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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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#2 ·
So, I had a 2.5" Teraflex lift put on with some 315/70/17 Duratracs. Steering felt a little off so I figured to get an alignment done. After it was done the steering improved but still feels a bit loose. Thinking of adding a stabilizer to see if it helps. This was the report I received on the alignment. Anyone have any input as I am not too mechanically inclined!
 

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#3 ·
Thanks for posting. Look at your final caster spec
Before or final because with the stock housing -caster is not adjustable. From my own experience, a 1* bump In caster will help a lot.
Yours is around 3* about 1-1.5 less then stock.

Do you wheel where clearance is a concern?
A set of drop brackets will really help handling and raise caster.

lower CA's. Adjustable or fixed. These will be longer/adjusted longer then stock,

Or adjustable uppers shorter than stock. These tend to be cheaper but a little harder to install/adjust,

You have a few options. Low caster will def cause some handling issues.
What's your tire psi ?
 
#5 ·
Happy to post and learn :thumb:

Tires are running at 34psi, clearance is not a great concern as of now, the wheeling down here in Va is mostly trails with some small rocks thrown in.

I am always looking to improve the ride as it is my DD, it has the rear drop bracket.

I just hit 6000 miles so many more years to come!!

I am wondering if they could have made the right camber and left toe in spec though??
 
#6 ·
Toe is fine. Camber is not adjustable. If you have a chance. Get each tire off the ground about 3" and pry up from underneath. Ball joints are hard to miss if bad. You can see movement and possibly hear a noise.

I posted a thread on the Rancho drop brackets a few months back. Check em out.

Lastly chalk your tires. That's a 35" right ?
25-28 is typically good for a 35" tire
 
#7 ·
Will do, thanks for the info!

This is why I love WF :thumb:
 
#13 ·
This is a excellent Thread demonstration, of caster, and the effect that it has on your pinion and drive shaft joint working angle.........:awesome:
 
#17 ·
Kjeeper10 I am putting a Prorock 44 ultimate extreme with Reid knuckles with teraflex 4" lift 37 tires. Also synergy tie rod and synergy high steer flipped drag link. Am I missing anything or is there something I should be doing to get the best steering and handling possible.
 
#20 ·
Just be aware. You might be ok with the height, the large loop of the TF track bar can rub the pitman arm. Mine is close but haven't flexed it enough yet.
I think you only have to run Synergy's track bar when running the optional sector shaft brace. The frame bracket by itself is no problem and easily bolted on.

What a setup you're going to have going. You doing RCV's ?
 
#24 · (Edited)
Thanks for the write up! I'm still researching how I want to lift my Jeep and have 1 question. You (and others) have talked about LCA brackets. Using these brackets will change the position of the LCA in relationship to the UCA in that they will no longer be (mostly?) parallel. Does this have any effect on the suspension performance or steering? Also, an adjustable LCA will keep the CA's parallel, but effects (forgot the proper term) instant(?) center? I'm only looking at a 2.5 lift... What issue should I be more concerned about to keep everything working properly? Hope you understand what I'm trying to ask.

John
 
#25 ·
The brackets do a few things, change the operating angle of both upper and lower arms making them more parallel to the ground. This smooths out the ride over bumps.
Change instant center for less brake dive. Lastly the upper arm hole is set back to rotate the axle down for caster. Caster is what tightens the overall steering feel.
Adjustable mid arms only set wheelbase and pinion/caster, But if you are not relocating the mounts -like with a long arm. the geometry doesn't change. Even with adjustable mid arms.
That's where the brackets shine. Clearance is the only negative. Something to consider if rock crawling where clearance needed.
 
#27 ·
Oh, okay... I was under the impression the brackets only changed the location of the lowers. It changes both? Thanks...

John
 
#26 ·
Very informative, wish i would have found it before going through my issues.
Ended up installing just the front adjustable LCA, and ended with 4.8 positive on the drivers side and 4.9 on the passengers side. Sure cured the wandering issue i was having on my '08 JK with a 4" lift and 35's.
Was chasing a steering wobble ( DW if you wish) and also installed an adjustable track arm, with all the correct sized hardware.
Now the 35" Nittos stay on the ground :)

My caster was in the 2.something positive before the LCA's.
 
