If I rotate the front end upward so that the pinion points more towards the transfer case, and is more in line with the drive shaft, is that putting more...or less... caster in the front end??
I recently had a four wheel alignment done on my jeep and had every thing within spec. Yesterday I installed my new driveshafts and I have a little bit of vibration that was not there before. I am thinking about adjusting the front arms to rotate the pinion up and make it the same angle as the shaft.

 

If you rotate the axle forward, I believe you would be adding more caster. What setting are you currently at?

 

Raising caster:
shorten the uppers - tilts the top of the axle back
lengthen the lowers - tilts the bottom of the axle forward
Both will tilt the pinion down, increasing caster.

To rotate your pinion up to be in-line with the tcase, you will lengthen the uppers or shorten the lowers. Or a little of both

 

correct
don't go less it will make the steering flighty. try more first

 

I think he was wanting to rotate forward to decrease pinion angle, so he can't try more castor first.

 

The link below will explain castor angle and general front end allignment. With that said increasing your castor angle will improve your pinion angle. There is a comprimise between castor and pinion angles though. As you have noticed if you set your castor to factory settings (+4.2 degrees) you will have a poor pinion angle. If you set your front pinion angle correctly your castor will be bad enough to create a steering problem. A compromise between the 2 is what most are doing. I run 7 degrees castor and deal with slight driveline vibration.

http://project-jk.com/jeep-jk-write-...-end-alignment

 

Are you sure of that?

 

if you have driveline vibrations at any level you are sitting on a time bomb.

 

So, is that +7 degrees castor? And does that point the pinion more upwards towards the transfer case?

 

No, that is '+7 degrees' as shown on the angle finder you put under the C's. It may equal 7 degrees as shown on an alignment rack, but don't count on it, as the angle finder measures straight lines and the rack measures an arc of some type.

The angle finder measurement is just an easy way to get you in the ballpark and let's you make sure that both sides are the same.

Try this one also
http://www.trailduty.com/temp/pinion_angle.pdf



Depends. Put the angle finder on the c's and see where you are.

Raising the pinion angle = lowering the caster = flightier steering

You have to find some balance between flightyness and driveline vibes that you can live with...