55. Didn't really help or hurt anything.

So, what could be causing this? The brake place obviously doesn't know how to do anything besides throw parts at the problem, but after new cylinders, hardware, shoes, and drums (oh- and axle seals, too), there's nothing left to replace back there.

Oh yeah- '95 Sport 4x4 5-spd, no ABS.

 

[kcjeep6]

Check the front rotors for runout.

 

[joe_peters]

Hmmm....

I would like to have seen the rear shoes to determine the contact surface.

Back in the good old days, before pantyhose and plastic soda bottles, to get a decent drivable set of brakes--that would be drums on all four wheels--you had to "arc" the brake shoes to make sure there was maximum contact between the entire shoe surface and the drum.

If you Google "arcing brake shoes" you can read all about it.

If you see comments like "controversial because it reduced the shoe material" that is HS from someone that never worked on all-drum brake vehicles.

Today, locating a brake shop with an arcing machine is getting difficult as disc fronts provide the majority of the braking effort and there aren't a lot of people out there that have a clue what a good brake job feels like.

 

[RCP Phx]

From your description and subsequent repairs,I'd be checking for a bent axle.

 

[@dam]

How do I check for a bent axle? If it was a bent axle, it seems like it wouldn't be better for a while after new shoes, and seems like it wouldn't be temperature dependent. Would it be the internal half-shaft, or the entire axle housing?

This car is pretty much a highway queen- just a very little light off-roading.

 

[TRCM]

Also check and make sure your ebrake cable isn't hitting a wheel weight or the DS and being tugged, thus giving you the surge.

I had this happen on my 88 when the ebrake cable was hitting a wheel weight, but it does sound like a bent axle flange to me.

 

[wreams]

To check for a bent axle, first jack up the rear, put the jeep in drive then get out and watch the brake drum. If its bent you'll see the drum moving back and forth. Be careful about running your xj with the wheels off the ground, chock the front wheels while doing this. Bent axles are more common then you would think, Ive done plenty of them.

 

[@dam]

So, I assume I have to do that with the wheel on, to keep the brake drum up tight? Are they difficult/expensive to replace?

 

[87manche]

Do you apply the parking brake with great force?

My wife's Camry would always do the same thing, and then I adjusted the e- brake so that it would barely work. She pulled on the e-brake handle so hard it would warp the drums.

 

[@dam]

I just got my tires balanced. While on the lift, we started it up. There's no noticable wobble or bend in the flange. The guy at the shop says if the new drums were stored vertically instead of flat, for an extended period, they may've warped. He says I should go back and ask for new shoes AND drums! Can that happen?

Also, anyone else hear of the parking brake causing this? It never caused a problem the first 7 or 8 years I had this truck, nor any of my others.

 

[87manche]

I just got my tires balanced. While on the lift, we started it up. There's no noticable wobble or bend in the flange. The guy at the shop says if the new drums were stored vertically instead of flat, for an extended period, they may've warped. He says I should go back and ask for new shoes AND drums! Can that happen?

Also, anyone else hear of the parking brake causing this? It never caused a problem the first 7 or 8 years I had this truck, nor any of my others.

Yes, there's big words on the boxes of rotors/drums that state store flat.

that parking brake thing is a long shot, but that's really what it was on a Camry. It's caused by applying the parking brake hard on hot drums. XJ drums are quite a bit thicker, but it's a possibility.

 

[joe_peters]

Yes, there's big words on the boxes of rotors/drums that state store flat.

that parking brake thing is a long shot, but that's really what it was on a Camry. It's caused by applying the parking brake hard on hot drums. XJ drums are quite a bit thicker, but it's a possibility.

Talked to a buddy in the Bay Area tonight--they see a lot of it in SF.

 

[@dam]

Hi guys. It's pulsing pretty bad again. It usually doesn't do it very bad when cold, but being hot it's hit or miss, too. Last weekend, after a high-speed 25 mile stretch without braking, I stopped at a light and the brake force pulsed pretty violently. The next stop...much less severe. Weird.

I took it to the brake place again. Like I've said- they've replaced everything but the lines and master cylinder. I thought no-way would either of those be the culprit, but they said it could be the cylinder. He said if the seal for the front-brake portion of they cylinder isn't holding pressure, the rear brakes would have to work too hard to compensate, and will eventually warp. They have been locking up pretty easy. I thought it was just due to the pressure-spike due to the pulsation, but maybe this is the cause. This would also explain why it usually works fine for a while after they due to shoes and turn the drums.

So...make sense, or BS? I've gone this far, so I'll have them due the cylinder too if that's what they come back with- that way they can't blame it on some part that I or someone else replaced. So I don't get screwed though, what is a reasonable price for this job?



Oh yeah...one other thing- I get a vibration between 75 and 80 mph since they did the drums. I balanced the tires twice with no improvement. Related? Ideas?

 

[orange]

--long shots--

-Perhaps the brakes are OK, but the suspension is bad??

-might check springs, shackles, bushings, etc. etc.

