I am at my local shop and they refuse to set my caster to 5.5. Says they just recently did it to a jeep and it destroyed his gear box. I have 4 inches of lift and adjustable lowers. He claims I need a new gearbox or spacers. Otherwise all adjustable arms to push axel forward. From what I've read I should have caster around 6 but have also read on hear it leads to bad driveline vibes n gearbox issues. How would one go about getting 6 degrees of caster safely?

 

Here is the spec for JK caster: CASTER + 4.2° ± 0.5° (+3.7° to +4.7°)

Wondering why you want more.

Even at the factory spec, you may have too much pinion/drive shaft angle, especially if you have an after market drive shaft.
This can cause the transfer case to fail if it gets to vibrating.

 

From all I've read it increases handling? Its in the faqs on suspension.

 

Yes, it will increase the tendency for it to return to straight ahead, and stay there.

Unfortunately, it's contrary to what the pinion needs after a lift.

All you can do for now is compromise between the two, (caster and pinion/drive shaft angle), and see how it handles, and if it vibrates at highway speed.

 

suppose ill stick with what its at and look at some other options to fix some handling. Its really not to bad the new tires ride alot better.

 

ronjenx is correct regarding a stock D44 which has a pinion angle of 6 degrees. On a stock jeep with 4.2 castor, the pinon angle is 1.8 degrees which is fine for alignment with tcase. On a lifted Jeep drive shaft angle increases and if more castor is done the pinion angle will be reduced to the trouble point. This is the dilemma ronjex is describing and illustrates the challenges in using stock axles with bigger lifts.

If you want to solve this long term you probably will need to go with an aftermarket axle such as the ProRock 44 Unlimited which has a pinion angle of 10 degrees and will enable castor of 5.5 - 6 and still have the pinon angle twice stock at 4 degrees towards the tcase. This works super well and is what I've done. Best of both worlds, sufficient castor for the lift and better drive shaft angles as well. Of course it is pricey like most other big lift mods.

You could also move the axle forward a little with adjustable upper and lower control arms but that gives just a little relief.

Good luck with your build.

 

As others have clearly stated, 5-6* of caster is far too much for a stock housing. The resulting pinion angle can have a dramatic effect on the drive shaft and transfer case. Over all, 5-6* is a great caster angle and we usually build in that and more into our builds. The added caster of our PR44 Unlimited has really made a huge improvement in the driveability of a lifted JK.