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Caster question

9

92tahoexj

NAXJA Forum User
Location
Southwest PA
ok, first off i have a 92 limited w/ 4.0 auto and a select trac and a HP D30. I've got around 4.5" of lift with drop brackets. According to gojeep's chart I need around 5.5 degrees of caster. I have stock length upper and lower control arms at the moment and have only noticed minimal vibes around 70-75 mph and the vibes disappear when I let off the accelerator. My question does it matter that I'm using drop brackets? or does that not make a difference in the caster angle?
 
thanks for the info. maybe i should be more specific since the vibes don't bother me. does the 5.5 degee caster angle apply to a 4.5" lift with drop brackets? or just a 4.5" lift without drop brackets? I'm taking my jeep to get an alignment and I want to make sure they get it correct this time.
 
Caster is more or less independent of your suspension components. With proper caster, you'll have good stability in a straight line, as well as return-to-center. These are all functions on the axle itself, not control arms, angles, etc.

Normally, shoot for factory settings. You'll have to let caster suffer if you get driveline vibrations from your front axle piniont.
 
Any lift height. The 5.5 degree's is the angle Jeep has specified for steering "stability".
Not sure how the steering would feel if the angle is > 5.5 degrees but I had trouble with death wobble when castor was set ~4.5 degrees.
 
I think using shims is a tradeoff. Shims will also affect driveline angle. With the angle ball joints I was able to maintain proper driveline angle (no vibes) and close to optimal castor (5 degrees), The angle ball joints are an expensive option though. The steering was dis-assembled to install the new ball joints. I think I paid ~$200 for the job. You could do the install yourself if you have the time.
 
IF you are going to a run-of-the-mill shop or alignment business odds are they will tell you the caster isn't adjustable on the XJ. This is wrong, but don't waste your time trying to argue with them.

If you are going to a 4x4 shop that does alignments you won't have a problem.

In the 90 FSM the "set to" is 6 degrees; caster is considered Ok if at 5~9 degrees.

I run my 90 with 4.5 inches of lift in the front at 7 degrees.
 
92tahoexj said:
thanks for the info. maybe i should be more specific since the vibes don't bother me. does the 5.5 degee caster angle apply to a 4.5" lift with drop brackets? or just a 4.5" lift without drop brackets? I'm taking my jeep to get an alignment and I want to make sure they get it correct this time.
Click to expand...

The 5.5 degrees in the chart is a trade off between caster and driveline angle. The factory spec for caster is about 7 degrees and for drive line angle is 0-2 degrees. As you lift the jeep the drive line angle gets worse so you have to rotate the axle to compensate. This results in you caster decreasing. If you caster get too low the jeep will wander and the steering wheel won't want to return to straight on is own. At the extreme the steering will want to go to one side rather than going back to straight.

So to answer your question the 5.5 degrees in the chart is pretty much for all 4.5" lifts; however, you can push your front axle forward with reduces you drive line angle so you and increase caster. In fact if you have minor vibration you may be able to clear it up with a slight change to your control arm lengths.
 
Off set ball joints move the axle shaft to inner axle off center.If you look you will see what I mean.I have an 88 xj and there is a built in threaded sleeve that moves the lower ball joit slightly to make the caster/camber adjustable-until you install those greaseable outer seals- It destroyed the one I had on there- That is how I knew it was not in line- also how do you think it will effect the inner axle seal? ask me how I know---I adjusted it back to the middle by eyeball and it was dead on!!!! I have axcess to an alignment machine-.It also will move the shaft slightly outward or inward too.Leave it alone seek elsewhere to adjust!!!!!
Just my $.02
 
Man I just had a BRAIN storm!!!-What if you could make a shim that sits between the uni hub bearing and the outer c? Front wheel drive cars use those on the rear-they use a uni-hub bearing.It wont go anywhere thats for sure!!! Hmmmmm........................:read:
mostly only for camber reasons-use the lower-upper arms for caster just to keep the axle shaft inline still
http://www.ingallseng.com/shims/
GM and Crysler use 3 bolt hubs-
here is what the front lower looks like on an 88
http://www.ingallseng.com/ik3137t-ball-joint.html
 
