a different kind of vibration

ok rebelrat dropped of his XJ at my house to work on since he's not that familiar with jeeps yet. he wants to install a 3" lift, but first he wants to work out any bugs that it has in it.

it's a 89 XJ, 4.0L, AW4, 242, D30/D35.

he told me that at 65mph it start vibrating really bad and only gets worse from there. and it won't stop until you get back down below 60mph. so tonight i took it for a drive expecting your typical front end vibration or possibly death wobble, or some driveline vibs. but once i hit 65-70mph, i was just plain baffled.

the "vibration" is in the entire vehicle. it's not in the front end. it's not uncontrollable or "scary". you CAN NOT feel it in the steering wheel, and you CAN NOT feel it in the seat (not like rear driveline vib). the only way that i can describe it is as if i was driving over those ribbed caution/wake up strips on the side of the highway, or as if i was driving a track vehicle.

it absolutely doesn't interfere with the driving. the vehicle tracks nicely with great alignment, and otherwise feels great. it does feel like it needs to shocks. but this vibration has got me stumped. i've never seen/felt anything like this. any clues???

It sounds exactly like the vibration mine has. My vibes start at 55mph though.

My vibes only showed up after I had the front spiders welded (lincoln locked). This caused my front drive shaft to spin at all times unlike before.

I'd suggest taking the front shaft out and take another test drive.

Tally_XJ said:

I'd suggest taking the front shaft out and take another test drive.

Click to expand...

What he said.

Also check the rear shaft for worn parts.

i have had 2 rear shafts in it. one known good. no change

i was going to start this weekend by replacing the shocks, just to clean up that part of the ride a bit. then i was planning on pulling the front driveshaft, greasing everything, checking the motor/tranny mounts, and look inside the diffs to make sure there is nothing out of place there.

Tally_XJ said:

It sounds exactly like the vibration mine has. My vibes start at 55mph though.

My vibes only showed up after I had the front spiders welded (lincoln locked). This caused my front drive shaft to spin at all times unlike before.

I'd suggest taking the front shaft out and take another test drive.

Click to expand...

unless i'm way off on this, doesn't the front driveshaft spin all the time anyways with the non-vac D30's??? so why would your welded spiders affect your straight road driving??? just curious.

On the 1989 XJ the D30 axle WAS a vacuum disconnect axle. . . . at least mine is. Without the spiders locked, my front drive shaft did not spin at road speed while in 2WD high.

On a non-disco axle, it does spin all the time regardless. So if his XJ has a non-disco axle, this would be my suggestion that he might have a bad u-joint or worn out double cardan joint in the front shaft or its terribly out of balance or both.

However, I was unaware that any 1989 XJ automatic came with a non-disco axle. Was it replaced? I also didnt know they came with an NP242 transfer case?

they came with both, disco and non-disco axles. his is non-disco

NP242 - "Selec-Trac" part-time OR full-time - 2.72:1 ratio low range - shift pattern 2wd - 4part-time - 4full-time - N - 4LO - used 87-01

242 is what makes a Jeep of that vintage non-disco.

figured i'd throw an update in here.

i pulled the front driveshaft, and went to go on a test drive. about 1mile from the house, there was a loud bang/clank/grind, and the cherokee stoped dead in it's track like i just hit a wall. then at that same time it let loose and rolled again, but it sounded like the drivetrain was about to disintegrate. so i limped it back home. back at the house i put the whole thing on jackstands and drove it in the air and it sounded horrible. so i pulled the rear driveshaft and started spinning the rear axle...that wasn't it.

so i tried turning the output shaft of the t-case, and it would turn/bind/turn/bin/turn/bind.

so i swapped in a 231 i picked up from a wrangler, and went on another test drive.......had it up to 75 with no vibes.

so it was either the front driveshaft or the t-case or both. but the front driveshaft also got replaced, because the double cardan was completely seized up and couldn't even be moved.

not it rides nice and clean, and it just recently got a new exhaust, trackbar mount, shocks, and will be getting a rear axle swap soon, and upgrade the cooling system to open style.