How to adjust caster?

[Longhorn84]

I set my caster indirectly by setting my pinion angle. I check my pinion angle with a magnetic digital angle finder on the machined flat spot next to the diff cover. The low pinion Dana 30 has approximately 12 degrees between the pinion angle and the caster angle, so if your pinion is pointed 6 degrees up, you'll have 6 degrees of caster. If your pinion is 4 degrees up, you'll have 8 degrees of caster.

Manufacturing tolerances put this probably plus or minus a degree, but it should get close enough that if you don't have any vibes after, and you still like what you have with return-to-center, it's good to go. You can get more accurate if you go to a place like Brakes Plus, who do free alignment checks (they charge you if you have them adjust anything). That gives you a baseline, so you can go home with your angle finder and if you want another degree, just adjust to add a degree to whatever your angle finder says you have. Write down the difference between their measurements and yours so you know the offset if you have to do it again.

Thanks, I do plan to take it to an alignment shop to test. If you watch the timestamp on the video you'll see my angles, again the right to left casters were way different, I drove it with no real issues though so maybe the point is moot.

 

[Jerry Bransford]

Old thread but I'm confused on why caster is different on the front and if that's a concern or not, I realize that it is not adjustable since it's a solid axle but everyone talks about how caster and pinion relate but what caster do you use, is it that average between the two sides? And by the way, when I measured mine I had almost 3-4 degrees different castor from right to left.

The factory left-right caster angle difference is .3 to .4 degrees, not 3-4 degrees. Either your axle tubes or knuckles are severely twisted or you mis-measured. The reason for the factory left-right caster angle is to cause the steering to be slightly biased toward the passenger side so the vehicle won't tend to drift into opposing traffic.

Pinion angle always (!) takes precedence over caster angle. Dial in as much caster angle as possible without causing vibrations from excessive pinion angle and you're at the optimal setting. The bigger the tire, the less caster angle that is needed to give good return to center.

 

[Longhorn84]

The factory left-right caster angle difference is .3 to .4 degrees, not 3-4 degrees. Either your axle tubes or knuckles are severely twisted or you mis-measured. The reason for the factory left-right caster angle is to cause the steering to be slightly biased toward the passenger side so the vehicle won't tend to drift into opposing traffic.

Pinion angle always (!) takes precedence over caster angle. Dial in as much caster angle as possible without causing vibrations from excessive pinion angle and you're at the optimal setting. The bigger the tire, the less caster angle that is needed to give good return to center.

Makes sense. I'll recheck tonight when I get home. They are stock axles so I can't imagine they would be able to twist that much with no other side affects.

 

[iviscus]

Yep if I'm not getting any front driveshaft vibration and I have good return-to-center after completing a turn, I would not mess with the caster angle. It's not a critical angle... there just has to be enough so the steering wheel returns to center and not so much it causes vibrations due to an excessive pinion angle.

I have no vibrations on pinion but my steering wheel not return to center and when i go 60 miles pe hs the jeep is unstable goes right left

 

[Brian.souhan]

So read this thread, but not sure it got to what I was hoping for, which is what is the best procedure for adjusting caster…and in my case, is it a good idea given that I only have upper adjustable control arms? I’ve had the alignment done at Firestone (a long time 20 years ago got the lifetime alignment for only $99…now realize how little they do, but still helpful!), and my caster after lowering from a 4.5-5.5 inch set of springs to a 3.5 inch set of springs is less than 1 degree. Given some other issues, I want to get my caster set right…I called 4WP, and the guy didn’t seem confident they could do a full alignment with only upper adjustable control arms…but seems like I can get toe and caster set, and right now camber is good, so if done right think it would be ok…

But if I could do on my own by taking measurements and lengthing the upper arms, I would like to…just not sure how to get the axle to tilt back and forth when the uppers are off…is it hard, are their tricks?

Any thoughts?

 

[iviscus]

Yep if I'm not getting any front driveshaft vibration and I have good return-to-center after completing a turn, I would not mess with the caster angle. It's not a critical angle... there just has to be enough so the steering wheel returns to center and not so much it causes vibrations due to an excessive pinion angle.

My steering wheel not come back when i make a turn. And a dont have death boble what i do have is a dead spot when im going straight should I check de caster?

 

[Brian.souhan]

Also a nite from my earlier, yes never noticed (as probably been this way for years), but I do not have good return to center…

 

[freedom_in_4low]

So read this thread, but not sure it got to what I was hoping for, which is what is the best procedure for adjusting caster…and in my case, is it a good idea given that I only have upper adjustable control arms? I’ve had the alignment done at Firestone (a long time 20 years ago got the lifetime alignment for only $99…now realize how little they do, but still helpful!), and my caster after lowering from a 4.5-5.5 inch set of springs to a 3.5 inch set of springs is less than 1 degree. Given some other issues, I want to get my caster set right…I called 4WP, and the guy didn’t seem confident they could do a full alignment with only upper adjustable control arms…but seems like I can get toe and caster set, and right now camber is good, so if done right think it would be ok…

But if I could do on my own by taking measurements and lengthing the upper arms, I would like to…just not sure how to get the axle to tilt back and forth when the uppers are off…is it hard, are their tricks?

Any thoughts?

Adjustable uppers only would be preferable over adjustable lowers only.

Sounds like yours are only single adjustable though? I would not recommend removing both at the same time because the axle tilt forward and be very difficult to line back up with the rigs weight on it. This is where double adjustable arms absolutely pay for themselves. Hopefully someone will come along with some good advice on doing it with SA arms but I can at least answer your question that yes, you absolutely can adjust your caster with only adjustable uppers.

 

[Brian.souhan]

Yes, was looking, but sadly only single adjustable…yes, I guess that was my biggest question as well, can I remove them with the rig on the ground and then adjust…but it sounds like they will try to rotate forward, which I’m translating as bringing the pinion higher, opposite the way I need to go. I was hoping that it would be stable and I would need to figure out how to rotate the pinion down.

Im not worried about angle calculation as I know what it is from Firestone alignment, so as I’m sitting on the garage floor, I just need a consistent spot to measure angle and rotate 4-5 degrees.