NP231 Output shaft angles

I've been fighting vibrations when the front driveshaft is connected for a while now. I've rotated my front axle anywhere from about 6* caster to -1* caster (I think that was about 9* pinion angle) on my D30 with a sweet spot around 3* caster. I still hate the steering with that little caster but I don't want to go through the effort of rotating my C's until I can be sure I can get the right pinion angle figured out or use this as an excuse to find a 44 (almost impossible around here for some reason) with high steer that I can fab up to make fit.

My question is, are the output shafts from the NP231 supposed to be level with the ground? I checked the angle on the front and its pointing about 8* up and I suspect that's why I can't find a vibe free angle on the pinion since it will always be trying to bind the cv joint.

I haven't rebuilt the front shaft yet but it's solid when I try to move it and I put it in place of the rear with nothing up front and it was as quiet as the brand new rear I have. I also ran the rear DS up front and get the same vibes. At 6* caster, its bone shaking and about 94 decibels in the cab and right now at 3*, it still vibrates enough to make conversation almost impossible and still 89 db.

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91 XJ, 4.5" lift, 33" MT Deegan 38's, SYE, NP231, AW4

Whats your trans mount look like? Ive found they can sag and cause vibes. May not be the end all solution but something to look into. Also, what is the angle of your front shaft in relation to the output?

I'm suspecting the transmission mount is bad and hoping that it will raise everything up and level out the output shafts. I had the DS and pinion at a straight line (about 9* I think) and it was no better than where I am now with the pinion below the DS some. That's why I want to know if the output shaft of the transfer case is supposed to be clocked up in front. That will help me determine if I want to go through the hassle of changing the engine and transfer mounts. Transfer mount is easy but engine is more work and I don't want to do one without the other.

Is there a TC drop on your XJ? If the TC is dropped to facilitate the rear drive shaft, that drop will cause to front of the TC go up the way you described it,...unless the transmission mount is that bad :dunno: .

No drop since I have an SYE. I'll pick up a transmission mount tonight while I'm out and hope it works. The Rough Country cross member is irritating me too but I doubt it's dropping things too much. I want to reinforce the frame now that I have a welder in house and will need to build a crossmember too since I don't think that three piece RC cross member will work with reinforcement.

Replacing it with a new mount brought the angle down to 4* above horizontal and didn't change my vibes at all. I may shim the mount a bit since the studs are at least twice as long as the OE mount and see if I can get it to 0. Right now, the front DS and pinion angles are identical at 8* but I noticed one of the lock rings on the cv side of the shaft is half out. I'm rebuilding it anyway but maybe there was some looseness in there that I couldn't feel when checking for it by hand.