Caster Question

Cujo · Jun 5, 2004

'94 XJ, 8", 35's, Recently put 2" spacer on top of springs to get to 8", whenever I hit a bump in the road at speed, bad DW, plus poor, wandering steering all around. Adjusted out my LCA's about 1/4", DW gone, much better steering. My question is, right now my pinion is at 0* (the front of my diff is exactly perpindicular to the ground, I know that there is a relationship of caster to pinion angle, but I can't remember the exact number), anyway, is that too much of an angle between the front diff and the front drive shaft, or should the diff point more towards the t-case, creating a strighter line?

FernXJ · Jun 5, 2004

You want to have your pinion facing the transfer case. And at your height I don't see you having any Caster with your pinion at the proper angle. If your pinion is a little lower than your needed height and your not getting vibes, you should be ok. Rensing

Gojeep · Jun 6, 2004

I have the information you need on my site but it you say is right it would indicate 9* of caster! I would be supprised you could run it that high at your lift. Most at that height would only get 5* of caster.

http://go.jeep-xj.info

Cujo · Jun 7, 2004

I'm not sure what you mean by "I would be supprised you could run it that high at your lift" When I had the Jeep aligned (at stock height & stock tires), the printout said my caster was 7.5*. If it is 9* now, that would only be a difference of 1.5*, is that really that big of a difference?

Eagle · Jun 7, 2004

Cujo said:
I'm not sure what you mean by "I would be supprised you could run it that high at your lift" When I had the Jeep aligned (at stock height & stock tires), the printout said my caster was 7.5*. If it is 9* now, that would only be a difference of 1.5*, is that really that big of a difference?

What you had at stock height doesn't apply.

Because the knucles are welded to the axles and the axles are welded into the diff, there is a fixed relationship between caster angle and pinion angle. When you increase caster it lowers the pinion, which increases the u-jount angle at the pinion yoke. However, because the front drive shaft is a double-cardan joint, the u-joint at the pinion end ideally should be at zero (pointed straight at the transfer case) plus or minus about 1 degree.

Raising the front suspension automatically increases the pinion u-joint angle even if you keep the caster at stock specs. However, the geometry is such that if you lift the front without changing anything, the front axle will swing down in an arc relative to the chassis, which decreases caster.

GoJeep's point is that the front alignment specs with a stock axle are a compromise at best, because dialing in enough caster leaves an unacceptably high u0joint angle, whereas setting the u-joint angle where it "should" be leaves you with less than enough caster.

Gojeep · Jun 8, 2004

Eagle said:
What you had at stock height doesn't apply.

Because the knucles are welded to the axles and the axles are welded into the diff, there is a fixed relationship between caster angle and pinion angle. When you increase caster it lowers the pinion, which increases the u-jount angle at the pinion yoke. However, because the front drive shaft is a double-cardan joint, the u-joint at the pinion end ideally should be at zero (pointed straight at the transfer case) plus or minus about 1 degree.

Raising the front suspension automatically increases the pinion u-joint angle even if you keep the caster at stock specs. However, the geometry is such that if you lift the front without changing anything, the front axle will swing down in an arc relative to the chassis, which decreases caster.

GoJeep's point is that the front alignment specs with a stock axle are a compromise at best, because dialing in enough caster leaves an unacceptably high u0joint angle, whereas setting the u-joint angle where it "should" be leaves you with less than enough caster.

Perfectly said by the master

Cujo · Jun 8, 2004

Well then, which is more important, a correct driveshaft to pinion angle, or caster angle? Or a happy medium? (If there is such a thing?)

Tom R. · Jun 8, 2004

Well, between the two it's often said the U-joint angle takes precedence over the caster angle. As for me, I try to dial in as much caster as I can without causing vibes on the front drive shaft, which means I place more importance on proper U-joint angle. I just try to get the best compromise I can afford without causing (too much) harm to the U-joint. As a result my jeep has less than ideal steering, but I'm not willing to trash parts.

Tom

Caster Question

Cujo

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