XwalkerX

so just bought our first XJ like a month ago and every since we got it there has been a weird vibration around 50mph but only at very light throttle and usually its going up a slight incline
to describe the vibration its almost like the tires are rubbing in the rear. it only happens randomly and usually its very quick and doesnt last long

XJ is 2WD and has a 3" coil spacer up front and lift shackle in the rear with JK rubicon shocks
also running ar23 wheels with 31x10.5-15 all terrain tires
most of what i read described vibrations in the driveline as a 4WD issue and needing a crossmember drop but most 2WD XJ owners seem to be unaffected by a 3" lift

it threw a p0740 code once but it was a bit low on trans fluid so we added some and cleared the code
the code hasnt returned but the vibration is still there
i adjusted the TV cable and it got slightly better but i was wondering if it was the synthetic max life dex/merc ATF the previous owner used after a recent fluid change

yesterday did a transmission service and dropped the pan, changed the filter and put all new shift solenoids in.
i was really hoping it would solve the issue as i thought based on the code it was related to converter lock up but again the vibration is still there

i should also add that i did a basic check of the u-joints and they are still very tight with no play in them

im wondering if i should look into a shim for the rear axle to help the driveshaft angle? or perhaps a crossmember spacer? maybe a transmission treatment like lucas?
my rear leaf springs are sagging so i also wonder if its axle wrap?
but again it only does it in 4th gear with the converter locked up and not if i hammer it from a stop light so i dont think its axle wrap...but i could certainly be wrong?
im really at a loss here


here is a pic of the XJ in question

EZEARL

No problems before you lifted it?

"wondering if it was the synthetic max life dex/merc ATF the previous owner used after a recent fluid change" That's the correct fluid. What are you using since changing it?

XwalkerX

I bought it already lifted

I'm running the non synthetic Valvoline Dex/Merc now

Bugout4x4

The first place to always start is the tires and wheels... Seriously, I have seen folks dump tons of bucks into something like this only to find out it was just a tire or bent wheel.

EZEARL

Good point.

If not it may be a driveshaft angle issue. Wonder if your rear springs being weak plus the lift shackles are causing the angle to change under certain conditions thus making the vibration a random issue? I know most here don't recommend lifting the rear if the leaf springs are weak. Also check that the axle is seated proper and not shifting on the spring pads.

XwalkerX

I should also mention that I had stock wheels with 32x11.5-15 mud terrain tires on before I put those all terrain 31" tires on.

Vibration with both sets

SexyDexy

Even though your driveline unjoints seem tight, they can still be dry and have gone bad. If you don't know if they have ever been replaced, it's probably time to replace them (use Spicers).

EZEARL

+1
Could be a number of things though. Hopefully a slightly bent driveshaft isn't one.

Bugout4x4

Same wheels? same rear axles? I would swap stuff around and see if it moves, If not then move on to the more expensive things.

XwalkerX

No I had 32" tires on stock wheels before I put the 31" tires with American racing wheels on

Larry's XJ

I would so the joints first. Cheap and easy.
The theroy being they wear in at one angle then not happy when angle is changed.

I would say no to trans crap, JMHO.

XwalkerX

wel wel did 2 new Spicer U-Joints today and...


nothing has changed.

Larry's XJ

Well cheap peace of mind.
Check trans and motor mounts. make sure exhaust isn't rubbing cross member.

XwalkerX

yeah at least i can rule them out now.

i originally thought it was the exhaust and paid to have it rehung so i know for sure its not hitting anything

i would think if its mounts then it would happen more often than only when the converter locks up

this week im going to check to make sure the TPS tests well. ive been reading that could adversely affect the transmission

ill also be doing the rear wheel bearings and a lunchbox locker this week so ill be able to check the rear end to be 100% certain its not coming from there

Larry's XJ

Though I don't care for the shot gun approach it might get to the point of just speeding up or slowing down.