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Jeep Jk, Caster and lifting.

405K views 2K replies 190 participants last post by  Rob50lx 
#1 · (Edited)
What is caster, how lifting has a effect on caster, How to read caster, and fixes.

**Caster is the tilting of the uppermost point of the steering axis either forward or backward (when viewed from the side of the vehicle). A backward tilt is positive (+) and a forward tilt is negative (-). Caster influences directional control of the steering but does not affect the tire wear and without adjustable control arms, is not adjustable on this vehicle. With too little positive caster, steering may be touchy at high speed and wheel return-to-center may be diminished when coming out of a turn**



The caster and pinion angles are set. Raising/lowering caster has the opposite affect on pinion, and vise versa.
Problem for some of us, the Jk only has 6* between these two angles. 4.2* caster and 1.8* pinion angle. At stock height the driveshaft is at a decent angle.
What happens when the Jk is lifted ? The higher the Jk is raised from stock height, the axle is rotated up , which actually betters your pinion/DS angle. Caster angle is decreased which might affect handling,
There's a few variables like height, size tire, type of driving, etc. A small drop in caster might not even bother you. If your jeep does not include (at min) front lower control arms or drop brackets. Plan on them if the jeep handles poorly.

If your kit does come with adjustable/fixed control arms. Obviously you will be able to tune to your liking. Most company's shoot for stock 4-4.5* but I've seen people (this includes me) try and run 6* with a modest lift. Your driveshaft won't like this trust me :nonono:

The issue with 4" of lift, there's not enough separation (6*) built into the axle to run a safe balance. Stock caster still might be too much for the driveshaft angle. Running a aftermarket double carden DS, it becomes more of hassle trying to balance the two angles to prevent vibes or TC failure. I've seen 3*/3* of in some cases 2* caster and 4* pinion. I could only imagine how the jeep drives :eek:

Some kits will supply cam bolts. Me personally, I don't care for them. The factory lower axle mount is opened up for a offset bolt which will give a small caster bump.


Then there's control arm drop brackets offered by Rancho, AEV, Rough Country, TNT customs. These provide a very nice ride, not only correcting caster but changing the geometry. These may not be for you on a trail rig where clearance is a concern.

How do you read your caster angle?
Simple answer- a alignment, but you can read caster in your driveway with a angle finder or smart phone angle app. Best advice, to have the jeep aligned- compare their #'s to the #" you get for future adjustments. Ex.. You wanted and set for 4* and the alignment reads 5*. Next time around set your caster to 3* knowing the 1* difference,
I set my lower CA's at the time for 4* and alignment read 4.5* (slaps myself on the back)
There's a couple ways to read caster around the interwebs that really is not accurate. Measuring of the lower C which is a cast surface. Another method is off the upper ball joint, I tried this with no luck.

The easiest and preferred method to read caster off the pinion flange. Ok... That doesn't make sense?? Actually it does. We know the JK has 6* between the two angles. Knowing what your pinion angle -- some simple math --will give you caster.
Here's a pic measuring off the pinion flange



Also the two flat circles on each side of the pumpkin can read pinion also. These 2 spots are perpendicular to the pinion flange (above)



Now take your measurement and total 6
Stock is going to read around +2* or (88*) caster = 4*
If the pinion reads +1* or (89*) caster = 5*
If the pinion reads. 0 caster = 6*


You might have read about people cutting and rotating the factory C's. A lot of fab and welding involved but a option to increase caster on the factory housing,

Aftermarket housings like The Prorock, Taraflexand I believe Curries front housings all have increased caster. Prorock unlimited being around 10*

Rockslide engineering now has a TC brace available. The brace was designed to keep the case in one piece if a driveshaft were to fail. Reasons: out of balance, worn centering ball, too much caster angle (front), not enough pinion angle rear), worn u-joint, etc



I'm leaving this open for any questions or opinions. Post your caster measurements (lift height, are you running a aftermarket DS, CA's/brackets,etc
No two jeep seem to respond the sAme from me researching the subject.y
 
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#280 ·
Hey guys. What is the benefit of the fixed arms over the adjustable? I'm on the road for awhile, but when i get back home, I want to measure and and formulate a plan for my caster issue (if any).
 
#281 ·
cost and no joints to worry about
 
#285 ·
alt 0176 ° works on standard keyboard cool.
 
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#287 ·
jeepers can never stay on track lol.
 
#291 ·
Thanks for your advice Jkeeper. I adjusted the caster and found that somehow The Left UCA was adjusted one full turn more than the Right UCA. I evened them up and than added 1 1/2 turns to improve the caster. I think the slight vibration is pretty much gone and I think maybe that setting them both even improved my Toe-in, is that possible? I will work on the Toe-in some more the next chance I have. I thought the steering was good but this made it even better :) Thanks again.
 
