Four Wheeler - - Techline -

QI have a drive­shaft ques­tion that I have re­ceived dif­fer­ent an­swers on. I have a ’97 Jeep XJ Cherokee with about 4 inches of lift. I can feel a vi­bra­tion start­ing at like 59 mph and it gets worse the faster I drive. I can take my rear drive­shaft out, driv­ing in four-wheel drive (front axle only), and the vi­bra­tion goes away. I’ve had the drive­shaft re­built. It turns out that they used a smaller U-joint, so I went back and got the cor­rect U-joint, but the vi­bra­tion re­mains. Should the pin­ion of the fac­tory Chrysler 8.25-inch rear dif­fer­en­tial be pointed at the NV231 trans­fer case, or should it be on the same de­gree plane as the trans­fer case out­put? I’m not sure how to find the de­gree at the axle and trans­fer case. The videos I have seen never re­ally tell you where to put the de­gree finder or what the an­gle should be.

I know my trans­fer case is at 0 de­grees. I have a 1-inch trans­fer case drop. I put 4-de­gree shims in the rear leaf packs to bring the pin­ion back down, but then I was told that I should point the axle pin­ion at the trans­fer case. I’m try­ing to keep it cheap for now, what are my op­tions?


AIt sounds like you have suc­cess­fully iso­lated the vi­bra­tion to the rear of the Jeep. Con­sid­er­ing your setup, I think it’s safe to say that the vi­bra­tion prob­lem is in the rear drive­shaft. Typ­i­cally, any lift over about 2 inches or so will cause at least some vi­bra­tion to em­anate from the stock XJ rear drive­shaft. With your lift and trans­fer case drop, you’re at about 3 inches of lift over stock as far as the rear drive­shaft is con­cerned, which is not an ideal setup. The vi­bra­tion can even­tu­ally lead to a leaky trans­fer case rear out­put shaft seal, worn out­put shaft splines, and in some ex­treme sit­u­a­tions, com­plete trans­fer case fail­ure. The best way to cor­rect the vi­bra­tion is to in­stall a slip-yoke elim­i­na­tor kit on your trans­fer case and add an af­ter­mar­ket dou­ble-car­dan drive­shaft. On the plus side, you’ll be able to re­move the T-case drop and pick up ex­tra ground clear­ance.

If you are on a bud­get and want to ex­per­i­ment with what you have, you may be able to de­crease or pos­si­bly elim­i­nate the driv­e­line vi­bra­tion with some care­ful mea­sur­ing and pin­ion an­gle ad­just­ment. To do this, you’ll need equal an­gles on the up­per and lower U-joints of the rear drive­shaft. This can be mea­sured with an an­gle finder on the flat ma­chined por­tion of the yokes. If the trans­fer case yoke is at 0 de­grees, the rear axle yoke should be at 0 de­grees too, or neg­a­tive 1-2 de­grees to com­pen­sate for axlewrap un­der load. Tapered pin­ion an­gle shims can be in­stalled be­tween the leaf springs and the leaf spring perches on the axle to al­ter the pin­ion an­gle. How­ever, if you go this route, you’ll need to care­fully cy­cle the sus­pen­sion at full droop to see if the drive­shaft binds. If it does, you may be able to clear­ance the yokes a lit­tle with a grinder and/or in­stall sus­pen­sion lim­it­ing straps.

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