-Axle lube have metal traces?

Good Luck,
Orange

 

[@dam]

Well, they didn't do the master cylinder. They ordered 3 sets of drums, and they were all out of true, straight out of the box. Seems having an older car means you're likely to get parts that have been sitting for some time.

Hopefully getting some good drums will solve it, but we'll see.

 

[Ecomike]

Well, they didn't do the master cylinder. They ordered 3 sets of drums, and they were all out of true, straight out of the box. Seems having an older car means you're likely to get parts that have been sitting for some time.

Hopefully getting some good drums will solve it, but we'll see.

I ran into drum problems from Autozone last year (89 Cherokee). Right out of the box, the machine work was visually an obvious POS! No way it got through any real visual quality control inspection process. Somebody was shipping them real junk from China! A five year old could see the problem. The brake surface wall varied from 1/8" to 3/8" thick, it was that far out of being round and true! It was way off center when it was machined at the factory. Pulled 3 off the shelf before they found a good one.

 

[joe_peters]

I ran into drum problems from Autozone last year (89 Cherokee). Right out of the box, the machine work was visually an obvious POS! No way it got through any real visual quality control inspection process. Somebody was shipping them real junk from China! A five year old could see the problem. The brake surface wall varied from 1/8" to 3/8" thick, it was that far out of being round and true! It was way off center when it was machined at the factory. Pulled 3 off the shelf before they found a good one.

Try a different vendor--hint, hint. :cheers:

I honestly can't remember the last time I set foot in a Schucks/O'reilly/Autozone/whatever parts store.

 

[KD3NE_]

Also check and make sure your ebrake cable isn't hitting a wheel weight or the DS and being tugged, thus giving you the surge.

I had this happen on my 88 when the ebrake cable was hitting a wheel weight, but it does sound like a bent axle flange to me.

I had a similar issue on another vehicle. Odd pulsing of the back brakes. I found a plastic insert in an ebrake cable support had self destructed allowing the cable to vibrate and thus pulse the brake.

 

[@dam]

OK- so I took the Jeep back Friday morning. I get a call at 3:30 saying "uuhhhhh....3 of our guys drove it and don't notice a problem". I stop by after work, drive it with the manager. The pulsing is blatently obvious, and is most prevelent just before a complete stop. He starts making all kinds of excuses...how it should get worse at high speeds, etc. and telling me the drums are fine (remember- the tech who put the drums on a few days before said they were a few thousandths off WHEN HE PUT THEM ON).

So, after much needless argument, they kept the car over the weekend "but just this once more". New drums, and inspected everything. They said the e-brake looks fine. I got the car back yesterday. It's much improved (as it usually is for a short time when I pick it up). However, I still feel the pulsing very faintly. I'm so used to it I know just what to look for, but I think if a stranger drove it it would be unnoticable. Only a matter of time until it gets worse.

I also notice when driving around in 5th, I hear a very faint, rhymethic "wha wha wha"....just a slight variation in the typical background noise about once per revolution. It might be related, but I've no idea what it might be. This isn't new- been doing this a while, but this is the first time I've paid attention to it with new drums. Haven't had time to get it up to 75 yet.

The last time I had the tires balanced, I had them 'drive it' while on the lift. There was no obvious wobble in the back tires.

I'll check for any strange supports in the e-brake cable. Wouldn't I feel that in the handle as I drive though? And, wouldn't that not be noticable at very low speeds, where this problem is most noticable?

I'm about out of ideas. Getting kind of tempted to sell this thing again. This is a spare car that only gets about 5k per year, so I don't want to spend too much time on it. I'd rather fix it, but it seems like I'm chasing ghosts and not getting anywhere.

That's why I eventually took it to the brake shop in the first place- to let the pros have a look. They've replaced everything but the master cyl and lines, and these are "lifetime brakes". Any ideas on how to get a refund if they can't fix it?

 

[heyhar]

Isn't there anyone in your area that can turn drums? Over the years I've gone through a lot of what you've described, mostly with my '92 XJ, and it always had to do with the rear brakes. But I haven't had one problem since July 4th, 2006. That's the day the hard line to the rear broke. I got the car home, thanks to the dual master cylinder still working the front brakes (ironically I was heading to the junkyard!). Got the car home, got new hard and soft lines, put 'em in, bled 'em, and it's been perfect ever since.

As it turns out, the hard line was full of crud, and the soft line to the axle was just as bad. Step on the brake, and you can force the fluid to the cylinders. Let off the pedal, and what's going to force the fluid back out of the expanded wheel cylinder? Certainly not the brake shoe return springs, especially if they're more than a few years old. I first ran into clogged lines on my daughter's '93 Sable. The rear soft lines were so bad that the pads went right through the discs, as they weren't releasing, and every application of the brakes just shot a little more fluid in, with no chance of escape. The calipers were less than a year old, and they worked fine afterward, and the braking action felt brand new after replacing all the soft lines.

Maybe what I'm trying to say, is look outside the drum, at anything and everything all the way back to the pedal.