After installing a 2-inch suspension lift on our '97 Wrangler, we immediately began to experience an aggravating rear driveshaft vibration during medium to heavy acceleration. It reminded us of those quarter-operated vibrating beds you find in cheap hotels (not that we'd know). Since our Wrangler is neither quarter-operated nor cheap, we set out to eliminate the problem.
Rear driveline vibration is common in lifted Wranglers because of the short length of the stock rear driveshaft. The short shaft is a byproduct of a couple of key things inherent to the TJ Wrangler. First off, the TJ has a short wheelbase; hence, the distance between the transfer case and the rear diff is short. The second factor is the slip-yoke output shaft on the NP231 transfer case. Since all of the driveshaft's travel occurs at this point, it naturally requires a long-output shaft, thus a shorter driveshaft. When you add a suspension lift to your TJ, the increased U-joint angles create driveshaft vibration, which is not only aggravating but hard on driveline components. There are a couple of ways to solve the problem. You can stretch the entire vehicle and add a longer driveshaft (difficult), or you can install Tom Wood's new slip-yoke eliminator kit (easy).
We installed Tom Wood's Custom Drive Shafts new Slip-Yoke Eliminator kit for the late-model '96-and-newer NP231 transfer case in a little less than four hours, including photo time and a taco break. Buddy Dederich, head technician at J&L 4Wheel Drive Center in Sun Prairie, Wisconsin, took care of the install. We used a vehicle hoist, but the kit is easily installed with the vehicle on jackstands or with the transfer case removed from the vehicle. All of Tom Wood's driveshafts are custom-made for your specific application, so we just followed the directions on the Web site and called him with the yoke-to-yoke measurement. Wood says that almost all orders are shipped within 24 hours after the order is placed, and ours was no exception. The kit contained a new output shaft, a seal, and a complete, ready-to-bolt-in heavy-duty CV driveshaft.
Once the kit had been installed, the annoying motel bed vibration was gone, and we gained a rear driveshaft that was significantly stouter than the stock unit.