The NP231 with its slip-yoke is the culprit. Even with kits that come with tapered blocks, driveline vibration in some shape or form is inevitable. You do have options to cure this problem.
You could go and purchase the slip-yoke eliminator, which means you have to buy a new driveshaft, which means you have to have a custom length made, and balancing, and installation, and with all of that…BIG BUCKS!
For the working man on a budget, however, the next best alternative is to drop the t-case. In this installation, we have selected a Rubicon Express 1/2 inch drop.
At first glance, the kit looks easier to install than assembling a two-piece pool cue, but looks can be deceiving, and here’s why. The factory mounting bolts for the t-case support are a combination of a bolt and a stud-n-nut on each end. And the question that always pops up is, “How the heck do I get the stud out?!” Rubicon Express recommends two ways.
After placing wheel chocks under the front and rear tires, position a hydraulic jack under the t-case cross member with just enough pressure to hold it in place so you can remove the mounting hardware. So far so good? Okay, here’s the tricky part. Using a double nut technique, you can back the stud out.
Make sure you use plenty of spray lubricant beforehand and even heat the stud with a torch (when working with flames, be sure not to get near any fuel lines) to loosen the Loctite when the stud was installed. This may work in some cases but I’ve found a much simpler way to extract the stud.
Remove the nut from the stud on one side. Be sure to leave in the cross member bolt on the same side. Get yourself a good hacksaw with a good carbon steel blade (don’t be cheap on the blade or you’ll end up wearing yourself out trying to cut). Cut the stud as flush with the cross member as possible.
Once you cut the stud, center punch it. Then with a decent high-torque drill, use a 1/16th inch drill bit (made for steel) to drill out the center (be careful not to apply to much force or you may snap the bit). Drill into the stud about 3/4 inch deep. Change drill bits and keep redrilling until you have finished up with a 1/4 inch drill bit.
Get yourself a tapper and a 1/4 inch screw remover (or Easy-out). Add an extension to the tapper handle for leverage and wrench that stud out of there. You did it! The stud should start to come out. Once the stud is on it’s way out, simply remove the bolt on the same side. Then, slowly drop that side of the cross member.
Remove the stud completely. Add your spacers and new bolts and tighten them according to the proper torque specifications.
Simply repeat the procedure for the opposite side of the cross member (remember to reposition the hydraulic jack) and soon you’ll be on your way to your favorite trail…vibration free!