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front axle shims?


NAXJA Forum User
I'm talking to a fellow XJ owner at work today about my 3" OME lift that I'm gonna do next week. We start talking about 1" TC drop to get rid of vibration. he say's YES, it worked for the rear end - NO, I wouldn't do it again! He explains that dropping the TC helps the rear driveshaft, but throws-off the drive angle on the front "double-Cardan" set-up and caused him accelerated wear (and $700 replacement) due to it being out of alignment.
This is because when the TC drops down at the rear; the front (TC & tranny) is still higher. This rolls the front driveshaft on a vertical axis and changes the front driveshaft angle in relation to the front axle gear housing.
My question is: IF he is right, and it seems to make sense;......will a set of axle shims work OR is there another way to bring the front axle back in line-up?
If he's just blowing smoke,....is the TC drop (on 3" or less) a permanent fix....OR do I need to spring for a SYE and consider my vibration/excessive wear problems cured?
Thanks again,
I've never heard of a front axle shim. It seems like any angle changes could be taken care of by adjusting the caster.
Also, thinking about how the drivetrain "rotates" around the motor mounts when you drop the Tcase (I think) the height increase at the front of the Tcase (if any) wouldnt be a 1:1 ratio with the drop at the rear. er, something like that (I dont use a tcase drop)
What he was telling you is that as you lower the case the front output shaft angle increases.There is no way to compensate for that.Typically the stock setup is about 4-5* down on the rear output,thus 4-5* up on the front output!
TC drop implications

I have gone thru a "search" and read about TC drops. Nobody (online) seems to be having trouble (yet?) with a change in the front driveshaft angle change. My friend had to get a new front driveshaft (that he attributes to the TC drop). He has a 99XJ with a ~3" lift and 30 x 9.5 x 15 tires. He is also quite mechanically proficient (a experimental mechanic at DaimlerChrysler),...otherwise I would not worry about what he is talking about.
I did stumble across a non-NAXJA webpage (doing a www search) that showed how different people with different lift heights get vibrations. The guy with 4" (nothing),....the guy with 1" gets them? :confused: So I guess I'll just have to cross that bridge when I come to it. ;)
Is there nothing (preventative) that I can do to equalize the front driveshaft angle after the TC drop (other than caster)? :confused:
Thanks again,
It's interesting that your friend is a tech with DaimlerChrysler, because the transfer case drop is the DC factory fix for driveline vibes in the 96 and newer XJs with Up Country.

Due to the revised ("improved," in DC double-speak) transfer case output design that was introduced in model year 1996, even the 1" lift you get with the Up Country suspension is enough to induce vibrations -- sometimes slight, often quite severe. The factory offers a t-case drop as the "fix" for this. The service writer at my dealership had the drop installed on his wife's '99 Classic and he reported that it removed "most" of the vibrations. I refused to do it on my 2000 and I have a JB Conversions SYE waiting until I can afford the new drive shaft to go with it.

A large number of people who have passed through these forums have run the drops, and I can't recall anyone ever reporting that they caused the vehicle to start eating front driveshaft joints. The shims referred to are used to adjust the caster, so you lads are all on the same page with that. Caster also affect death wobble after a lift, so there is some compromise involved in setting the caster on a lifted XJ but I would be surprised if the angle change induced by the drop would be enough to start destroying u-joints. Especially since you said he blew the double-cardan joint, and the entire purpose of a double-cardan joint is to operate through a large angularity. The transfer case drop could not increase the front shaft angle enough to exceed the operational tolerance of the double cardan unit. I think there was something else wrong with his Jeep.
Front shims go behind the lower control arms and set the caster angle (Adjustable arms do the same thing) I guess they would also rotate the front pinion while doing the caster job, tho kind of in opposing directions. In a 'perfect double-cardan world' the pinion points at the output. This won't happen on an XJ (especialy a new XJ with low-pinion 30) unless the steering knucks get cut off the tubes & rotated.
TC drop implications

I'm gonna put the sucker in and run it! I may try 1/2" drop 1st,....and if that doesn't clear it up....then go to 1" drop. My buddy musta busted or tweaked something else while wheelin' ;) . I'll shoot some before and after pics when I'm finished with the lift installation (hopefully this week).
Thanks again,