brakes sticking and ABS light on?

Okay everyone, in my last post I told everyone that I got my 99 cherokee for 1200 bucks with a blown brake line that had only 89,000 miles on it. I thought that I was getting an awsome deal, now, after replacing the brake line, the ABS light is still on. When I bought it, I thought that if I fixed the line, and maybe cleaned the ABS sensors that everything would be good. Now with that being done, when I drive it, the ABS remanins on, and the front brakes stick. They get very hot, they stick so bad that I need to put it into four-wheel drive to get it to move after a red light or stop sign at the end of an off ramp. I can push the calipers in manually with a screw driver with no problem once it cools off, I have not tried it when it was hot. I don't know if the ABS light is related to my front brakes locking up...? After they cool down, there are no issues, it rolls and drives good until I get about 7 to 10 miles on it and it starts acting up again? Has any one else ever had this problem? I would really love to get this thing back to running operation. Thanks everyone.

Replace the front soft brake lines and the calipers.

Check the ABS fuses and relays. The ABS may need to be put on the diagnostic tool at the dealership.

I have changed the relays on the ABS already with no help to my problem. What would changing the soft lines do for me? I have clean brake fluid in the entire system, when I replaced the brake lines that were broken, I blead clean fluid into all four brake bleader screws.

Soft brake lines deteriorate and can act like a valve, not allowing the brake fluid to release the caliper.

Thanks, I'll give that a try.

Have you put new front brake discs or unit bearings on it? 1999.5 was the split and there is the possibility the wrongs ones could have been put on there, resulting in major front brake alignment issues.

I personally have not changed anything with the front brakes with the exception of the front brake line. My XJ was manufactured in august of 98 according to the door sticker. It seams odd that after the previous owner had it for almost 89 thousand miles that all of the sudden the front end is the wrong one? I thought that the only differance in the 99 split was that it recieved the 0331 head to keep up with the new standard in EPA polution requirements? I'll take a look under there and see what I can find. Thanks for the suggestion.

Tim_MN said:

The ABS may need to be put on the diagnostic tool at the dealership.

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Will cost a few bucks, but best to use your Jeep technology to pinpoint this problem. You could choose to do the repair yourself after the diagnostic is run if you wish.

outracing said:

I personally have not changed anything with the front brakes with the exception of the front brake line. My XJ was manufactured in august of 98 according to the door sticker. It seams odd that after the previous owner had it for almost 89 thousand miles that all of the sudden the front end is the wrong one? I thought that the only differance in the 99 split was that it recieved the 0331 head to keep up with the new standard in EPA polution requirements? I'll take a look under there and see what I can find. Thanks for the suggestion.

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Its not that it could have the wrong front end, its more that if the PO replaced either a brake disc or a unit bearing shortly before selling it to you, he could have put the wrong one on there. You can't really discount the possibility since the brakes were already inoperable when you bought it. The unit bearing and the brake disc need to match:

http://www.naxja.org/forum/showpost.php?p=245269210&postcount=22

Also, I had an ABS light on recently. Turned out to be a loose connector where the rear sensors plug into the module under the rear bench seat. Pushed it back on there and the light went away. Check all your connections twice before paying for a diagnostic check. Also, you can check whether a sensor is shorted out or not by testing the resistance. I don't have the numbers on me at the moment (I'm at work), but I could probably look them up for you tomorrow some time.

Okay, Well here is the update guys. Tried replacing the brake rotors and pads. The calipers feel fine. The piston moves free on both sides. I have fresh brake lines and fluid in the entire system. I drove it today and the brakes still get hot, smoke and lock up. When I pulled it into the driveway I laid down under my XJ and opened the bleeders on both side. The fluid just barly trickled out, so the system to me says that it is working fine. It is not pushing fluid needlessly and causing them to lock up. I guess it could be something with the ABS. Is there any way that some how the ABS is causing the system to apply brake pressure while driving? I guess I could take it to the stealership and see what they have to say about what might be going on. Still, any help over this weekend would be really awsome guys. I'll check the connctions on my abs sensors and report my findings. Thanks for all your help thus far everyone. Keep the suggestions coming.

Hey 1717 Thank you for the link! I took the wheels of my xj, and compared the hubs. I must say, I am a little disappointed in autozone. When I looked, one hub was different from the other. I replaced the brake disks today and when I walked in they said nothing about the different hubs/bearings. I will look in the morning and see what I can do to potentially rectify my problem.

If the ABS is malfunctioning, it simply doesn't engage. The brakes work normally as if the Jeep were non-ABS equipped.

fyrfytr1717 said:

..... if the PO replaced either a brake disc or a unit bearing shortly before selling it to you, he could have put the wrong one on there. ....

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If the rotor and unit hub are mixed across the 1999.5 change over, the rotor physically binds and the Cherokee won't even move out of the garage or driveway.


New brake hoses are less than $10 each, just get some new ones. Myself, I would get some new calipers too.

