Hey guys, quick question for ya. 1 week ago I had brand new tires mounted and balanced on my 98 cherokee. It drove smooth as butter and all was well. I went ahead and replaced the leafs springs since the stock ones sagged. I replaced the leafs packs with heavy duty crown ones, new rugged ridge leaf shackles, and new u-bolts. Since Iv replaced those things I get a nasty vibration between 37-40mph. Once I accelerate to around 37mph it starts vibrating real bad, you can see the rear view mirror shaking but it goes away right after 40mph and its smooth again. Decelerating it does the same thing once I hit 40mph but its smooth again from 37mph (apx.) until Im stopped. I took it back to costco and had the tires re balanced, this made no difference with the vibration. Can it be the pinion angle even though the leafs arent lifted leafs? I took it to class and stuck it on the alignment rack. Everything was perfect however the rear axle thrust angle is slightly off. I jacked it up, loosened the u-bolt nuts and try to re-position the axle. This didnt change anything. So im thinking its either the thrust angle or a pinion angle issue. Any ideas? I want to fix this before the vibes take out the new u-joints I just put in. Thank you

 

must have lifted it a bit and brought to light some tired out u joints...although i see you put new ones in

torqued your u bolts properly? drive around for a bit and re-torque maybe?

 

Hank, Although I replaced both u-joints in the rear driveshaft, could it be caused from a bad u-joints in the fronit driveshaft or the front axle even though im in 2wd? At first when I installed the new u-bolts I torqued the nuts to 55ft lbs, bumped it up to 60-65ft lbs when I tightened everything back up last night after attempting to reposition the axle.

 

It won't have anything to do with the front...

If it started immediately after the new springs then I'd say it was the pinion angle.

What IS the pinion angle?

 

I have no idea I have yet to check it and I also dont have a pinion angle gauge. I guess this is my next step. Do I check the angle on the rear diff yoke, the driveshaft, and where the ds slides over the tc shaft?

 

^^^^i would find those angles and report back...

 

Will do thank you guys

 

I do not have pinion angles yet however I have the toe and thrust angle specs from the alignment a few days ago. Total toe for the rear is .40*, the rear thrust angle is -.24*. The right rear toe is .44* and the left rear toe is -.04 degrees ??