wildbill1

I recently bought a '99 XJ with sacked out springs. I replaced the rears with complete new heavy duty springs and the fronts with coils from a '96 GC. The net lift is 1.25" in front and 2.25" in the rear.

While accelerating, I'm noticing a slight vibration. I plan to replace the u-joints anyway due to age and plan to measure pinion and TC shaft angles while I'm doing the u-joints.

If I understand right, the pinion should be approx. 2-4 degrees "flatter" than the TC output angle, correct? I understand that when power is applied, the torque will raise the pinion and should make the 2 parellel.

My question, after reading about lots of XJ owners doing a transfer case drop is, why is it preferable to lower the transfer case rather than use axle shims?

Destro

It isn't preferable, but somehow most people will do the quick and easy TC drop rather than figure out the correct angle and shim to get the angles correct.

Also the TC drop many people put in as a temp measure while they save up for a SYE. Some people just never manage to actually do the SYE...

:-)

wildbill1

Well, I changed the u-joints and I'd say the vibration is nearly gone. I checked the pinion and transfer case angles and found that they are dead even. When I used my magnetic protractor, they both read 87 degrees.

Would it be beneficial to shim the rear side of my spring perch to lower the pinion shaft? In my experience with vehicles other than Jeeps, a few degrees is where it should be. My local parts store has 4 degrees shims on the shelf.

Gee oh Dee

Were the old U-joints worn? Just curious, as I've seen tons of people with bad U-joints who think they need a t-case drop. For example the PO of my truck.

wildbill1

The old u-joints weren't real bad, but I could feel a bit of a notch where they used to ride. I think my minimal lift put them in an area where they had never run before. That might have been what was causing the majority of my vibration.

Gee oh Dee

Yeah, the previous owner of my 87 said it'd need a tcase drop, but it only has a 3" lift, so I was sure it was the U joints. Hell, its got 200k+, I figured what would it hurt to look into? Sure enough....

caged

you could, and should use both together.
the pinion should be facing the output on the t-case.
the less the angle, the better.

pickles

Not trying to thread jack. But where does a person buy axle shims?

DropPoint

had 2" lift and a little vib. changed leafs out to net ~3.5" and a lot more vibrations. totally against tc drop so i added some 4 degree shims and now its much better.

i still do have a little bit of vibrations once in a while so maybe it's my re-used ubolts. what exactly causes vibrations from old ubolts?

casualties

Old u bolts wear just like any other part. best described as slop. or wallered out. ya know? its like pulling an old bolt out and seeing the corrosion thats taken place leaving the center shank section thinner than the threads or the shank right at the bolt head. make sense?

wildbill1

What I have found is that both the transfer case and pinion shafts are at the same angle. I know this is not a bad thing, but from working on Mopar muscle cars, I seem to remember that it is preferable to have the pinion angle slightly (4 dregrees or so) lower than the angle of the transfer case/transmission shaft. Is this true with XJ's as well?

caged

this is the ideal way you want it to look.

mende21

ONLY if you installed a SYE and a CV driveshaft. If you have a stock setup with the slip yoke then the transfer case output and rear axle pinion should be nearly parallel with the pinion pointing slightly down a couple degrees.