Exhaust rattle/bang

Posted bout this a long time ago, got some answers and used them. Worked for a long time but...

Basically when I start the XJ I can hear the pipes smack up against the undercarriage somewhere. So far here is what was done and results if any:

A. Bent exhaust tip more to the right as it was close to the tow hitch.
R. Reduced somewhat. Closer examination showed the pipe had been smacking the hitch.

A. Replaced motor mounts (pass side was broken).
R. Discovered while doing this the tranny mounts were toast. Did make it quieter.

A. Replaced tranny mounts. Soft as butter were the old ones.
R. Was quiet for about 1 year which works out to maybe 10K miles, if that. Two wheels are better than 4 personally.

The sound started back up about two months ago. My daughter drives it the most now. She drives like a little blue hair thanks to an accident last year. I've checked the motor/tranny mounts...all good. Exhaust tip is still away from the hitch. What am I missing? All hangers "appear" to be fine. How many are normal? Might I possibly be missing one somewhere?

Sarge

Hey Sarge you could check where the exhaust goes thru the body and trans crossmember. Mine is banging on there now.

Are you sure a pipe is hitting? A rattle at start up could be the Cat conv has come apart inside.When the system is cold, bang it with your fist, if the conv rattles its time for a new one.
Wayne

digger4u said:

Hey Sarge you could check where the exhaust goes thru the body and trans crossmember. Mine is banging on there now.

Click to expand...

Forgot in my post BTW, it's a 2wd. Does that make a diff there? I'll crawl under and check it out.

Sarge

Wayne Sihler said:

Are you sure a pipe is hitting? A rattle at start up could be the Cat conv has come apart inside.When the system is cold, bang it with your fist, if the conv rattles its time for a new one.
Wayne

Click to expand...

I "think" it is. It's a fairly stout sound, actually more of a bang than a rattle, I suppose. It wouldn't surprise me to find out the cat is gone tho...about 130K miles on here now. She's a 2wd the previous owner "thought" was a 4wd. For 3-4 months after I bought it I was pulling river weeds out of wierd and high spots.

Sarge

Mine was making the odd bang sound on dips in the road, finally crawled under there and found the rear U bolt on the tailpipe hanger was gone so I stuck a new one on, bang got worse, the clamp bracket was hitting the side of the skid plate. Loosened it backup and pushed the pipe as far outboard as I could then retightned it, been quiet ever since. My tailpipe was/is also tweaked from a rock getting between it and the side of the skid plate.
Have someone start it up cold and have you or a couple of other people down under there to try to localize the sound. It's hard trying to figure out where it's coming from from the inside, sound could be transmitted thru the metal in the frame/body and leading you in a false direction...

I'm actually at the exact same spot you are... front motor mounts were shot, so I replaced those thinking it would get rid of the loud clunk when I take off in 4lo... it sure did, but then more clunks cropped up (multiple clunking/banging noises) when I take off in 2wd. So, I think after that that the tranny mount is bad, so I pulled the crossmember off and replaced that yesterday, and things got even worse.

After some closer inspection last night, I found that the exhaust itself was hitting the crossmember. Look real close in there where it goes through... what I did was hold a flashlight up there and have someone (make sure you trust them not to run you over!) start the jeep while I watched, and sure enough as soon as the jeep started turning over, the exhaust started banging on the crossmember and making all kinds of racket.

I'm not sure yet what I'm going to do about it... maybe try and bang the exhaust over so it doesn't rattle, heat the mounts up a little and tweak it out of the way, I'm not sure. Kinda silly that after replacing the motor and tranny mounts with fresh ones that this problem crops up... makes me wonder if the exhaust on mine isn't tweaked... either that or it was replaced when bad motor/tranny mounts were in, and the exhaust shop routed it where it would fit, then once I replaced all that stuff, it no longers fits right.