Caster adjustment advice?

chudlet

chudlet

TJ Enthusiast
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Joined
Apr 18, 2022
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N Idaho
Hey folks. I was looking to dial in my caster a bit last night because my steering is ok, but "light" doesn't really return to center as I would like and came away with questions vs a done task. Setting pinion angle on the rear was easy because the diff has flat spots on the back to measure the angle. I thought I remembered someone telling me there were the same kind of flat spots under the C's to check caster angle, but I did not find them. Could be I just don't know what I am looking for. What I found was a U shaped area with a depression in the middle. I could bridge the sides with the angle finder or sit it on the base of the U, both gave me about the same angle readings. Pics below.

I know I am supposed to shoot for ~ 6* but Driver side is showing 4.5 and Passenger side is showing 7.8. Thus generating a couple questions for my OCD.
1. Am I measuring in the right spot?
2. If I am measuring correctly, shouldn't these be really close to each other? Would 4* difference between the sides indicate a bent or twisted housing?

Any guidance from folks in the know is greatly appreciated.

Driver side
20240206_170919.jpg


Passenger side
20240206_170844.jpg
 
Personally, I would pause everything you're currently doing, and go find one of these "free alignment check" places near you.
Don't have them perform an alignment, but at minimum get the computer printout of what your current specs are.

From there, it doesn't matter how/where you measure from, and your digital gauge will just be used as a tool to close the gap.

For example, if the computer printout says you have 4* passenger but you want 7*, you know that you just need to add 3 degrees to WHATEVER your digital gauge tells you.
Whether your gauge reads 8* or 5*, you just add however many more degrees of angle to reach your desired numbers, despite what your gauge says. If that makes sense.

THEN you can accurately know whether your driver/passenger difference is an actual issue, or a measurement issue.
 
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Sounds like a plan, thank you gentlemen. Drive line angle was just a hair over 10*. I will check the actual pinion angle tonight.
 
chudlet said:
Sounds like a plan, thank you gentlemen. Drive line angle was just a hair over 10*. I will check the actual pinion angle tonight.
Click to expand...
Check your pinion angle from the rear of the axle. With the angle gauge rotated correctly it will directly show the pinion angle.

Pinion angle, where to measure from.JPG

PinionAngleMeasuring1.jpg
 
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Thank you sir. Rear is set and that is exactly how it happened based on your description in various threads. Front is what I am working to get better measurements on.
 
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chudlet said:
Thank you sir. Rear is set and that is exactly how it happened based on your description in various threads. Front is what I am working to get better measurements on.
Click to expand...

the same spots exist on the front. Measure your front pinion angle using those spots. From there, your caster is separated by ~12° (assuming you have a stock Dana 30 axle).

Caster = 12 - pinion

So if you measure 8° pinion, you have 4° caster. Pinion measures 4°, you have 8° caster.

For anybody that has done a high pinion Dana 30 swap, the difference is 9° instead of 12°.
 
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freedom_in_4low said:
the same spots exist on the front. Measure your front pinion angle using those spots. From there, your caster is separated by ~12° (assuming you have a stock Dana 30 axle).

Caster = 12 - pinion

So if you measure 8° pinion, you have 4° caster. Pinion measures 4°, you have 8° caster.

For anybody that has done a high pinion Dana 30 swap, the difference is 9° instead of 12°.
Click to expand...

oh right on, that really helps my OCD need for numbers.
 
freedom_in_4low said:
the same spots exist on the front. Measure your front pinion angle using those spots. From there, your caster is separated by ~12° (assuming you have a stock Dana 30 axle).

Caster = 12 - pinion

So if you measure 8° pinion, you have 4° caster. Pinion measures 4°, you have 8° caster.

For anybody that has done a high pinion Dana 30 swap, the difference is 9° instead of 12°.
Click to expand...

What's the separation on a Rubi Dana 44?
 
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Thank you all for your advice! I checked the angle on the diff and figured I had about 4* castor. Did 2 full rotations on the lower control arms and added about 2.4* (6.4* ish total). Had some vibration at about 60 mph so backed off by 1/2 turn, took me down to right at 6*. Still have a little vibration at 70 so I'll back it off another 1/4 turn when I get home next weekend and see if there is any vibration left. Return to center is nice now and the steering doesn't feel so "light". More like it just wants to stay in the middle of the lane where it is supposed to be. Thanks again!
 
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jjvw said:
Ignore the caster numbers entirely. The front pinion angle takes priority. Add as much caster as you are able to that doesn't induce driveshaft vibrations. You get what you get.
Click to expand...

Do you recall the normal caster difference driver to passenger which I think is to help counter road crown?
 
Woodrow said:
Do you recall the normal caster difference driver to passenger which I think is to help counter road crown?
Click to expand...

I know it exists. But I have never paid attention to it. @chudlet just confirmed why it doesn't matter, when the pinion not vibrating is what determines the caster. 😉
 
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Woodrow said:
Do you recall the normal caster difference driver to passenger which I think is to help counter road crown?
Click to expand...

Well if you believe the readings on my first post it looks to be roughly 3.3* difference in the knuckles. That is built into the axle and no way to really change it unless you were going to cut and reweld a C. Otherwise your just trying to "twist" the axle housing with the control arms, and I can't see how that does anyone any good. Just adding 2* to the whole axle made a large difference in how the frontend handles going down the road. Road crown isn't consistent road to road much less mile to mile. FWIW, the driver side was within a couple tenths of what the diff formula said it was. Like @jjvw said, it doesn't really matter.
 
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jjvw said:
I know it exists. But I have never paid attention to it. @chudlet just confirmed why it doesn't matter, when the pinion not vibrating is what determines the caster. 😉
Click to expand...

I agree with the outlined approach (get as much caster as possible without inducing driveline vibration) demonstrated by @chudlet ‘s work.

Its academic interest on my part but intended to be helpful. Most anyone who has attempted to check the caster on their TJ has found a difference between sides. I know I’m not the only one who wondered “is my axle housing twisted?” I think the spec for cross caster is 0.5-1 degree less on passenger side but I may be wrong which is why I asked.
chudlet said:
Well if you believe the readings on my first post it looks to be roughly 3.3* difference in the knuckles. That is built into the axle and no way to really change it unless you were going to cut and reweld a C. Otherwise your just trying to "twist" the axle housing with the control arms, and I can't see how that does anyone any good. Just adding 2* to the whole axle made a large difference in how the frontend handles going down the road. Road crown isn't consistent road to road much less mile to mile. FWIW, the driver side was within a couple tenths of what the diff formula said it was. Like @jjvw said, it doesn't really matter.
Click to expand...

Yeah, even though the spec is less, I’ve seen several people report numbers in the 2-3 degree range. Measuring caster at the C is a difficult number to reproduce (for me anyhow).
 
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chudlet said:
Well if you believe the readings on my first post it looks to be roughly 3.3* difference in the knuckles. That is built into the axle and no way to really change it unless you were going to cut and reweld a C. Otherwise your just trying to "twist" the axle housing with the control arms, and I can't see how that does anyone any good. Just adding 2* to the whole axle made a large difference in how the frontend handles going down the road. Road crown isn't consistent road to road much less mile to mile. FWIW, the driver side was within a couple tenths of what the diff formula said it was. Like @jjvw said, it doesn't really matter.
Click to expand...

Your first method of measuring should be ignored by everyone. It is a rough forging, not nearly accurate enough for anything worthwhile. The best spot to measure actual caster from is just inboard of the lower ball joint on the machined surface.
 
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