Rednroll

Like the title says. How do you measure your front pinion angle? What is the range of that angle which is typically ok? I've read where some have used an app on their phone to get a measurement. I have no clue where to start on taking a measurement and don't understand where that angle is being referenced from but would like to learn.

TIA

14Sport

This is caster...


Caster is how much off from vertical the Cs are (or how many degrees off from horizontal which would be the same). The diagram shows positive caster. I drew the red line to show why it is 6°. Pinion is how far off from vertical the pinion flange is. There is 6° of separation between the pinion angle and the caster angle. In other words, if caster is 4.2° then pinion is 1.8°. So you can measure your pinion angle at the pumpkin (easier to get to) and then subtract that from 6 to get your caster angle. I used a simple magnetic angle finder but there's an app for that. If it has zeroing capability then zero it first on the ground to account for the slope of the driveway. If it doesn't you will have to adjust the reading accordingly. I used the spot on the differential where you would normally attach a case spreader as a flat surface for the angle finder. This is not my picture but is where I measured mine...



Should be pretty close I would think. You could also measure caster and subtract that from 6 to get the pinion.


I do have pictures of the rear though.

Pinion...




Transfer case...

Rednroll

Thank you 14Sport!!!

I'm definitely going to have to read through that a few times and chew on it for awhile, but by far that is the best explanation I have read so far. As well, it seems to show how to take the measurement without taking your drive-shaft off. I kept watching how to videos and they all were showing you need to pull the drive shaft to get the measurements and I kept thinking that sounded like a lot of work, just to take a measurement.

I kept reading how [Pinion Angle + Caster] always added up to 6 degrees, but it just never made any sense to me as to why that was the case. With your diagrams that makes a lot more sense now.

In regards to the app, I'm trying to understand where they're placing their phone as it would relate to the JK and why.
https://www.youtube.com/watch?v=OaVj6PtRewE

kjeeper10

Pinion angle is the angle of the pinion in relation to the ground (in the front)
Caster is the angle the knuckle/ball joints are set at.

At 0° pinion angle the knuckles are welded at 6° or 6° caster

Stock pinion is around 2° or 4° caster
Pinion angle at 1° = 5° caster
Pinion at 0 = 6° caster
Pinion at 3° = 3° caster
Pinion at 4° = 2° caster and so on for a total of 6°

Rear pinion angle is the differential in relation to the driveshaft. Ideally you want the pinion 0 (inline) to -2° degrees below the shaft.
Not as critical running the stock DS. Very critical running a aftermarket double carden DS.

Rednroll

I keep beating myself up over my current caster. It feels ok driving (no shakes and drives straight), but I don't think it feels quite right. However, that could be my imagination as well. So I really want to adjust my adjustable LCA's to increase the caster and figured I could take my own measurements to put myself in the ballpark (4* caster) of where I want to be after making the adjustments.

Below is my current alignment and this is with about 2.5" of lift in the front after it's been weighed down with a steel bumper and winch. I adjusted my LCA's so they were 3/16in longer than stock when these alignment measurements were taken with the bumper and winch.

I'm going to move to 35's very shortly, currently have 32in stock tires. Wouldn't the increased height of the tires lower my caster angle further?


I keep tossing around the idea of adding geo brackets in addition to the adjustable LCA's as well.

PsychoCupcake

Just a rough swag off the top of my head... 3/16" longer on your lower control arms isn't going to be enough to get caster where you want it. With uppers being held constant, you probably want to be around 7/16" more than stock. Give that a try, measure pinion angle, and go from there.

Personally, I would not add geometry correction brackets to adjustable arms. Either run your stock arms and the brackets or adjustable arms and no brackets. Don't do both.

14Sport

While putting the angle finder on the bolt heads may lose a tiny bit of accuracy, I would be surprised if it was not within the level of accuracy of the gauge itself.

From what I've read factory is 4.2° caster. It also seems to me that most guys are running closer to 5° after lifting to get a quality ride but it varies by vehicle. I'm running 4.5° with my 2.5" lift and 35s without issue. Caster and pinion are a trade-off. But IMO caster is the priority since it affects ride quality over longevity. With adjustable control arms you have the option to try different settings and see what works best for you.

Increasing tire size will not change caster. That will just add ride height without changing the angles.

You don't need to run correction brackets with adjustable control arms but some guys have. I believe Ken (kjeeper10) has at one point.

And measuring the angle off from a horizontal surface will be the same as measuring it from a vertical surface as long as the surfaces are at right angles.

kjeeper10

Yea you can try 5-5.5 caster with only 2.5" of lift.

kjeeper10

Fwiw i prefer reading pinion right of the flange. Just seems more accurate.

Since you know what your caster angle reads (2.5-3°) increase pinion by 2-2.5° to = 5° and you're all set.

14Sport

I agree it is the most accurate. I don't think I could fit the angle finder on it without pulling the drive shaft IIRC. A phone may fit though.