olyelr

Ok, I have lots of researching done on this and think I finally have it figured out. Just would like to make sure...

The JK front axle has 6 degrees of separation between the caster and pinion angle, with the pinion up 2 degrees and the caster at 4. According to a post I read from Dynatrac, one of the most accurate places to measure is at the pinion flange as there can be differences in the castings on the C's. I also read that placing the angle finder on top of the ball joint will give an accurate reading of the caster... True?

I just installed a 3.5" RK X-factor lift. I have the control arms set at what their starting recommendations are. It seams to drive pretty darn good, but I would like to measure the caster anyway to assure I am close. So really all I have to do is make sure the pinion flange is angled up 2 degrees, which would make my caster at 4 degrees? It sounds like a little more caster would be better, but that will make the pinion angle worse which is not really a good idea either.

Any insight will be greatly appreciated.

Sahara Lee

Here's a thread where caster was discussed.
https://www.jk-forum.com/forums/modi...t-help-287317/

Check the WayOfLife link for more useful information.

Also, there is an app called Clinometer that works amazing for measuring angles with a smart phone. Great resolution with a digital readout that you can freeze so it can be read once you climb out from under the vehicle.
Clinometer | plaincode

I use the free Android version.

ronjenx

Your best option is to get an alignment check and make note of the caster. Then see if they will let you reach in with your angle finder and place it on the end of the pinion housing. Make note of that reading. That will give you the true difference in angles for your specific axle housing. From then on, you can park on a level surface, and with a little math you can figure your caster.

olyelr

Thanks for the link and call-out for the WAYOLIFE link (although I have read them both). Much appreciated!

So you are saying the separation between caster and pinion angle could be different between JK axles? I suppose it could be slightly, but surely not much.

I have an angle finder, and if I put it on the pinion flange that will tell me the degree of that (as long as the Jeep is on perfectly flat ground). From my research, the caster is 6 degrees different (although I suppose that can be slightly different for each axle).

Is it safe to just put the angle finder on top of the upper ball joint for measuring caster?

ronjenx

It depends on if you want a ball park guess, or a reasonably accurate reading.
If you want to know the caster angle, it has to be measured on the alignment machine. There is no other way to know for sure unless you take the knuckle and ball joints off, put a king pin down through the top and bottom C's, and measure the angle of the pin.
Things like the top of the ball joint, on top of the C, or any other part of the axle housing, all represent variables.

You can buy tools to measure the caster at home, but it will be a similar method as that used on the commercial alignment machines.

Once you know the caster reading, you can use any part of the axle you want to make a comparison. As long as you use the same point each time you check, a little math will tell you the caster angle.

olyelr

Exactly. From what I understand, the stock JK axle is set at 4 degrees caster and the pinion is up 2 degrees (actually, 4.2 caster and 1.8 pinion). That's 6 degrees of separation. Measuring the angle of the pinion flange is pretty fool proof.

So, the way I look at it is if my pinion is at 2 degrees then the caster should still be 4 degrees (if that is in fact the factory setting). If the pinion is at 4, then the caster is at 2. If the pinion is at 1 then caster is 5. I just need to make sure the Jeep is on perfectly level ground (or figure out how many degrees the ground is sloped and factor that in).

olyelr

Well, I did some closer checking on flat/level ground with a degree finder and I figured the pinion angle was set right around 4 degrees after the lift was installed. By my calculations that would have made the caster at 2 degrees (6 degree separation between the two from the factory). The Jeep drove a bit flighty like this, as to be expected, but honestly it was not a whole lot worse than stock was (I wish I would have gotten an alignment when it was stock for shits and giggles - It was quite a battle to keep the Jeep between the white lines if there was any bit of wind, even when it was 100% stock).

Anyway, I shortened the uppers a bit and got the pinion angle right around 2-2.5 degrees. So now the caster should be more around 3.5-4 degrees. The Jeep now drives great. Better than factory. Straight as an arrow with no drama.

I still think I should get the alignment checked professionally just to see how close I am with my guestimations. But, it does drive great and there are no vibes, so I guess I really don't care where the caster is at... just a curiosity really.

Mark Doiron

That doesn't sound right. The only adjustments stock are toe and steering wheel centering. If you have flighty steering stock, something may be bent. Anyway, glad you're happy with it now.

olyelr

Thanks. Yeah it seems to drive probably a good deal better than it did when stock. I bought the Jeep brand new, so I something is bent it came that way because I sure as heck havnt abused it by any means. When installing the lift everything seamed good... no cracked welds or bent mounts or anything like that.

Its not like the steering was necessarily "flighty" per say when it was stock, it was just a chore to keep it between the lines when it was windy. It very well may still be that way (havnt driven in winds yet since lift), and these Jeeps may very well have that characteristic... I don't know cause this is my first JK.

ronjenx

My stock JK keeps me busy on the wheel with a good cross wind, but I wouldn't say it's a chore to keep it between the lines. Yours being lifted is bound to be a little less stable than stock.