newb caster questions.

I took my jeep to get it aligned and the tech said he could not adjust caster. I was in a hurry so i just picked it up and took it home to mess with it myself.
The jeep actually drives straight,
i checked toe in using stock wheels with no tires, I wired a 4' level to each wheel and leveled them, I measured my tires (34" i think) so i made a mark 17" on each side of center of hub. at 17" forward of center the levels were 3/16" closer than they were 17" aft of center line. this tells me i had 3/16 toe in and everything i read says anything between 1/8 and 1/4 is a good starting point.
However when checking for caster I can not get the same reading in any one spot. top of knuckles say -2* bottom of knuckles dont coinside with each other and i can never get the same reading more than once. the top of the d30 housing is giving me around 8* + and the bottom of the diff cover is reading 10* +
I got this 30 used and have no idea if knuckles were turned, (I assume they have not been as they look factory)

The issue: at highway speed the steering is very sensitive and touchy.
from what i read this is directly related to caster. I have virtually no bump steer and the jeep barely pulls to the right, I can easily live with this. I can not live with white line to yellow line like im trying to get on 2 wheels.

The jeep has a 6.5" lift IRO long arms 35" mtr's. so the guy telling me caster can not be adjusted obviously didnt care enough to look at the caster adjuster.
I took it back to the alignment shop today and they guys only help was that jeeps with big tires are going to drive bad, I offered to pay for another alignment if he would get it right to no avail.

all the steering has 3/4" ruffstuff heims and 1.5" dom. frame has been plated around steering box. ball joints and wheel bearings are new. tires are new. everything on this jeep has about 200 miles on it. Im not going to settle for the idea that "jeeps with big tires just drive bad"

Adjust it yourself. Paying someone to do an alignment on a lift you installed yourself is a total waste of money. You already have the tools and technology, why not go the extra couple of steps?

There are lots of threads here on adjusting Caster, Camber, and Toe, I would recommend a search to get a well informed picture.

In General, Caster on a lifted vehicle is going to be a case of making Lemonaid out of Lemons.

When you adjust Caster, the Axle will rotate because that is how you adjust Caster on a solid axle vehicle.

When you adjust for best Caster with the adjuster link(s), you will adjust your front driveshaft to pinion orientation.

The FSM calls for 0 angle difference between the front pinion and the drive shaft, but that is for a STOCK vehicle.

Most folks with a LIFTED vehicle, like yours, opt for 2-3 degrees pinion down orientation as a tradeoff to get the best Caster value they can get.

You can also use aftermarket Upper Ball Joints to rotate the knuckles forward or back to change the Caster a few degrees.

IIRC http://go.jeep-xj.info/ had a write-up on using various flange parts on the axle to equate to a particular Caster angle.
You can also use an angle finder (available at most any hardware store), and measure it direct off the knuckle if you so choose.

It's never going to be stock perfect, but adjusting Caster closer to stock will get you a more derivable vehicle.

HTH
-Ron

Thanks Ron, basically my only question is exactly where to check it. I plan to do it myself, I figured a shop with proper equipment could do better than I but I guess I was wrong

The larger your tires, the more toe-in you should have. The tires tend to run straight ahead and if there is any slack in your steering or axle, your actual toe-in is less than what you measured or set in your driveway.

Pinion angle is more important than caster angle. I set my front pinion angle to achieve the fewest front drive line vibes and simply accept whatever the caster is at. IDK what the actual caster is, I never have measured it.

You may want to, or need to, run more caster and remove the front drive shaft when not being used, or to use adjustable ball joints to dial in more caster.

There should be 0 slack in my steering.
I'm running a doubler so my front drive shaft is a bit longer than stock, I'm hoping this will allow me to run the correct caster and still avoid vibes

As you mentioned, the sensitive steering is directly related to castor. When I did my drop brackets, my castor was at 1.2 degrees after install the jeep had a mind of its own on the highway. It would wander and drift everywhere. I threw in some adjustable uppers and dialed them in until I started to get vibes, then back a few turns. After a castor re-sweep, mine now reads 9.4. WELL above factory spec, and it drives straight as an arrow. I also like the added feedback in turns. I have a transfer case drop, as well as
SYE, and high pinion D30. All play a roll in my front pinion angle. Sitting at 5.5" of lift.

Top of knuckles were around 2 I got them to 4* and it made a world of difference and still no d's binding. I'm going to try it a bit more in the morning and see how far I can go.
Thanks for the help

alignment shop was open this morning and they got it

What were the final readings?

Caster ended up 5* (still don't know where there getting this reading) after adjusting caster he said toe would be off so he re adjusted that and got it back to 3/16"toe in. Drives so much better than before. Just what I expected I knew it wasn't going to be a Cadillac but what I was dealing with before simply wasn't acceptable

They get their reading based off of triangulation between the sensors mounted on the wheels. Essentially it's the degree if the line going straight through your upper and lower balljoints when compared to vertical 90 (zero). 5 degrees should be just fine.