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Old 11-16-2010, 01:22 PM   #1
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Default Help! Violent Shaking / Pedal Pulsating While Braking?

Hey all, just bought an '87 Cherokee Pioneer, 4dr, 4wd, with the 4.0L, AW4 and NP231. Picked it up yesterday and though it has 229k on it and needs some work it seemed to drive okay. Brakes seemed a little weak, and it seems like the pedal is a bit spongy at first, and then gets harder the further it's depressed. But I've never owned a Jeep so I was thinking maybe that's just how the brakes are on these.

Today I was driving pretty slowly through a neighborhood when I went to stop at a stop sign. I applied the brakes with normal force and out of nowhere the truck started to shudder badly and the pedal was pulsating up and down quite a bit at the same time. I was startled and hit the brakes harder and it just shook and pulsated even worse. The shuddering/shaking feeling coming from the suspension isn't the normal vibration of slightly warped rotors, it's much much worse. And the pedal isn't just pulsating rapidly like in an ABS vehicle, it was actually pushing itself back against my foot as I tried to push it down. And any braking ability more or less completely gone now.

I was closed to home so I crawled through the neighborhood at a couple mph in first gear, using the e-brake to gently coast to a stop at each intersection. Using the e-brake, it seemed to work normally (though weak) on the first couple stops, but by the last couple stops nearest to my house, the same shaking & shuddering was happening, although I could feel it was only coming from the rear brakes this time, where as when braking with the pedal I felt it more in the front end.

Do you guys have any idea what could cause this? Though the brakes seemed a bit weak before, I didn't get any vibration from them at all, and the brake pedal pushing back at me is what seems really weird.

I'm about to go pull the wheels off & visually inspect everything, starting with looking for anything obvious, i.e. warped or broken rotors & drums, broken or missing pads & shoes, loose calipers, cylinders and mounting hardware.

I also have a clunk happening when I go over larger bumps that I had assumed is most likely a bad suspension bushing or bushings. I assume any play in the suspension might be amplifying the violent shaking sensation. Anything in particular I should check out?

I have another car, but I bought this Jeep hoping to be ready for the snow that might be coming in as soon as a couple days. I don't need it to run perfect just yet but I definately need the brakes to work!

Last edited by WantACherokee; 11-16-2010 at 01:27 PM.
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Old 11-16-2010, 01:31 PM   #2
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It really does sound like warped rotors, but you've got drums in the rear...
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Old 11-16-2010, 01:34 PM   #3
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^^ That's what it sounds like to me.
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Old 11-16-2010, 01:38 PM   #4
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your drums are fine but new shoes are in your future cuz thats your e-brake
the front rotors are most likely warped or the caliper is shot
also to minimize dw invest in a new steering stabilizer
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Old 11-16-2010, 02:10 PM   #5
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Wow, I'm really impressed by how fast you guys replied. Thanks a bunch for responding to my post.

I just pulled the front wheels & while the pads are new like the seller said, the rotors look pretty old. I can't tell if they're warped with them on the Jeep, but they look pretty worn out. Control arm mounts look really solid as far as I can tell without unbolting stuff. Upper shock mounts seem a little loose. A couple of the tie rods are pretty loose as I knew would be the case based on the loose steering feel. As far as I can tell the calipers are bolted on solidly and no brake hardware looks like it's about to fall off. Can't tell on the condition of the calipers themselves just yet, I'll probably have to pull them and get a better look to make sure I don't have a stuck piston or anything. Any tips on how to determine if that's the case?

I found something really alarming though- the passenger side front brake hose has a big split in the rubber casing and I can see the fiberglass underneath. Aha. Do you guys think this could be the cause of the sudden brake issues? It looks very recent, as the fiberglass inside the split it clean but everything else under the jeep is muddy as it should be.

So without question I'll definately be replacing the front rotors and brake hoses on both sides...

I'm off to go pull the rear tires and check out the back brakes- be right back with an update on those once I take a good look.

Last edited by WantACherokee; 11-16-2010 at 02:17 PM.
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Old 11-16-2010, 03:16 PM   #6
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Checked the rear brakes... I mean, what rear brakes? The friction material on the driver side shoes had separated itself from the metal plate it's bonded to. I found a big time rear wheel seal leak that probably had a lot to do with that. The passenger side brake shoes are still intact, though pretty worn and the friction material is cracked on one of them.

So, I can pretty much assume the back brakes weren't doing much work at all, no wonder they seemed so weak. Maybe the front brakes being overtaxed is what contributed to passenger side brake hose splitting? Does that make sense?

So I'll add rear brakes shoes and hardware and an axle seal to the parts list. I'll think I'll have a shop check the rear drums to make sure they aren't warped. They look okay to the naked eye. The brake fluid is dark brown and nasty so that needs to be flushed out and bled properly.

Am I overlooking anything? How can I tell if I need to replace the self-adjuster screws or wheel cylinders? I don't want to replace anything necessary since I may want to upgrade the brakes anyway if I end up keeping this particular Jeep.
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Old 11-16-2010, 03:31 PM   #7
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When the pedal pushes back can you tell if any wheels are close to locking up? it kinda sounds like a bad caliper but if it's coming from the back, then that's weird. When you said the friction material broke off of the metal shoe was it one shoe or both that it fell off of? Maybe if only one shoe lost it's friction material and the drum is warped a little then as it turns it would push back on the one shoe with friction material still left... with force. But a drum warping that bad would be a feat. idk, just some more suggestions
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Old 11-16-2010, 04:05 PM   #8
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When the pedal pulsates and the truck starts to shake and shudder it actually feels like the brakes are locking up and releasing rapidly.

Both driver's side brake shoes were off their metal backing plates and one of them was split in two pieces. I actually took some pics, hope it's cool if I post these, links are there too if the pics don't load, take a look...

separated brake shoes
Click the image to open in full size.
http://i931.photobucket.com/albums/a..._shoe_fail.jpg

split front brake hose
Click the image to open in full size.
http://i931.photobucket.com/albums/a..._hose_fail.jpg

BTW I also found that this brake hose is also cracking right under the fitting where it bolts to the hard line... definately gonna replace these, might wanna do the rear soft line as well just to be safe, I assume these are 23 year old original parts...

Last edited by WantACherokee; 11-16-2010 at 04:09 PM.
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Old 11-16-2010, 04:16 PM   #9
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If you can compress the brake caliper its usually OK, if not, its seized. Make sure to pull the cap off the brake res, you are pushing fluid back into it.
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Old 11-17-2010, 03:24 PM   #10
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Thanks again for the advice guys. I think I am gonna get stock replacement rotors, front & rear brake hoses, rear shoes and hardware, have the drums checked out & inspect the calipers closely and replace those if they are bad as well.

I'm a big fan of upgrading brakes... I was reading the tech write-ups and see some people put Grand Cherokee rear discs and master cylinders on their XJ's. What about the front brakes? Do people swap GC brakes on the front as well, or do any other inexpensive caliper/rotor upgrades exist that don't require a lot of custom fab or expensive parts? For now I'm just gonna get the stock brakes working properly as time is an issue, but I was just wondering because I was surprised how small the XJ front brakes are for a vehicle this heavy.
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Old 11-17-2010, 04:08 PM   #11
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"rule of thumb" steering wheel shakes rotors warped, brake pedal pulsates rear drums egg shapped.I,if you got the funds new rotors, pads, calipers and lines, drums wheel cyls hardware kits brake shoe rear line your good to go for a long time
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