Rear End Shims

I bought a 1999 XJ from a kid who put a skyjacker 3'' lift in it. My question is about the rear shims installed. The shims are installed with the wider part towards the rear of the vehicle and the skinny or thinner end towards the front of the vehicle. Is this correct? A driveline specialist in the area thought they were installed wrong. Any suggestions. I have a vibration from 30mph-34mph then again at 60 + mph. I haven't installed a t/c drop kit yet. ( dang broken studs!!!)
thanks

the shims sound right to me

you need to remove those studs anyways to install a transfercase drop.

-Tim

if this is the local "specialist" im scared for you

-Tim

Hard to say. If you do NOT have a SYE and CV driveshaft then in simple terms the yoke of the transfer case and the yoke of the rear diff should be on parallel angles. Vibes will most likely happen becuase the slip yoke DS can't handle the angles. Doing the drop may help quite a bit.

jeepnuts311 said:

the shims sound right to me

you need to remove those studs anyways to install a transfercase drop.

-Tim

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Glad you corrected... Flipping his shims would point that pinion up way too high.

Rocketman said:

Glad you corrected... Flipping his shims would point that pinion up way too high.

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i was thinking about it backwards at first like it was spring under.

if the wide part of the shim was towards the front, it would point the pinion down and worsen his angles.

-Tim

before i did my SYE, i had a 4.5" lift on my XJ. i had a 1" transfercase drop and 6* shim in the rear with no vibes. even though you are supposed to have the t-case output and the pinion parallel, i experimented and that is what i found that worked. i ran that for about 7 months on my DD. i also had a np242, which tends to have less vibes because it hangs lower

after i installed my SYE, i found that 6* was far too much shim and now am using 2* flavor

keep in mind that if you are using shackles for lift, like me, then you already have a little bit of "pinion up"

-Tim

No dude, NP231's on older jeeps are the Tcases that tend to have less vibes, because of how the slipe yoke is inside of a sleeve that extends from the transfercase. I'm also pretty sure that the 242 didn't really hang lower, and if it did, it is minute.

P.S. don't trust your local "specialist" anymore. The shims have the thick part towards the rear of the vehicle. This angles the pinion up towards the Tcase. It would be the other way around for Spring-Under-Axle.

begster said:

No dude, NP231's on older jeeps are the Tcases that tend to have less vibes, because of how the slipe yoke is inside of a sleeve that extends from the transfercase. I'm also pretty sure that the 242 didn't really hang lower, and if it did, it is minute.

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spobi dude.

the old style NP242 also has the internal slip yoke i have rebuilt both kinds of t-cases, they have the exact same setup. they both switched to external slip yoke in 1996.

also, the np242 hangs down about 1" more than the np231 because it is clocked differently.

-Tim

Not spobi dude, Thats just what I said, the NP231 has the internal slip yoke (aka, slip yoke in the sleeve), therefore less vibes. Almost all of the older Cherokees I have been around that I can remember have been NP231, so I was refering to those.

Yes you were right, the older NP242s did have the same type of tail housing. BUT, he is talking about his '99 Cherokee, which did not have this tail housing, therefore was prone to more vibe. (which reinforces when I said the older jeeps are less prone, and also means that the NP242 isn't less prone to vibe. How you said it you made it sound like every NP242 wasn't prone, thats not the case. My NP242 experienced its fair share of vibes)

As for the hanging down, alright, I'm sure your right, I haven't really noticed, but I'm sure its probably because since its an inch, I wasn't really paying that much attention, I have only really payed attention to my '99.

So, what I said did have truth, not bs dude. granted I should have started my comment differently.
-Mark

begster said:

Yes you were right, the older NP242s did have the same type of tail housing. BUT, he is talking about his '99 Cherokee, which did not have this tail housing, therefore was prone to more vibe. (which reinforces when I said the older jeeps are less prone, and also means that the NP242 isn't less prone to vibe. How you said it you made it sound like every NP242 wasn't prone, thats not the case. My NP242 experienced its fair share of vibes)

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but a np231 in a 99 would also have the external slip yoke and the orignial poster still has not specified which transfer case he has.

from my experience when i had a np242 i had no vibes then i swapped to a np231 and i had vibes on the same lift then i installed a sye. this was on a 4.5" RE lift which gives 5" after settlng and a 1" t case drop. i have never heard of a np231 getting away with a 4.5" lift without a sye. if you know someone that has, please let me know. this is why i did not budget for a sye from the beginning because i searched and found that with my old style np242 i could get away with 4.5" and if i had a np231 i couldnt.

nonetheless, he should install his transfer case drop and see what happens.

-Tim

edit: since we are talking about shims, i want to reiterate the point about correct shimmage being important. his PO should have searched before buying a lift expecially on a late model which, as begster stated has a external slip yoke and is very prone to vibes even at small lifts.

FYI some of the last years for XJs 00-01 had vibes from the factory and had t-case drops installed at the dealer.

Now Now you two. Thank You both for the info. I will be installing the t/c kit next week. I have been drag racing since I was 16 so I have little knowledge with XJ's. I just bought this truck a couple weeks ago as a graduation gift after 6 years of college (no I'm not going to be a Dr.). Next summer I will be going on an expedition in the backcountry of Colorado for a couple weeks.
Can't wait.
Ross

I have a np231. t/c

Jeeze guys, it's pretty simple and really doesn't matter what TC you have. I have a RE4.5+" lift on my 93. I have a 231 and a C8.25. I had a 1" drop. Still had some vibes. Installed 6* shims with the "thick part" in the BACK to correct my pinion angle so that both yokes were on the same parallel plane.

After I installed a SYE, a double cardan DS and removed the drop, I had to REVERSE it so that the thick part is in front so that my pinion points to about 2* below the angle of the TC yoke. I got lucky in that the 6* shim worked for me in both cases. I measured the angles with the angle finder and it worked out almost perfect.

Sorry, but I can't figure out WTF you two are arguing about. EVERY XJ is different. Every TC hangs at a slightly different angle. Every rear pinion sits at a slightly different angle. Those 1,2 or 3* differences add up and make a difference. You have to make the adjustments based on MEASURING YOUR RIG. Out of the factory, they may have all been the same but after 178,000 miles, they are all different.

Now, get over it!!Hasta

Rocketman said:

Jeeze guys, it's pretty simple....

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Yeah, it's not rocket science....

:laugh3:

I would have to agree with you two. Sorry.

On my '99 NP242, 4.5 i used 4* shims before and after my SYE. I just went to 5.5'', and I'm still using them.

sorry, begster and the rest of ya eace:

keepin on jeepin on

-Tim