After reading this post, I'm inclined to agree with under dawg. On my ZJ, I was never concerned about castor, but concentrated on getting the pinion angle perfect with the shaft angle. Once I did, the vibration was minimized. After the 6" lift on it, I have no idea what the castor angle is, but it drives straight with no bump steer, DW, or flighty handling. My JK castor is at 4.8 degrees by my angle finder and the alignment print out. The pinion angle, however, is off by a few degrees. From what I've read here, I'm going to shorten the lowers to get the pinion angle correct and see how it drives. Maybe I've got one of those JKs that will drive fine at 3 degrees castor.

 

I've always maintained that it isn't one single element that has contributed to the failure. If you all read through the entire post my opinion (because I am not a Engineer by trade or training and don't work for Chrysler's design team) was that there is poor material (see Ken1010 post) and IMO the design of the casing looked different between the two I've had COMBINED with the other things like gearing, lift (angles, caster, pinion) contributed to the failure. My opinion was there was little margin for error as a result of the poor material in the casting and the design (they may be the same casting but mine looked to be different).

So to say that because the stock JK's are blowing up there t-case alone shows there is no correlation in my opinion is missing the overall "no margin for error" portion because they aren't modified with the other things like gearing, lift (angles, caster, pinion) which are needed to close the gap and contribute to the failure.

Agree. In my earlier statement I said my caster was 7 but I couldn't tell you that I was on level ground when taking the measurement and I didn't do as you said and take multiple readings. Mine was one measurement while I was under the jeep torquing down bolts. However, when the dealer replaced my t-case they did do their own root cause analysis to determine the failure and one of those things was to check caster and pinion angles and the said they'd report if they saw that as a problem. As I stated earlier, their opinion was that the damage was caused by the "excess" droop that the coil overs get allowing the HD DS to make contact with the transmission skid (auto), which I've notched several times, resulting in the DS being shoved into the t-case causing the damage. I know crazy talk but that was there findings and since they had already covered the t-case under warranty I didn't argue it.

Edit:
About 2 weeks prior to the t-case failure I had the front DS checked out and balanced. It really didn't need balancing I wanted it to be looked at since I noticed it had some contact hits against the transmission skid plate.

Agree 100%
IMO That's why we aren't seeing the failure on the stock JK's.

 

What may also be relavent is how many of the exploded T-cases were running the OE type flange adapter double carden ds and how many are running coilovers. I was running a jereel OE replacement shaft, seemed fine until I got 5.13's installed(on 35's at the time), then it started squalling at 40mph, vibes at 65-70. Dealer rebuilt the T-case, couldn't find anything wrong, blamed the noise on my auto locker causing the tfcase chain to rattle Still had same noise after, just not as bad. Had TFcase totally replaced, noise even less, still jereel(just a new longer one), same castor, still 35's. Put 37's on, noise almost completely gone still vibes though, changed to TeraFlex shaft w/yokes, noise gone completely, although I do have a slight vibe at 55mph, seems to go away after 60mph. Changed castor, vibe didn't change any, so I'm gonna take the ds for a re-balance. Anyhow, thats my tcase/ds saga abbreviated version. My jk was down 3mos with various shops trying to track the noise and vibes down.
Oh, I should add, I sent the original jereel back and it was balanced perfect, they couldn't find anything wrong, they sent me a new longer one cause the first was abit too short for the amount of lift I had. Jim Reel said at the time (over a year ago) that I should go with the yokes on 5in of lift, they'd already had a couple of blown tcases on 4in or more of lift that people were blaming the OE flange double cardens on. So, there are prolly more blown tcases out there than people think. Some people aren't on forums as much , if at all that have modded jeeps.

 

After reading this post, I decided to pull my front DS - easy enough to do, plus got to spend some time getting greasy.

Drove to the gym and am again wishful for a vibration solution. Though mine is very mild at 40-45 mph with 5.13s and 35s, I may once again try a lower castor. I am between 4 and 4.5 now. Using simple angle finder. I have been up and down and back again with the lower control arm adjustments...I got between 4 and 5 inches of lift with the Teraflex 3 inch kit. I have full control arms, so plenty of adjustment.

With the front DS removed, I'll save the adjustments for the fall.

Part of the fun I guess. I have the Jeep of my dreams, but am dealing with vibes and some mild whine from my rear gears. Got to pay to play...

 

Your gears shouldn't whine.

 

Hey i know, and the guy that did the install is more than willing to take a look at them. Something comes up every time I try to get in to have them take a listen. The mildest of whine when I lift off the accelerator.

I was really hoping to move up to 37s and add a 1 inch BL when the 35s are replaced, but maybe I'm maxed on how much the JK can stand and still stay breakage free :(