heyhar
NAXJA Forum User
- Location
- PA (near Poconos)
You wouldn't happen to have a D35 rear, or a limited slip, would ya?
Mystery of the irrepairable drum brake pulsing
- Thread starter @dam
- Start date
You wouldn't happen to have a D35 rear, or a limited slip, would ya?
heyhar
NAXJA Forum User
- Location
- PA (near Poconos)
You don't list where you live, but up here in the Great Northeast, metal parts just LOVE salt. Given the age of your vehicle, I'd be inclined to replace all the lines, just because. I'll bet the brake fluid was not purged every three years/36,000 miles like it should be. Diagnosing the problem the way you've described is tough, as you cannot recreate all of the conditions, heat, load, etc. on a jackstand. You've mentioned that it's a spare car, so now is the perfect opportunity to do some research on the insides of your brake lines. Sixteen years, it's time for new rubber lines anyway.
I've bled the brakes every 3 years since I've had it (2000). Or, rather, had them bled.
Not much in the way of rust on this car. It's lived 5 years in Portland, 3 in Dayton (always had the salt washed off ASAP), 3 years on the CA coast (got a little rust on the windshield header there, due to sea air dripping off my roof box), and 5 years in Albuquerque.
Not much in the way of rust on this car. It's lived 5 years in Portland, 3 in Dayton (always had the salt washed off ASAP), 3 years on the CA coast (got a little rust on the windshield header there, due to sea air dripping off my roof box), and 5 years in Albuquerque.
Update: I may've FINALLY figured it out.
I pulled the wheels off and noticed that I could shake the brake drums around ever so slightly. That means the hole in the drum must be slightly bigger around than the axle flange. Of course, this is necessary to get the thing on, but since the pulsing is always worse when the drum is warm, I thought maybe there was TOO MUCH play- too loose of tolerences. My hypothesis is that when I apply the brakes, the first pad to contact immediately pushes the drum off to one side, and the the wheel and the binding of the lugnuts keeps it there for the rest of the stop. Being slightly off-center, once per revolution braking force spikes. As it gets warmer, it gets pushed further off-center, and then contracts to nearly-centered again when it cools.
I just happened to have some .002" stainless steel shim-sheeting. I cut off a long strip and shook the drum up and down, then left and right, as I'd insert the shim between the drum and axle. I got it most of the way in- just a tiny bit of overhang. Took a while to work in, and there's still a very tiny amount of play, but a small fractionof what was there before. This means I took up about .004" in diameter off of the hole in the drum, and there's a bit more where that came from.
On the drive in this morning, the brakes felt better than in a VERY long time...and these drums are already slightly warped. I could barely detect the pulsation. Of course, this usually happens for a while after a brake job anyway...but I didn't do a brake job.
If this is it, I may take it back to the shop and ask for some drums that fit properly without being shimmed.
I'll update again if this gets worse, but I think I might have it figured out.
This means I took up about .004" in diameter off of the hole in the drum, and there's a bit more where that came from. Do you think that's enough to make a dramatic pulsation? How far out of round does a drum have to be before it's considered warped?
So, how much play do you generally feel between a drum and an axle?
I pulled the wheels off and noticed that I could shake the brake drums around ever so slightly. That means the hole in the drum must be slightly bigger around than the axle flange. Of course, this is necessary to get the thing on, but since the pulsing is always worse when the drum is warm, I thought maybe there was TOO MUCH play- too loose of tolerences. My hypothesis is that when I apply the brakes, the first pad to contact immediately pushes the drum off to one side, and the the wheel and the binding of the lugnuts keeps it there for the rest of the stop. Being slightly off-center, once per revolution braking force spikes. As it gets warmer, it gets pushed further off-center, and then contracts to nearly-centered again when it cools.
I just happened to have some .002" stainless steel shim-sheeting. I cut off a long strip and shook the drum up and down, then left and right, as I'd insert the shim between the drum and axle. I got it most of the way in- just a tiny bit of overhang. Took a while to work in, and there's still a very tiny amount of play, but a small fractionof what was there before. This means I took up about .004" in diameter off of the hole in the drum, and there's a bit more where that came from.
On the drive in this morning, the brakes felt better than in a VERY long time...and these drums are already slightly warped. I could barely detect the pulsation. Of course, this usually happens for a while after a brake job anyway...but I didn't do a brake job.
If this is it, I may take it back to the shop and ask for some drums that fit properly without being shimmed.
I'll update again if this gets worse, but I think I might have it figured out.
This means I took up about .004" in diameter off of the hole in the drum, and there's a bit more where that came from. Do you think that's enough to make a dramatic pulsation? How far out of round does a drum have to be before it's considered warped?
So, how much play do you generally feel between a drum and an axle?
Last edited:
- Location
- MilkyWay Galaxy
Could the metal they are using for the drums be inferior?