#293 ·
it is 5.xx on both sides. I suppose it didn't have much impact. It did steer very good before. The changes I have made resulted in a very subtle difference. I do believe it is better but it is hard to tell.
 
#295 ·
I have about 12 hours at home today. Here's a picture and the angle measurements. I'm not sure how the math works exactly, so these are the measurements taken with the angle finder on my iPhone. I measured on my driveway, and then turned the jeep 180º in the same spot and measured again. The numbers are pretty consistent.

From the flats on the front of the differential: 3.1º
From the pinion with a socket to the ujoint: 1.9º

Finally, is this the picture you wanted?
 

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#296 ·
I have about 12 hours at home today. Here's a picture and the angle measurements. I'm not sure how the math works exactly, so these are the measurements taken with the angle finder on my iPhone. I measured on my driveway, and then turned the jeep 180º in the same spot and measured again. The numbers are pretty consistent. From the flats on the front of the differential: 3.1º From the pinion with a socket to the ujoint: 1.9º Finally, is this the picture you wanted?
The pinion output is a better spot to measure if the you can hold the socket straight.
Another way to do it ... drop the shaft and measure straight off the flange.

Your caster angle is 2° (if read right). Pinion should be reading close to 4°
Are you on flat ground ?

For kicks ... Read off the top of the ball joints for a direct caster #
 
#298 ·
I have a 15 jkur with a 2.5" MC arb kit with adj upper arms only. The actual lift on my light build is closer to 3.5".
Align specs were
5.1 and 5.3 on caster
.16 total toe and steer straight 0
I'm not getting and vibes but wonder if I should turn the uppers out a touch more to be more gentle on the driveshaft???
 
#299 ·
I have a 15 jkur with a 2.5" MC arb kit with adj upper arms only. The actual lift on my light build is closer to 3.5". Align specs were 5.1 and 5.3 on caster .16 total toe and steer straight 0 I'm not getting and vibes but wonder if I should turn the uppers out a touch more to be more gentle on the driveshaft???
That is a bit high. Your stock shaft won't vibe ..instead the CV will fail with too much caster angle.
 
#306 ·
Alright, just installed a couple "Angle Finder" apps on my iPhone. Measurements done in my garage. Floor measured .8* to .9* so we will call it 1* slope. Measurements at the pinion flange read 1.6* to 1.7*. So 1* + 1.7* = 2.7* caster.... OK, I know I am measuring angles with an iPhone but that seams pretty low considering I only added 1.5" lift as measured at the spring perch as instructed in previous posts. Or am I missing something?

Edit: Ooops I think I forgot this step 2.7* - 6* = 3.3* Caster.... That sounds better. Actually likely closer to 3.5* Caster
 
#307 ·
Alright, just installed a couple "Angle Finder" apps on my iPhone. Measurements done in my garage. Floor measured .8* to .9* so we will call it 1* slope. Measurements at the pinion flange read 1.6* to 1.7*. So 1* + 1.7* = 2.7* caster.... OK, I know I am measuring angles with an iPhone but that seams pretty low considering I only added 1.5" lift as measured at the spring perch as instructed in previous posts. Or am I missing something? Edit: Ooops I think I forgot this step 2.7* - 6* = 3.3* Caster.... That sounds better.
Yep .. Edit looks right.

3.3 is not Terribly low, but there's Room for correction.
 
#309 ·
I originally installed a Teraflex 2.5" lift but found quite a bit of spring sag after installing a Warn full width winch bumper and winch, so I swapped to OME heavyweight springs and ended up with about 3" of lift. Driving I noticed that a could notice more pronouced brake dive, I seemed to feel every pavement irregularity, and the steering felt a bit off. I talked to the Rancho guys at Off-Road expo and after ordered a pair of their geometry correction brackets. Night and day difference. If you are looking for the easy way to correct caster, these are a one hour install. I was originally looking at the AEV brackets (same as the Rubicon Express, BTW) and the Rough Country but these multi-piece set ups just didnt look as robust as the all welded Rancho brackets. So far I'm happy. When the bushings in my front LCAs are shot I might look into replacing them and removing the Rancho brackets but for now they are getting the job done quite well.
 
#311 ·
keeper im not sure about what you mean by front ds boot. should there be a boot where the shaft attaches to tranny? on mine there is not. not since I bought it in 07. it is a 4 door jk by the way. I installed a superlift 4in lift 3-4 years ago, running 35s. and yes, I installed the dreaded caster bolts. its been ok. until today. today I installed the aev dropdown brackets and man what a difference. handles like a dream. I have the tf cam eliminator washer kit but cant decide if I want to change it now. looking at pinion angle by eye it looks good but I still might swing by the shop Monday afternoon just to get an exact number. but if I do can I switch back since I did have to grind out a little for the cam bolts or do I need something else entirely?
 
