I've been doing some research on the subject. My understanding is this.
In order to have a smooth drive line the center line of the output shaft and the pinion shaft need to be parallel and the driveshaft slope needs to be less than 30 degrees.
I installed a 2" BDS lift. The kit came with a TC drop kit that lowered the skid plate about 1.75" but no axle shims. So, my output shaft and pinion are no longer parallel. I now have a vibration in my drive line.
I'm wondering if I really need the TC drop with a 2" lift.
Is anybody running a 2" lift without a TC drop?
If so, Are you having any issues?
I'm going through the same thing right now. Go to Quadratec.com. look under their Knowledge section. There is a great write up.
I tried to install shims but found the left side shock mount bound against the shock body. NFG so i removed them. Back to square one.
I bought an ANGLE FINDER at Lowes, $8.99.
to find the drive angle on the pinion, look at the back of the dif. On either side of the cover you will find a round flat machined disc a little bigger than a quarter. It is hollow in the center. It is exactly 90* from the pinion angle. Place the angle finder tool against it and take your reading.
Now for the t case: put the jeep in nuetral. CAREFULLY move the jeep forward or back until the slip yoke's flat machined surface (where the U joint is) is horizontal. Block the wheels there. You can then use the angle finder to measure the t case angle.
Thats what I have done. I have now began to build my own t case drop kit. The issue I am having is that I can find longer bolts with the special angled flange head. I'm currently trying to machine a bushing down to act as an thick angled washer which will replace the angled part of the bolt head. Fun Fun Fun.
All together I think I will need about 3/4" of t case drop. You might need a little more or a little less. I'll keep you posted as I work through it on my own thread.
Oh, I forgot, I am running a 2" lift with 2" shackles for a total of 3" of lift. I just removed the lifting shackle in the rear and that got me closer for the mean time. Once the t case drop is completed, I'll put them back.