Caster vs Pinion angle

I would have asked this question in my other thread but I think it is dormant.
I have freshly installed a lift which was suppose to be 3.5 and ended up at 4. I assume it will settle down a bit.

The caster is off by 4 degrees. I have both upper and lower adjustable control arms that are measured at 15 upper and 16.5 lower.

Two questions.
1. Can I adjust by controlling the torque on the axle from the springs to loosen the uppers? I would do this with a jack under the spring mounts.

2. Which should I adjust, the uppers or the lowers? I am thinking the uppers because they are already at the minimum length and I would need to lengthen them to reduce the caster angle.

If you like your wheelbase then adjust your uppers.

Pinion angle is more important than caster angle. Lots of XJ's have driven lots of miles with less than ideal caster.

The lower control arms set the axle location, the uppers set the caster/pinion angle. Drop one upper control arm from the axle, adjust the length, and use a jack to rotate the axle so you can re-install the bolt.

Ah yes, the compromise between caster or pinion angle. What issue are you trying to fix? If you aren't experiencing a problem then leave it alone.

Caster indication is about 10 degrees. Have driveline rumble.

Previous setting at 6 was smooth but the wheelbase was too long causing interference between the spring (MetalCloak) and the drop bracket for double sheer adjustable track arm (IRD).

Just my two cents. I am in Oz, and its a RHD '95 4.0 aw4, 5" lift, 33" Nito's.
I have upper and lower double adjustable control arms, 4.56 locked diffs, ACOS, etc..
I do all my own work but gave it to a shop to chase a left pull while regearing it from 4.88 to 4.56. Regear (G2) went great but alignment was shit.
I reset all my control arms to the available data on line. This was just a base line. I then set my right control arms half inch longer than the left. This doesn't concern you U.S guys, be it sorted my left pull (our roads are cambered down on the left). Once the left pull was sorted, it was time to sort the vibes and steering.


I had a lot of vibes at the recommended control arm lengths. I adjusted my pinion angle using the upper control arms so that i only had a pinion angle of 2*. Just like the rear with a cardon shaft, you can get away with 2*. An initial drive confirmed all vibes had gone. Felt great to drive. I only go up to 65 mph, and up to there, it was all good. Obviously this pinion angle affects caster. I measured my caster using GoJeeps method and calculated true castor at 2*. Some would believe that this is not enough. My Jeep actually responded well to this angle and felt great to drive. No bump steer, no left pull, no adverse steering. Granted, it was very light, almost like power steering on steroids, but it was positive.


The next day, i fitted a RTC steering damper. This type of damper has a spring and once set up, stiffens the steering, controls jitters and makes the wheel more positive. They are cheap and work great.


So, there are options out there and it is a balance between pinion angle and caster angle. Adjustable control arms make dialing it in easy. RTC dampers smooth it all out.


On a side note.. i am considering 2* upper adjustable ball joints in the future to adjust the caster from 2* to 4*. This will further tighten up the steering while keeping the pinion angle within an acceptable spec.


There are other options such as cutting C's etc.. but these can be quite severe.


I am only offering my setup as and example. This may not suit other XJ's and setups, but for me it has worked.



Cheers,

Sorry, could not figure out how to edit my post. I adjusted my LEFT side control arms half an inch longer than the right. This effectively helps RHD Jeeps combat the left pull we have.

alexbrown64 said:

I measured my caster using GoJeeps method and calculated true castor at 2*. Some would believe that this is not enough.
On a side note.. i am considering 2* upper adjustable ball joints in the future to adjust the caster from 2* to 4*. This will further tighten up the steering while keeping the pinion angle within an acceptable spec.
There are other options such as cutting C's etc.. but these can be quite severe.

Click to expand...

Getting the caster angle within acceptable limits is the most important adjustment, when I regeared to 4.56, the front shaft vibrated badly at 60-MPH (100-KM) and above.
I readjusted the pinion angle to 1 degree, per FSM specs and the vibs went away but left only three degrees of caster. It felt squirrelly at freeway speeds.
A set of Napa HD adjustable lower ball joints brought the caster up to almost 5 degrees, not quite enough to meet Factory specs but good enough to drive decently at speed.
Cutting and rotating the Cs is the best way of solving the issue but an awful lot of work.

When I bought my first XJ, 17 years ago, Go Jeep's site was one of my textbooks.
Marcus is an excellent mechanic and metal worker. His ongoing Jeep Willy restoration/hotrod project is amazing, with the Grand Cherokee running gear.
The project is a great read with dozes of detailed photos of every step. Have some spare time.
http://willyshotrod.com

Tim_MN - Great info! Just what I needed to know.

Alexbrown64 - Thanks for sharing the info. Yours may be way different but the concepts still apply. Thanks for the detail with solutions!

Laxyxj - Thanks for taking the time to present all the info. Very informative and helps bring back the confidence that all does not need to be exact! I too used Go Jeep for a number of years. Great info there too.

OH by the way, I do not have a transmission drop installed. Still stock.

A transfer case drop will tilt the engine, adding additional degrees of angular offset to the front driveshaft/front pinion, and will stress the motor mounts.

At about 3-4 inches of lift one should strongly consider installing a Slip Yoke Eliminator (SYE) to address the lift kit caused increased drive line angles.

Tim_Mn Your comment is why I did not install a tranny drop. I did not want to adversely impact the front DL angle. I have extra motor mounts in a box, if I need them!

I did a much better job of measuring the current caster taking Garage angle into consideration and I am at about 13.5*! Clearly I need to do something. The first install ended up with a 6* caster but I did not measure the driveway angle. That set up did not exhibit any DL vibration. I measured both the bottom of the casting under the pinion as well as the U joint mounting surfaces for the straps. Both were 0*. Consequently, I am sure that the Caster measurement will be a good indicator of being in the ball park If someone who reads this has a different opinion, let me know!

IIRC from years past that 1990 era XJ's were not as susceptible SYE installations. Anything over 4 should seriously consider a SYE. I checked my yoke and it looks fine with the current lift. I believe the yoke length changed in the early 90's with the change in the transfer case spline count. I use to have a front shaft for use in the rear DL, as that was one low cost approach. I don't know if I still have that print out or not.