I am not a metallurgist and I do not know the specs on the metal for brake drums, but this is starting to sound like cheap, under spec metal used for the drums? Or maybe the equalizer valve (or something else in the brake hardware) is not letting the brake pads release, and so they drag and over heat, thus over heating the drum to where it can warp when it cools while the pads under pressure (like from an over tight parking brake)?
I am not a metallurgist and I do not know the specs on the metal for brake drums, but this is starting to sound like cheap, under spec metal used for the drums? Or maybe the equalizer valve (or something else in the brake hardware) is not letting the brake pads release, and so they drag and over heat, thus over heating the drum to where it can warp when it cools while the pads under pressure (like from an over tight parking brake)?
I'm sure the metal isn't as good as OEM. However, this problem originaly started on the OEM drums. Why they took 175k to start to show problems I have no idea.
I've never paid attention to what 'normal' play between a drum and an axle should be. This hole is at least .005" too big in diameter. Could that be significant? I think it could- imagine what it would take to squeeze the braking material down another .005". It also, however, might explain why I don't really feel any pulsing in the pedal- .005" of pedal travel is nothing (and much of that would be absorbed via line balooning)
I've never paid attention to what 'normal' play between a drum and an axle should be. This hole is at least .005" too big in diameter. Could that be significant? I think it could- imagine what it would take to squeeze the braking material down another .005". It also, however, might explain why I don't really feel any pulsing in the pedal- .005" of pedal travel is nothing (and much of that would be absorbed via line balooning)
- Location
- MilkyWay Galaxy
They would have been much thinner, possibly worn out of spec at 175,000 miles, thin enough to warp even with good metal.
The axle to drum slop is not a problem.
- Location
- Castro Valley,CA
Could of you have bent an axle or may be the bearing has failed. If you have a dial indicator (you can get a cheap one at HF). Attach the base to the housing and check the run out of the axle flange. Check the OD and the face.
I do not think 0.005 is too much clearance; you need at least 0.002 for a slip fit.
I do not think 0.005 is too much clearance; you need at least 0.002 for a slip fit.
anthrax323
NAXJA Forum User
- Location
- San Antonio, TX
A couple tips:
1. Drum shoes are not identical pairs - there is a front shoe and a rear shoe, with the thicker shoe of the two being toward the front of the vehicle IIRC (Joe, I'm sure you know the right answer on this one... Been a while for me).
2. Upon installing the drum, do a basic manual adjustment. The shoes should lightly touch the drum surface, with moderate rotational resistance (free hand, wheel off). Basically, a little on the shy side of "snug".
Just thoughts - you may already be aware of this.
1. Drum shoes are not identical pairs - there is a front shoe and a rear shoe, with the thicker shoe of the two being toward the front of the vehicle IIRC (Joe, I'm sure you know the right answer on this one... Been a while for me).
2. Upon installing the drum, do a basic manual adjustment. The shoes should lightly touch the drum surface, with moderate rotational resistance (free hand, wheel off). Basically, a little on the shy side of "snug".
Just thoughts - you may already be aware of this.
- Location
- In the islands
Not for the life of me do I understand why a warped or out of round break drum would wobble or pulse when hot and not when cold. The Chevy Chevell from the 1970's were notorous for having warped drums. You know it every time you hit the brakes. The same could be said for the Chevy Cavalier I had when I first came to the US.
Do you think there may be something else wrong that is amplified when youhit the breaks,....some on the differential that also get warm over time?
Someone suggested checking the axle flange for runout That may be something to look at. I doubt that would only show up when it is hot, but then again it might. I would put my money on poor quality break parts and or sticking break shoes maybe caused by sticking wheel cylinders, bad return springs on the shoes or just improper installation.
How often do you drive with the parking break applied. Do you drive with one foot or two feet? I am grasping at straws here.
What will be good is to do a check for run-out when the wheel/drum is hot.
Do you think there may be something else wrong that is amplified when youhit the breaks,....some on the differential that also get warm over time?
Someone suggested checking the axle flange for runout That may be something to look at. I doubt that would only show up when it is hot, but then again it might. I would put my money on poor quality break parts and or sticking break shoes maybe caused by sticking wheel cylinders, bad return springs on the shoes or just improper installation.
How often do you drive with the parking break applied. Do you drive with one foot or two feet? I am grasping at straws here.
What will be good is to do a check for run-out when the wheel/drum is hot.
Runnin'OnEmpty
NAXJA Forum User
- Location
- Southeast USA
Anthrax brought up a good point; that the shoes have
different friction lining areas for the forward and rear shoes.
The longer lining with more friction area goes to the rear,
and the shoe with the shorter lining is the front one.
Might be worthwhile to double-check this....
different friction lining areas for the forward and rear shoes.
The longer lining with more friction area goes to the rear,
and the shoe with the shorter lining is the front one.
Might be worthwhile to double-check this....
- Location
- East of Cincinnati
I thought this sounded plausible...
Maybe not even the M/C, but if the proportioning valve was screwed up, it could be putting more load on th rears than they really want to handle.
