arizonajeeper

Hi folks, I've got a 99 XJ that is making something of a vibration/mechanical noise when accelerating at the top ends of second through fourth gears... if I back off and give less gas, the noise goes away. It does not occur in neutral with rev'd engine, only with drive train engaged. Fluids all appear fine... Appears to be getting worse.

Appreciate any diagnostic ideas, as always.

Earl

TRCM

check u-joints on rear driveshaft, and check for shiny spots on the driveshaft that may indicate a weight came off

what kind of noise/sound ?

cyclic humming, rattle, clunk, etc

do you get a vibration at the same time ? if so, where do you feel it ?

rear of vehicle, under seat, steering wheel, etc.

is it worse when turning or not ?

is it worse when in 4wd or not ?

does it do it backing up as well as moving forward ?

do you hear chirping birds if you drive around slowly with the window down ?



.

arizonajeeper

Did a quick inspection of driveshaft, didn't see anything outstanding, but didn't look for shiny spots, will do. Sound suggests vibration, though I don't feel it. Almost a grinding, but not really, kind of a rumbling. Not cyclical - steady. No chirping. Not worse when turning. Mainly been running in 2WD.

Thanks!

Rogue4x4

Crawl under. Grab the driveshaft. Wiggle. Any play?

Any lift? SYE? Anything else we should know? Recent work? Angles ok?

Short of that, remove the rear shaft, drive it around the block in 4wd. Sound gone?

Report back.

arizonajeeper

Will do. I'm actually running a Grand Cherokee driveshaft, been fine for about 5-6 years. Recent work, added a complete exhaust system, banks header, everything early last spring, don't think that's involved, not seeing any smoke from header or exhaust, and runs great when throttling up under the hood, no vibration. All new motor mounts at same time. No vibration from engine.

So yeah, I think rear drive shaft is a good lead, have manual, too. Will check for play.


Thanks.

TRCM

make sure the new exhaust isn't touching the driveshaft anywhere at any time....under load (which is when you hear it) the driveshaft will be in a slightly different place than when you crawl under it and look.

also make sure your e-brake cables aren't rubbing a tire or rim...I've had that be the source of noises like this before from rubbing on a rim

Also, check the rear brakes and make sure you don't have any internal issues like a cracked or broken shoe, and make sure they work....if you snagged an ebrake cable off road, it may have pulled the shoes enough to damage the cable and the internal parts of the brakes, especially if the cable is stuck now and can't release


remember, throttling up under the hood is NOT the same load on the drivetrain as driving.....and you WILL not hear things that way that you will actually going down the road. YOU can approximate some things by power braking the vehicle, but with a manual transmission, that is tricky without causing even more problems


.

arizonajeeper

Awesome, thanks.

cruiser54

Look here:

arizonajeeper

Does appear to be exhaust pipe having settled and started vibrating on the crossmember. Thanks so much, folks.

cruiser54

Check your trans mount.

arizonajeeper

Yeah, suspect I have an issue there.