I installed a 3.5in suspension lift on my 89 Grand Wagoneer recently. The first drive everything was smooth. But after about 100 miles I noticed a small vibration that only occurred during acceleration. As soon as I let off the gas everything was smooth again.
Two weeks later and the vibration is pretty bad. Could it be U joints? Do the U joints go bad after installing a lift? Anything else I can look for while trying to diagnose this problem?
The lift kit you install screwed up the driveling angles carefully engineered to make your GW smooth. Now you have to fix what you screwed up by shimming the pinion angles of the drive axles so they don’t vibrate.
I’d start by replacing every U-joint and have both driveshafts balanced while they are out. Then read upon what the proper driveline angles should be - in most any good 4WD driveline vendor’s website. Then figure out if you can buy, or need to fabricate the proper shims.
Second Mustangman. Keep in mind that U-joints can be bad even while not showing any looseness.
I’ve also run into that driveline angle situation a few times myself.
I ran into that when I lowered my Mustang. It took an adjustable upper rear control arm to dial it back in.
Last one I ran into was an independent rear suspension and it took some shims to tilt the differential a bit. At least that one was comparatively simple.
The OP said it was smooth on the first drive. I wonder if the U-joints were going bad and the new driveshaft angle finished them off? What do you think?
I think that is a very real possibility. Running the joints past the “happy place” they’ve run in for 31 years to a place they’ve never been before probably isn’t doing them any good.
I wonder how old the u joints are on this '89…
With a live axle, is the required alignment where the angle of the driveshaft coming out of the transmission is the same as the angle going into the differential?
That’s the way I’ve always read the recommendations. Equal angles at the trans and rear. But there are limits to how far a U joint can be angled. 3.5 inch lift isn’t so awful large for the rear driveshaft. Might be a bit much for the front, though.
Sometimes with some variation on that rule for axle wind-up on cars with softer springs and powerful engines. Probably not the case here.
From loose wheel weights to incorrect set back on the wheels and everything in between needs checking.
Oversized wheels and tires put a lot of stress on the hub bearings and if the wheel offset is increased outward the added stress is exponentially increased which can cause a wheel to set up a harmonic wobble as the tire turns and the tires set up a cupped pattern as a result. And as the cupping worsens it actually adds to the wobble. On old solid axle Fords I made it a habit to check all the bearings and when correct I increased the caster incrementally with shims and played with the toe until it worked. Re-engineering is again necessary to accomplish such modifications satisfactorilly