XJ DRIVELINE VIBES
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?
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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.