A clunking sound when I brake?

Alright first of I have a 1990 xj with the 4.0 aw4 231 dana 30 and 35 setup. This is whats happening, just tonight I noticed when I come to a stop i feel this thud and hear this clunk thats seems to coming from the middle of the jeep and maybe front end and its only when i come to a stop. I just replaced rotors and pads soo i know my front brakes are good and i have no trouble stopping and I've just had to replace a transfercase and the the transmission is good. I do know my motor mounts are bad and my transmission mount has seen better days, can this be the source to my problem? Or do you think u joints? My right hand side u joint is a little lose same with the one on my rear drive shaft to the diff. Or could it be my slip yoke? I do have a small lift on it with some crappy blocks on the back. So any advice would be much appreciated. Thank you.

groovyjeepster said:

Alright first of I have a 1990 xj with the 4.0 aw4 231 dana 30 and 35 setup. This is whats happening, just tonight I noticed when I come to a stop i feel this thud and hear this clunk thats seems to coming from the middle of the jeep and maybe front end and its only when i come to a stop. I just replaced rotors and pads soo i know my front brakes are good and i have no trouble stopping and I've just had to replace a transfercase and the the transmission is good. I do know my motor mounts are bad and my transmission mount has seen better days, can this be the source to my problem? Or do you think u joints? My right hand side u joint is a little lose same with the one on my rear drive shaft to the diff. Or could it be my slip yoke? I do have a small lift on it with some crappy blocks on the back. So any advice would be much appreciated. Thank you.

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Well, I would start with those.

I got the same noise on my 99 sport. its not my u joints. you ever figure it out?? I could sure use the help.

Make sure your caliper bolts and lug nuts are tight and at least throw a cheap set of motor mounts in it. Check your control arm bushings and make sure the bolts are super tight.

Those are the most common things. Don't rule out ball joints but don't just go throwing money at it.

Don't run it with shot motor mounts or you could end up shearing off the bolts into the block and even ruining the block.

mfarrer said:

I got the same noise on my 99 sport. its not my u joints. you ever figure it out?? I could sure use the help.

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I wouldn't rule out the u-joints unless they're new. When I found my u-joint at fault for the very same "clunk". I also read that I should apply a generous slathering of grease on the slip joint shaft and spline/gear.

Since I did that, no more clunk. I admittedly didn't do a very good job on the u-joint install, I was in a hurry, but thinking back, I didn't clean out the yoke as well as I had wanted. ::note to self:: Re-do u-joint on XJ. It's been bugging me.

Motor mounts can take out a flex plate also. I'd start with them since you know they are bad.

I was having a similar issue, except it was doing this when turning. Turns out all my leaf bushings are shot

My 01 xj did the same thing. The control arm bushings were shot, I replaced them and the problem was fixed.

Locked98GC said:

Motor mounts can take out a flex plate also. I'd start with them since you know they are bad.

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I don't see how this could happen, as the motor and trans are solidly bolted together.
To be sure, bad motor mounts can cause quit a bit of difficult/expensive damage, including leaving you stranded on the trail.

OP: if you have never done your motor mounts, they are likely bad, don't worry though, they can be changed with one guy and a prybar faily easily.

souske said:

I don't see how this could happen, as the motor and trans are solidly bolted together.

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x2

Also, on the clunking sound. It it is the last few feet of the stop and maybe another clunk when you go to accelerate from the stop I would lube the slip yoke at the transfer case or if you have a SYE the slip joint in the driveshaft