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clunk sounds on take off.

B

BORA 18T

NAXJA Forum User
Location
Connecticut
I'm a bit new to the jeep world so bear with me. Since I've had the jeep(3 months) on take off there is a clunk sound coming from underneath and it's driving me nuts. Does anyone have any idea what it could be. control arms?, driveshaft? Any ideas?
 
It may help to get a little insite on what were working with here. What year is your Jeep? Any modifications? It could be anything? Can you pin point if its front or rear? Does it do it everytime or just hard accelerations? As much info as possible to help narrow it down. Does it do it when you shift from reverse to drive? If so stand next to the jeep crouched down and listen as a buddy rocks it from Reverse to drive and back to reverse.
 
What year? Some of them have problems with the driveshaft sticking on the slip yoke out the back of the transfer case, and when you leave a stoplight, it will clunk and settle a little bit. If this is you, remove the driveshaft from the slip yoke and rub plenty of high pressure grease on the output shaft of the transfer case.
 
Try to determine just where it is coming from, and whether it is regular, or relatively irregular. Try also to see what conditions might make it vary. Different gear, difference in 4WD vs. 2WD, forward or reverse, turning or not turning, etc. The more info the better. And while you're at it, it sometimes helps to know the year, and whether it's an auto or stick.

One of the more common clunks on an XJ occurs when the engine and transmission mounts get old and sag a little, and the exhaust system hits the frame crossmember. Clearance is small at best there. I suggest as a first step you crawl under there and start yanking and wiggling on things.

If the clunk seems more related to speed, I'd look at the rear driveshaft first, and possibly also the bolts that hold the torque converter to the flex plate if it's an automatic.
 
Ditto on the motor mounts. I had a disturbing clunk for a couple of years whenever wheelin or on hard acceleration. While changing the exhaust manifold I noticed the drivers side motor mount had no rubber! Luckily I had an YJ motor mount in my emergency kit and it fit. No worries.
Also the the tail pipe mounting bracket that is attached to the trans mount makes a racket too when bad.
 
I had a clunking on mine under acceleration. Looked under the hood, there was no motor mount left. The metal was there, but, the bushing was not, so, replaced that, and, no more clunking. Hope this helps.

Tylor
 
Sorry for the lack of info cause I was runnin out the door and typed it up quick. It's a 96 xj, 4.0l, n249 transfer case, 91000 miles, command trac 4 wheel, and a chrysler 8.25 rear end. The sound seems to be coming from the front area. When I put it in drive or reverse and as soon as the jeep jerks when the drive engages theres a clunk and a jerk forward. Same goes when I take off under normal acceleration. I thought about the mounts so I'll check that first as soon as it warms up a tad. Thanks for all the replies.
 
I'd start with Jackhills idea. It's very common and it's very easy to rule it out. Just unscrew the 4 8mm bolts holding the rear driveshaft to the pinion. Pull the driveshaft out of the transfer case. Put a liberal amount of grease down inside the boot of the slip yoke (I used axle grease). Put the shaft back on. Drive it. Worked for me. I had guys telling me it was tranny or t case issues. I checked it on a whim. Good thing too.
 
I've still got a clunk in mine, Engine mounts were busted clean in half on both sides, transmission mount was worn terribly (new one raised the transmission nearly an inch) Replaced my control arms with adjustables. There's still a clunk in my rear end, I'm going to the ds ujoints and the yoke idea next.
 
BORA 18T said:
Sorry for the lack of info cause I was runnin out the door and typed it up quick. It's a 96 xj, 4.0l, n249 transfer case, 91000 miles, command trac 4 wheel, and a chrysler 8.25 rear end. The sound seems to be coming from the front area. When I put it in drive or reverse and as soon as the jeep jerks when the drive engages theres a clunk and a jerk forward. Same goes when I take off under normal acceleration. I thought about the mounts so I'll check that first as soon as it warms up a tad. Thanks for all the replies.
Click to expand...

Sometimes a friend and a critical eye can help a bunch... Either you or they launch & recover o recreate the clunk while the other lays SAFELY alongside and eyeballs different areas that are suspect.

First off, try to isolate the noise

Insure there is NOTHING loose in the inside that is clunking... Chasing ghosts sucks...

Then insure both driveshafts/outputs/pinions are tight at both ends... twist the driveshafts & push each end up & down ... There will be some rotatonal slop (shaft splines) but should be little to none at the UJs or much H&V slop at the TC outputs or pinions.

A 96 that one is unclear if it's ever had motor or trans mounts? I'd look there too! XJ 4.0 motor mounts take a beating & weren't too HI - Q even new. The rear mount is more stocky, but I'd replace all three at the same interval.

Other than that, check the spring U-Bolt torque and/or mark some tell-tale lines to see if the rear axle is shifting around under the springs. Typing correction fluid or paint-pens are great for tell-tales or checking for interference.

FWIW I chased a front end squeak around for a couple months, it was a dry 260 UJ cap that died. The three other caps were healthy & supportive. Only the 'critical eye' seeing red dust and clearance caught it.
 
HossHoffer said:
Check the motor mounts first as they are notorious for clunking.
Click to expand...
x2

replace all the mounts, motor (left and right) and tranny at the same time and be done with it...
 
Ok, well seems like the mounts are first to check then I'll work my way thru the control arms and the driveshaft. Thanks alot for the help everyone.
 
Motor mounts are noisy with throttle. U-joint at rear diff noisy
when initial momentum (foot off brake to gas pedal) changes.
Trac-bar bolts, steering box bolts noisy when wheels are turned
HTH
 
Mine does the same thing and i think i have narrowed it down to the ujoint the right side of my front axle. when you engage the transmition it *clunks* and jerks forward a bit. ive yet to fix it but this is what i believe it to be.
 
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