Can you smell or feel if the rear brakes are getting hot?
Like was said, grasping at straws...
Robert
- Location
- MilkyWay Galaxy
When my daughters jeep was hit on the beach, the drive shaft and tire on the rear took the hit, it bent the last 3-4" of the shaft, outboard side of the bearing, and bent the rear backing plate, Had to replace both the backing plate, and drive shaft and bearings. A real nasty, hard bump, impact with a curb might do the same thing.
Have you tried another brake service shop, or some local jeep guys that know what they are doing yet?
- Location
- MilkyWay Galaxy
X2 on that!!!! I was thinking the same thing.
I've never noticed a smell, but I'll feel for heat next time I drive.
When I run it on jackstands, nothing appears to be bent, but it shakes like crazy when I apply the brakes.
It's had no real impacts that I can recall. It's just my back-and-forth to the ski area or mtb trailhead car...mostly freeway miles (it has 198k and still on the original clutch). Oh yeah- being a stick, that means I'm effectively a one-foot driver as far as brake and gas go. I'm REALLY easy on my brakes, doing a lot of coasting and engine braking. My last shoes were on for 100k. I have another car with a computer that estimates brake life. It says I'll go 90k of MOSTLY CITY DRIVING.
I'll double check the shoes are on correct when I get it later today, but I doubt that is it since the pulsing was there before I brought it in (it's just been a lot worse sense).
I did have one other shop look at it. I asked them to see what might cause the drums to warp so easily. After leaving it all day, they did their standard brake inspection and said "...uhhhh....your drums are warped". Thank you professor obvious.
Wheel cylinders are rebuilt, and all hardware is new. How can I tell if anything is sticking? I still get great mpg, so things can't be sticking too bad.
Any suggestions on how to find a decent mechanic...preferably a Jeep guy? I'm in Albuquerque. I've never really had to use one, and only took it to this brake shop because I couldn't figure out the problem (and because I hate working on drums)
When I run it on jackstands, nothing appears to be bent, but it shakes like crazy when I apply the brakes.
It's had no real impacts that I can recall. It's just my back-and-forth to the ski area or mtb trailhead car...mostly freeway miles (it has 198k and still on the original clutch). Oh yeah- being a stick, that means I'm effectively a one-foot driver as far as brake and gas go. I'm REALLY easy on my brakes, doing a lot of coasting and engine braking. My last shoes were on for 100k. I have another car with a computer that estimates brake life. It says I'll go 90k of MOSTLY CITY DRIVING.
I'll double check the shoes are on correct when I get it later today, but I doubt that is it since the pulsing was there before I brought it in (it's just been a lot worse sense).
I did have one other shop look at it. I asked them to see what might cause the drums to warp so easily. After leaving it all day, they did their standard brake inspection and said "...uhhhh....your drums are warped". Thank you professor obvious.
Wheel cylinders are rebuilt, and all hardware is new. How can I tell if anything is sticking? I still get great mpg, so things can't be sticking too bad.
Any suggestions on how to find a decent mechanic...preferably a Jeep guy? I'm in Albuquerque. I've never really had to use one, and only took it to this brake shop because I couldn't figure out the problem (and because I hate working on drums)
- Location
- Up s*&^ creek with a paddle!
If you are certain that it's inferior drum parts my suggestion is go to a junk yard and buy rear disc brakes off a Liberty and convert yours. Then you have disc brakes. Personally if I had that much trouble I would have grabbed a whole rear end for cheap just to make sure nothing else was wrong. The rear axle is very easy to swap out.
- Location
- MilkyWay Galaxy
I would try a different brand of shoes, and brake drum. Like I said 3 months ago, I got a drum off the shelf from Autozone last year that was at .25" off center, meaning the distance from the center of the drum (based on the center hole) to the inside drum wall varied by at least .25", the drum wall thickness varied by .25" as well. It was total junk!!!! It had been machined off center. It was also made in CHINA!!! You might check a junk yard for old drums that still have life in them?
I would also replace the equalizer valve between the MC and SCs.
Then if that failed, I like the idea just suggested below of swapping out the entire rear axle, but make sure you get one that is not damaged!!!!
I would also replace the equalizer valve between the MC and SCs.
Then if that failed, I like the idea just suggested below of swapping out the entire rear axle, but make sure you get one that is not damaged!!!!
heyhar
NAXJA Forum User
- Location
- PA (near Poconos)
X2 on Mike's idea of faulty drums. Search around, and you'll find threads on 'clunking rear brakes' through the years. I dealt with this on my '92 for a while. If I recall, finally swapping the drums did the trick. Brake parts can deform when hot, as anyone with throbbing, pulsing, chattering discs can attest to. They're OK when cold, but a mess when they're hot. Drums can react the same. With your rig pushing 200K, how old, or how many miles on the drums? Maybe getting too thin? Try new ones, hopefully of higher quality. I think the Far East has a way to go in the field of metallurgy.