Just checked my FSM, looks like the resistance of the sensors should be between 900 and 1300 ohms. If I recall (again my notes are at home) I checked four sensors and they were all between 1015 and 1040 ohms. Also, the correct air gap between the sensors and the tone rings should be 0.014-0.059" for the front and 0.036-0.050" for the rear. You can use a feeler gauge to measure this.

outracing said:

Hey 1717 Thank you for the link!

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You can thank Tim_MN ^^^ for the post, I just linked you to it.

Tim_MN said:

If the ABS is malfunctioning, it simply doesn't engage. The brakes work normally as if the Jeep were non-ABS equipped.

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This seems right to me, but I couldn't verify it in the FSM so I didn't want to say for sure. When I pull the fuses/relays in my system it definitely feels like normal brakes. However, when the the fuses/relays are in place but my ABS light is on, the brakes feel kind of crappy. Maybe it's just a mental thing having to stare at that damn ABS light. Regardless, according to the FSM it just sets a code in the memory when the ABS system doesn't pass its self checks.

Tim_MN said:

If the rotor and unit hub are mixed across the 1999.5 change over, the rotor physically binds and the Cherokee won't even move out of the garage or driveway.

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I've never had them mismatched so I wasn't sure just how bad they bind up. I was thinking if it is just a matter of offset (and you could actually get the caliper over the rotor) that just one brake pad would be rubbing continuously on the rotor, possibly causing smoke and eventual lock up like he was describing. Is it actually impossible to get the caliper into position with new pads if you have the wrong unit bearing / rotor combo? Or does it completely lock up once you tighten down the lug nuts on the wheel?

Tim_MN said:

New brake hoses are less than $10 each, just get some new ones. Myself, I would get some new calipers too.

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Think he said he already replaced the fluid and lines throughout the system. Along the lines of replacing the calipers, do you think maybe the caliper guide rails on the knuckles could have that notch worn into them causing them to hang up?

fyrfytr1717 said:

. I was thinking if it is just a matter of offset (and you could actually get the caliper over the rotor) that just one brake pad would be rubbing continuously on the rotor, possibly causing smoke and eventual lock up like he was describing. Is it actually impossible to get the caliper into position with new pads if you have the wrong unit bearing / rotor combo? Or does it completely lock up once you tighten down the lug nuts on the wheel?

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Everything will assemble like normal, but when you torque the lug nuts the mismatched rotors/hubs physically jam up and the Jeep will not move.

The usually cause of disk brakes that get stuck as described by the OP, is failed hoses or failed calipers. Replacing calipers and soft hoses is a normal maintenance item, they wear out with age and use just like tires or u-joints. Failed calipers don't feel any different than good ones, they just get hot as described.

Caliper wear grooves in the knuckle are obvious and easy to repair with a little welding and a grinder.

If the ABS fails, the brakes work like normal, there is no difference in "feel" between ABS/non-functioning ABS/non ABS equipped brakes.

Okay guys, here is the deal, as promised, here was my problem and solution. The previous owner replaced one wheel hub/bearing unit. When she replaced it, the wrong one was installed. The rotors were correct for one side, however, the new hub would cause binding with the rotor that was not designed to work with it. After about 10 miles it would get super heated and cause a lock up forcing me to the side of the road. I went to the salvage yard where they had a grand cherokee with the style hub that I was after. And as a bonus, it had been reciently replaced. For 9 bucks I got a used timken aftermarket hub unit. I bolted everything back into place and drove for almost 30 miles, no smoke, no heat no problems. Now I just have to figure out the ABS light, that is not as important to me, I dislike the light on the dash, but at least my xj is back on the road and trails!

Glad you got it figured out! Kind of had a feeling that was the issue. I guess even with mismatched hubs/rotors you can make the Jeep move if you try hard enough...

As for the sensor resistance values I promised you, I had the range right but was off by 105 ohms. I measured two right rear sensors and two left rear sensors. The right rears were 1110 & 1115. The left rears were 1125 & 1135. I've never measured the fronts, but they should be within the FSM specified 900-1300 ohms as well. Easy to test, just unplug the connectors for the sensors and connect your DMM to the two leads. Take a reading with it set to the 2000 ohms range.

If the ABS light is bugging you and you don't want to deal with it right now, you can pull the relay for it. If you want to disable the whole system, you can also pull the 20A & 40A fuses for the ABS controller. The relay and fuses are all located in the PDC under the hood. You can drive with the system disabled with zero issues.

As I already mentioned though, before giving up on the system check your connections, measure your sensor/tone ring gaps, and test your sensors so that you can rule them out. These are all easy fixes and are relatively cheap (especially at the junkyard). If they all check out OK then you have a bigger (more expensive) issue and you'll have to decide whether its worth fixing or not.

That is the thing, the rotors are only 1/8 inch different. I didn't have to try to make it move, when I put it in gear, it would roll no problem. It was only after that 7 to 10 mile mark. Thanks for all the info on the ABS, I printed it out and will hopefully have some time to look at things not this weekend but the following. I'll post my findings. a special thanks again for all the help to fyrfytr and tim!