Hey guys, I dont post on here very often, but im trying to get this issue figured out because it is driving me crazy. I have searched and researched for weeks and cant come to a definite counclusion what this problem is. So here is all the info about the problem:

1997 Cherokee Sport, 5 speed transmission, 217,000 miles.

When I am driving and apply moderate brake pressure, I get a very loud "bang" from the rear of the jeep. This is usually accompanied by a surge of sudden braking power from the rear, and I can feel it in the brake pedal. This doesnt happen when applying very light brake pressure, but moderate. Also, it usually will only do it one time per each driving cycle. Once it does it, it tends to not do it again until after Ive come to a stop and started moving again. It is not a continuous "bang bang bang..." until the jeep stops, but one single "bang". It WILL NOT do this if the jeep is stationary. It ONLY does it when moving. Also, if I am moving and slowly start pulling up on the e-brake, it seems to have no effect until I get to a certain point, then the "bang" happens and the brakes grab. But the e-brake works normally when the jeep is parked.

Also, I dont know how this could be related, but the other night I was troubleshooting this and took off from a stop relatively quickly, heard the "bang" noise again, and for some reason my back brakes grabbed pretty hard. Like the e-brake was pulled, but it wasnt. I drove it for a few seconds like that and the brakes released somehow. The e-brake handle and cable are new by the way.

The brake fluid reservoir is full and it is definitely not air in the lines. It is a very definite sound, like someone is hitting the underside of the jeep with a sledge hammer when it happens. Hopefully you guys can give me some help figuring this out. I would be glad to upload a video showing what it is doing if there isnt a minimum post count needed to upload vids. Sorry about all the "Bang"s lol.

 

Have you checked the drums? A noise from the back under braking makes sense to check that first

 

Pull the brake shoes clean the rust off the 3 or 4 raised areas on the backing plate the shoes ride on. Apply a very small amount of synthetic wheel bearing grease there and a little on the threaded portion of the self-adjuster, reassemble. While your there check to make sure the drums are in spec. Also make sure the u-bolts and shackles are secure.

 

To 93XJLI, I checked the drums a while back when I disassembled everything trying to find the problem. They seemed fine, still pretty smooth and like they had plenty of life to them.

To Turbo X J, I will try that, I didnt take the shoes off last time. I took the drums off and cleaned everything with brake cleaner. I will try that though. I also thought about checking the u-bolts, because to me it seems like a driveline sound from somewhere, like hitting the brakes is making something move and smack something else.

 

I test drove a Jeep last week that was doing the same thing. I'll be watching this thread for a solution. I too agree that something felt like it was physically moving back there. And the brakes were SUPER sensitive, which is the opposite of what an XJ is supposed to be lol.

 

Don't know if you have a 4x4, but if you do, have you tried greasing the slip yoke? Right where the driveshaft comes out of the back of the transfer case there is a rubber boot covering the splined connection. I had a noise/feeling similar to what you are describing and greasing the fool out of that splined connection fixed my issue.

The trouble was the yoke was sticky so when I braked or started forward from a stop it made the entire Jeep bump or jerk. Lots of fresh grease loosed it up again.

 

My 90 used to do that whole bang but from takeoff after applying moderate brake pressure. I never did figure out what it was as I sold it but I did post on NAXJA about it. Only one person posted back who said it was a sticky wheel cylinder, which now that I think about it, makes sense. My theory is it sticks and pressure builds up and is held down as potential energy by the cylinders. When they finally let go it's instant and causes the drums to expand outward explosively.

Pull your drums off and check them. If the boot is off and/or there's rust on the cylinder, replace them.

 

Yeah the slip yoke was one of the things I was going to try too, mine is a 4x4. It is possible that that is it so I will check it out as soon as possible.

Crimsondragon, now that I think about it the cylinders do seem like they could be the problem also. I'll have to check em out.

By the way thanks for all the quick replies guys, I'm getting an order of things set up so I can tear it apart and check everything at one time.

 

My jeep is doing the same thing. I am probably going to do the Grand Cherokee disc brake swap.