Vibrations under acceleration

Ok so lately Ive been having a vibration in the rear of my jeep. Its gotten a lot worse and I want to figure out exactly what it is so I can fix it.

Details:
1990 Cherokee
2inch budget lift
AW4 auto trans
231 transfer case
NEW rear driveshaft and u-joints. (I checked those already)
Tires are properly balanced

The vibration is only under acceleration from a dead stop. It also feels like its grinding a little bit. The rear axle feels like its hopping or atleast the whole jeep feels like it. I know its not the front axle. I have it unlocked and theres no driveshaft going to it. Also the front has new hubs and u-joints. Any ideas? Im starting to think my gears are going bad. or my Tcase is the issue. But the odd thing is it only happens under acceleration and I can feel the whole frikken floor shaking.

I will be pulling the rear axle cover tomorrow and inspecting the gears as I suspect my gears are really worn causing the vibe.

Are you using shackles in the back? Its a stretch but the change in pinion angle could be causing your driveshaft to vibrate:dunno:

If that is the prob, you can get shims to correct.

The shackles are factory. The driveshaft angle doesnt seem to be a problem and the driveshaft itself isnt the problem. Im thinking its either the flexplate or the diff itself at this point as I ruled just about everything out.

do a burnout in loose dirt, does it feel like the rear wheels playing the bongo's? thats axle wrap from burnt out rear leaf springs. this can lead to worn out driveshaft ujoints, which you say you just replaced? what was wrong with them? worn out?

you say budget lift.... what'd you do? add a leafs? have they sagged semi recently?

Check your transmission mount.

xcm said:

do a burnout in loose dirt, does it feel like the rear wheels playing the bongo's? thats axle wrap from burnt out rear leaf springs. this can lead to worn out driveshaft ujoints, which you say you just replaced? what was wrong with them? worn out?

you say budget lift.... what'd you do? add a leafs? have they sagged semi recently?

Click to expand...

The budget lift involved an addaleaf and 1inch blocks. I did the burnout test you mentioned and it seems to be jumping in the dirt quite a bit for the first few seconds then evens out as I give it a bit more gas.

Im thinking its axle wrap now. I took the covers off my diffs yesterday and inspected everything, seems to be perfectly fine. I also took the cover off the trans and looked at the flexplate and looks fine. I even greased all of the greasable joints and whatnot. Engine and trans mounts are fine aswell. I guess its a good excuse to get a real lift now and get full packs.

If budgets a problem, you could allways do a bastard pack with a NEW base-pack.... ie, one that not allready pre worn... the problem is when you add stuff to a 1990 leaf pack.... its tired before you even start... then adding an AAL, and a block just kick it while its down...

my 3" lift started as an AAL, and it eventually started to wrap so badly, i had exactly what you describe... it also took out my driveshaft ujoints, and put a slight tweak in my driveshaft yoke ears.... i had to throw in a slip yoke eliminator, new cv driveshaft, and a set of full leaf packs. but afterwards, it completly went away. this is kinda why people say not to run cheap lift parts... you and i can both vouch that they work... but they can ruin other parts if allowed to.

You shouldnt need a sye at your height though, unless you go 3"+. goodluck.