#312 ·
It's not really a boot .. The CV joint has a rubber cover that holds in the grease. Once that splits grease spits out all around the joint.
The cam bolt eliminators close in the widened hole made for the cam bolts. You would do that if you wanted to install adjustable control arms.
 
#313 ·
I went back out with a flashlight. I see what your talking about.almost like a rubber seal with a clamp around it. I was more concerned the the aev brackets giving me too much caster and killing the ds. ill get it checked tomorrow just so ill know for sure what I got. kinda hard for you to answer not knowing what the caster is now. but I thank you for the very quick r
esponse. ive grown to be 52 yrs old and sometimes impatient. I miss the simplicity of my old cjs.thank you again for your response.
 
#314 ·
I went back out with a flashlight. I see what your talking about.almost like a rubber seal with a clamp around it. I was more concerned the the aev brackets giving me too much caster and killing the ds. ill get it checked tomorrow just so ill know for sure what I got. kinda hard for you to answer not knowing what the caster is now. but I thank you for the very quick r esponse. ive grown to be 52 yrs old and sometimes impatient. I miss the simplicity of my old cjs.thank you again for your response.
The 2 circles on each side of the front diff.
Place a angle right there. You want around 2°
If it reads 0 you have too much caster angle.
 
#317 ·
not sure why I am getting confused but for some reason I am, head must be still buzzing from the incredible finish of the Super Bowl.

So what would be better for the drive shaft casters of 3.7/3.5 no geo correction bracket or with geo correction bracket 4.5/4.8? thanks
 
#318 ·
not sure why I am getting confused but for some reason I am, head must be still buzzing from the incredible finish of the Super Bowl. So what would be better for the drive shaft casters of 3.7/3.5 no geo correction bracket or with geo correction bracket 4.5/4.8? thanks
What a game .. Pats got a gift.

Lower caster = better pinion angle. No geo brackets.
 
#321 ·
mine has 2-2.25" lift according to the common diagram that is floating around here. So here is another question would the caster on the driver's side be the one used to determine pinion angle? Because if that were the case I would have 1.5 now with the aev geo brackets in place and 2.3 without them. My wife swears my jeep rides better with the geo brackets I can not really tell a difference. I just now the angle where the front d/s goes into the tc looks steep to me (with geo brackets) maybe it is ok. My front shocks are not over long I measured them at ~24" fully extended even tho Rancho says they are 23.58".

 
#323 ·
mine has 2-2.25" lift according to the common diagram that is floating around here. So here is another question would the caster on the driver's side be the one used to determine pinion angle? Because if that were the case I would have 1.5 now with the aev geo brackets in place and 2.3 without them. My wife swears my jeep rides better with the geo brackets I can not really tell a difference. I just now the angle where the front d/s goes into the tc looks steep to me (with geo brackets) maybe it is ok. My front shocks are not over long I measured them at ~24" fully extended even tho Rancho says they are 23.58".
Pinion/caster are inversely related. The separation between the 2 angles is fixed (on a JK) @ 6°. That's where we get the 4° caster/2° pinion stock. Understand caster ranges from one jeep to another. Jeep A might read 3.5° caster (or 2.5° pinion) and jeep B might read 4.5° caster (or 1.5° pinion) or any thing in-between.

Lift height rotates the differential (pinion) up "positive" Adding pinion but subtracting from caster.

example (stock) your JK measures 4/2. Adding 2" of lift, it now measures 3/3
The AEV 2.5 holes are positioned inward. So you would not get the caster bump if using the 3.5 or 4.5 holes.

The differential side looks angled up a bit (good)
The TC side is what it is. Lift height determines the angle at the TC. When that joint goes .. Your better off with a double carden driveshaft that can take on more of a angle (at the TC) "BUT" pinion/caster become a balancing act which can be frustrating to some.
 
#322 · (Edited)
Drive line angles should be the priority over Caster, when a choice has to be made. But keeping in mind, that caster is still very important for proper steering and handling.!!!IMO

When running parallel Drive line working angles, the rule of thumb is, that the squares of the working angles shall never vary more than 4 degree's difference.

Example 1: You have a 1 degree WA on one end, and a 2 degree on the other end. 1 degree square = 1 and 2 degree's square = 4. So the difference in 3 degree's sq. This is the optimum setting, and you will not have a Drive line vibration with this setting.

Example 2: You have a 2 degree WA on one end, and a 3 degree on the other end. 2 degree's square = 4 and 3 degree's square = 9. So the difference is 5 degrees sq.
This will give you some vibration!