Last edited:
markaboo929 said:
Off set ball joints move the axle shaft to inner axle off center.If you look you will see what I mean.I have an 88 xj and there is a built in threaded sleeve that moves the lower ball joit slightly to make the caster/camber adjustable-until you install those greaseable outer seals- It destroyed the one I had on there- That is how I knew it was not in line- also how do you think it will effect the inner axle seal? ask me how I know---I adjusted it back to the middle by eyeball and it was dead on!!!! I have axcess to an alignment machine-.It also will move the shaft slightly outward or inward too.Leave it alone seek elsewhere to adjust!!!!!
Just my $.02
Click to expand...

Some axles have the inner threaded sleave and some don't. The ones that have the sleeve work better with offset ball joints as you can get a offset sleeve for the lower and use a offset joint for the upper. This allows you to keep the axle centered in the housing. The ones without the sleeve only use a offset joint and have the problems you mention.
 
lpennock said:
The 5.5 degrees in the chart is a trade off between caster and driveline angle. The factory spec for caster is about 7 degrees and for drive line angle is 0-2 degrees. As you lift the jeep the drive line angle gets worse so you have to rotate the axle to compensate. This results in you caster decreasing. If you caster get too low the jeep will wander and the steering wheel won't want to return to straight on is own. At the extreme the steering will want to go to one side rather than going back to straight.



So to answer your question the 5.5 degrees in the chart is pretty much for all 4.5" lifts; however, you can push your front axle forward with reduces you drive line angle so you and increase caster. In fact if you have minor vibration you may be able to clear it up with a slight change to your control arm lengths.
Click to expand...

I'm not sure what my caster or driveline angle are right now. I don't have a flat place to check it or the angle finder. when I installed the drop brackets I re-used the shims that were behind the lower control arms. there were 3 of them, on thick one and two thin ones. I haven't really noticed any vibes, but my jeep does wander. I'm currently using the factory uppers and lowers until I can afford adjustable ones since the chart shows I should have factory length arms. Should i get adjustable upper and lowers or fixed ones? Should I pull out those shims I installed behind the brackets?
I also have a 1" transfer case drop installed as well.
 
92tahoexj said:
I'm not sure what my caster or driveline angle are right now. I don't have a flat place to check it or the angle finder. when I installed the drop brackets I re-used the shims that were behind the lower control arms. there were 3 of them, on thick one and two thin ones. I haven't really noticed any vibes, but my jeep does wander. I'm currently using the factory uppers and lowers until I can afford adjustable ones since the chart shows I should have factory length arms. Should i get adjustable upper and lowers or fixed ones? Should I pull out those shims I installed behind the brackets?
I also have a 1" transfer case drop installed as well.
Click to expand...

if your going to get it aligned, get a printout of the alignment specs. or, just get an angle finder for 10$ at any hardware store and find your castor and pinion angles while setting the toe.

without the alignment numbers, your just guessing at what you need.
 
92tahoexj said:
I'm not sure what my caster or driveline angle are right now. I don't have a flat place to check it or the angle finder. when I installed the drop brackets I re-used the shims that were behind the lower control arms. there were 3 of them, on thick one and two thin ones. I haven't really noticed any vibes, but my jeep does wander. I'm currently using the factory uppers and lowers until I can afford adjustable ones since the chart shows I should have factory length arms. Should i get adjustable upper and lowers or fixed ones? Should I pull out those shims I installed behind the brackets?
I also have a 1" transfer case drop installed as well.
Click to expand...

Drive line angle is pretty easy to measure. You can get a harbor freight magnetic angle finder or you can make one with a string, weight and protractor. Position you drive shaft so the ujoint cap on diff side of the ujoint is pointing down. Measure the angle from horizontal of the end of the cap. Then measure your drive shaft angle from horizontal. The difference between the two numbers is your drive line angle.
 
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