I have a 4" lift and I'm unsure if my pinion angles are correct for my lift front and rear. Any rule of thump or easy way to tell if I'm off a lot or a little?

 

If you go out to Tom Woods driveshaft website, you will find a lot of information on the correct angles. Don't recall if it is in the JK section, or the tech info area, but you will find some diagrams for both types of driveshaft.

And if you go up to the writeups area and click the index at the top, you can find a DIY alignment writeup that will give some info on checking the caster angle. (though I think it needs to be updated on where to put the angle gauge?)

 

Angle finder. The full circle one with a magnetic bottom....

 

Here's a good (though somewhat dated) Tom Wood article to get you started:
http://www.4xshaft.com/JR7_TW_Driveshaft.pdf

Actually, the stock pinion on a JK FRONT axle is supposed to angle up 2 degrees when the caster is factory recommended 4.6 . The circles on the front of MY front axles are perfectly vertical when my caster is 4.5+/- degrees. That is what mine looks like anyway. Your mileage may vary.

To be honest, those magnetic angle indicators that sell for under $20 are hard as heck to read and never accurate to better than 1/2 a degree. I set mine on a level surface and turned it 180 degrees and read it again. My 90/zero was off -0.75 (eye-balled) degrees. I use my cell-camera to photo the reading face-on so I can zoom later. Also consider the fact that the ground is not perfectly level. I thought my garage floor was level but after measuring it I found it slopes 0.5 degrees. That 0.5 degrees had go into my reading corrections.

Probably the best way to measure slopes is with a laser on a level. You can shoot the laser against a flat surface several feet away then use a tape measure and a little trig to get much better accuracy.

The front angle is a trade-off between pinion angle and caster. The rear pinion angle should always be set to line-up with the driveshaft.

This all assumes you have a CV or double cardan at the transfer case and a single cardan (U-joint) at the differential.

 

if you know its off account for it. also if the ground isnt level it wont matter as your measuring the angle in the rear to be the same ground has no effect. in the front how about put it on the ground first then go from there? It will deffinately be plenty to get you close enough.

 

Let me do some reading first and I'll post back. I don't know anything about it. Y'all are recommending things I have no idea about haha.

I will say this both my front and rear( if I remember correctly) are almost flat. When looking at the top ball joint vs the bottom ball joint they don't line up. The top one is more toward the rear of the vehicle. This is what sparks my interest. If the pinion angle is too low, I'm killing the driveshaft. Loosing ds clearance and probably making my ride suffer as well

 

I still have factory shafts which are the cv. Also. I'll have to check the rear for the angles of both. I know my rear springs have a nice small bow in them(with correction plates) and the front have a little less than the rears do.