Example 3: You have a 1 degree WA on one end, and a 3 degree on the other end. So 1 degree square = 1 and 3 degree square = 9. So the difference is 8 degrees sq.
This will give you a serious vibration, wear out your u-joints, input and out put bearings, and possible twist a Drive shaft.

So this is why it is very important to keep your Working Angles to the minimum!

Also when running a needle bearing u-joint, you don't ever want the angle to be 0 degrees, because the needle bearing will wear into the cross. The needle bearings must rotate for the u-joint to live!!!!!!

The above is the guideline that Rockwell International uses, when diagnosing
Drive line vibrations, and then adjusting for the solution!

Part of my work tenure was with Rockwell International!

So I hope that the above helps........:thumb:
 
#324 ·
Drive line angles should be the priority over Caster, when a choice has to be made. But keeping in mind, that caster is still very important for proper steering and handling.!!!IMO When running parallel Drive line working angles, the rule of thumb is, that the squares of the working angles shall never vary more than 4 degree's difference. Example 1: You have a 1 degree WA on one end, and a 2 degree on the other end. 1 degree square = 1 and 2 degree's square = 4. So the difference in 3 degree's sq. This is the optimum setting, and you will not have a Drive line vibration with this setting. Example 2: You have a 2 degree WA on one end, and a 3 degree on the other end. 2 degree's square = 4 and 3 degree's square = 9. So the difference is 5 degrees sq. This will give you some vibration! Example 3: You have a 1 degree WA on one end, and a 3 degree on the other end. So 1 degree square = 1 and 3 degree square = 9. So the difference is 8 degrees sq. This will give you a serious vibration, wear out your u-joints, input and out put bearings, and possible twist a Drive shaft. So this is why it is very important to keep your Working Angles to the minimum! Also when running a needle bearing u-joint, you don't ever want the angle to be 0 degrees because the needle bearing will wear into the cross. The needle bearings must rotate for the u-joint to live!!!!!! The above is the guideline that Rockwell International uses, when diagnosing Drive line vibrations, and then adjusting for the solution! Part of my work tenure was with Rockwell International! So I hope that the above helps........:thumb:
Not according to somebody we know :D
 
#325 ·
^^^See there, we just learned something from we know who........:rofl2:
 
#328 ·
Ken, I look at these Forums as a opportunity to learn from other, along with sharing our backgrounds of experience and knowledge. In other words we try to help each other!

Obviously where you asked that question, there is a individual that already has all of the answers, right or wrong. But they are always correct, because he rules in his Kingdom.
Individuals of that type, will always perceive somebody else with some knowledge as a threat. They don't ever want anybody questioning their answers and authority.
It's called the real world!!!!!!!!!!:beerme:
 
#331 ·
well kjeeper the trip to the shop was almost a waste. no printout but I did see my caster as a little over 5 on both sides. he adjusted the cam bolts down to 4.44 and 4.68. doubt they will stay there long. I went to mark them when I got home, one side cam washer is down, other is up. what???
atleast he didn't charge me. think im gonna go ahead and put those cam eliminator washers on now. what do think should be the maximum caster in your opinion? it did drive good but I was thinking 5.3 or 5.4 was too much.
 
#332 ·
well kjeeper the trip to the shop was almost a waste. no printout but I did see my caster as a little over 5 on both sides. he adjusted the cam bolts down to 4.44 and 4.68. doubt they will stay there long. I went to mark them when I got home, one side cam washer is down, other is up. what??? atleast he didn't charge me. think im gonna go ahead and put those cam eliminator washers on now. what do think should be the maximum caster in your opinion? it did drive good but I was thinking 5.3 or 5.4 was too much.
4.5 is perfect. Target that if you get rid of the cam bolts.!
 
#333 ·
ok the cam bolts are gone:) I feel better knowing that the bolts cant shift any now. ill slip back by the shop sometime just to see where its at now. if hes not busy he will hook it up and not charge me anyway. its great to have friends.:beerdrinking:and I thank you sir for nudging me in the right direction.:Thanx:
 
#335 ·
Hello,

I was hoping for someone to answer a question for me.

I have a 2013 2DR Rubicon with JKU 18/60 springs and a Teraflex 2.5" Budget Boost. 35" Trail grapplers with 26-28 PSI. (lower psi helped some)

Steering is flighty on hwy and I daily drive 50 miles. I purchased Rancho drop down brackets last night -- to see if they help after reading the good reviews.

After I install the Rancho brackets, will my drive shaft be even closer to the factory exhaust?

Thanks

Mike - Florida
 
#336 ·
The brackets with greatly help your situation.

There is pinion change but irrelevant to what you're asking.
DS/exhaust contact is a concern Running longer shock or extensions, and disconnecting the sway bar (off road).
Flex the front axle ... If the DS contacts the crossover .. You need the spacers, a smaller ID shaft, AFE y-pipe or custom work.
 
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