#30 ·
I put a RockKrawler 2.5 Max Travel System lift onto my '13 JKU this weekend. It's off to the shop for an alignment now. They just called and like many have mentioned on here, the guy brought up cam bolts. Based upon my reading, I told him no on the cam bolts. He said that my castor on one side was just a hair over 5 and on the other was just a hair under 6. I told him I would like a print out and to just get it as close as he can and to not put cam bolts on.

For reference, here are some pics of when I checked it myself after the lift. First pic is of the angle finder sitting on my garage floor to account for any slope in the floor. Second pic is to show where I placed the angle finder. Third pic is the reading of the angle finder.

The front LCAs are turned in (screwed in) just about as far they can go. You might be able to get one full turn out of them...maybe.

What are ya'lls thought on the alignment shop comments and castor as well as how I checked it. I'll post the print out from the shop when I get it.

I drove some and it seem to drive fine although I haven't gotten it on the interstate yet. Only got up to about 50 mph on in town road.
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#112 ·
Can someone "show the work" for his measurements?

When going by what KJ said "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* "

Mag had measurements of +1 on the floor. Then his Pinion was 87. Adjusted for floor slope, he would actually be 86? Is his caster 3?
 
#32 ·
Correct. No upper arms with kit. Still have factory UCAs.
 
#33 ·
Oh ok ... I would be concerned a bit with almost 6* caster if that's what he is getting.

Cam bolts are used for
Increasing caster running the stock arms. To lesson caster (with lower arms) -never heard of that done. Makes no sense
:confused:

As far as the difference from side to side.
The passenger side on JK's always seems to be a bit higher on caster for road crown --I believe. If she drives straight, keep the cross caster and dial each arm back a turn (if possible)

To try and even it out, only dial back the high side. You are shooting for 4.5-5*

At 5.5* average caster.. Pinion angle should show .5 to 0 * or a touch over 90*
 
#35 ·
I think I will try to see if I can get the LCS to turn in (shorter) anymore. Shouldn't affect anything else other than castor right?

Below is a pic of the alignment specs I got back.
 

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#38 ·
I assume that your comment "Pinion angle is changed but in a good way" is in reference to me questioning/confirming that if I try to see if I can get the LCA to turn in (shorter) that it shouldn't affect anything else other than castor. Is this a correct assumption?

Also, do you think that even half a rotation of the joint will make much of a difference? With such a small difference in angles I would think it wouldn't take much.

Also, what do you think of my attempt of checking the angle (see pics in previous post). Based upon the angle finder readings...angle finder sitting on the floor shows 89*. Angle finder on the round ole on the differential housing shows a hair over 87* so let's call it 87.25*. So with 6* separate and taking into account the 1* for the garage floor...that would make caster 4.25*. Make sense?

I know that's a rough way of doing it, but seems like a big difference between my numbers and the shops. Kind of hard to argue though if they've got it hooked up to a computer that that use on vehicles everyday.
 
#39 ·
Yes, the axle measurement is just a base but should get you close setting up arms. Then you would have the jeep aligned for accurate numbers.
That is a big difference though, did you try the other side for s**ts?
There is always a chance the tech screwed up. I don't know how common that is.

What I meant. Lowering caster has the opposite effect on pinion. Your pinion will raise a little which is better for the DS
 
#40 ·
Yes, the axle measurement is just a base but should get you close setting up arms. Then you would have the jeep aligned for accurate numbers.
That is a big difference though, did you try the other side for s**ts?
There is always a chance the tech screwed up. I don't know how common that is.

What I meant. Lowering caster has the opposite effect on pinion. Your pinion will raise a little which is better for the DS
I thought that was a bit of a difference as well. I will try the other side/circle as well just to see. I will also try it at the pinion flange as well just to see what I come up with.

Okay, I thought that was what you meant so I think we are on the same page.

Depending upon what I find by measuring again and in different spots, I will try to see if I can unbolt the LCA and check to see if I can shorten them anymore. Do you think that even half a rotation of the joint will make much of a difference? With such a small difference in angles I would think it wouldn't take much. Also, if my thinking is correct, I should be able to do this with the jeep on the ground....correct? I would disconnect the LCA, shorten it if possible and then use a jack to help rotate the axle to line up the holes by either placing it under the LCA mount or the tie rod close to the joint....correct?

Just FYI...the jeep seems to drive just fine (city and interstate) and I haven't noticed any vibrations or flightiness.

Thanks again. You have been a tremendous help in the process of me installing the lift myself.
 
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