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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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#41 · (Edited)
Snap a pic of the Cv joint at the TC. That would be my only concern. Although You have less to worry about since RK coils are rated for your 4 door. Height shouldn't be too extreme. Adjusting the ends. Hmm, not sure. With my TF joints, they had to be turned 360 or the joint would be crooked. 1 turn for me was about 1* iirc.
 
#43 ·
Did you check with RK to make sure they sent you the right CAs? The ones you have may be for a larger lift. Every adjustable CA I have installed could be shortened by at least 3-4 full turns.

How does the Jeep drive?
 
#44 ·
I think there is only one RK front upper, lower, and rear upper.. Two rear lowers.
The rear uppers are only used with the longer lowers to move the axle back. The shorter rear lowers are the ones in his kit.
I don't know how RK is set up. Some company's arms will adjust to stock length. If not uppers are used for pinion/caster.
 
#45 ·
If I can't shorten the LCAs any, is there any other suggestions besides ordering adjustable UCAs?

Is what I'm setting at now gonna tear things up or be a safety concern?
 
#46 ·
If I can't shorten the LCAs any, is there any other suggestions besides ordering adjustable UCAs? Is what I'm setting at now gonna tear things up or be a safety concern?
Could shorten the arms themselves. Prob not worth the cost if somebody is doing them.

Problem? Just keep a eye on the Cv joint.

Do you have a lift height estimate ?
 
#49 ·
Ewe ... Hopefully she settles some. Def try getting those arms back.

That is exactly how I lost my DS. Running 6* caster and 4.5-4" front/rear height.
I guess if I can't then I may have to look real hard into getting the adjustable UCAs. Looks like that would be another $250...uuggh.
 
#50 ·
Just added the rough country front CA drop brackets to my '11 JK with 4 inch lift and 35s.. All I can say is WOW!! What a difference in ride and handling quality. I fought with ordering new adjustable CAs or the brackets.. I don't do any rock crawling so clearance wasn't a big issue.. Didn't lose much anyway. I am just amazed at how much better it handles. We'll worth the 90 bucks!!
 
#53 ·
Pretty sure. I measured twice before installing. Center of bolt hole to center of bolt hole using the measurement for 4drs give in RKs instructions.
 
#57 ·
Yes. From the RK instructions..... 2.5" Front Lower Control Arm Assembled Length = 23 1/8"

Also, I did a lift height measurement on the front based upon a diagram showing stock measurement taken at the shock tower and also taken at the spring perches. Based upon those measurements, I ended up with 3 3/8" of lift on the front.
 
#58 ·
Yes. From the RK instructions..... 2.5" Front Lower Control Arm Assembled Length = 23 1/8" Also, I did a lift height measurement on the front based upon a diagram showing stock measurement taken at the shock tower and also taken at the spring perches. Based upon those measurements, I ended up with 3 3/8" of lift on the front.
I saw that :happyyes:
Do you have a bumper/winch ?

231/8 Is common if that's what they list.
 
#59 ·
No, I don't have an aftermarket bumper or winch yet. On the list though. ;-)

I haven't had a chance to get back under there and take one of the LCAs loose to see if I can shorten it any yet. From what I remember and can see there isn't any real visible threads showing so if I can shorten them any at all, it will only be maybe a half (180*) turn. The krawler joint looks pretty symmetrical in that the protruding sleeve looks like its the same length on either side, so I don't think getting only a half turn will misalign anything.

I also e-mailed with Jason at Krawl-Offroad.com whom I purchased the lift from. He said that, "RK is saying that a castor of anything less that 6* is normal for this setup. So with you being at 5.9*, we should be good. That is for the 1.5” and the 2.5” lifts." My only concern on that is if they are basing that comment on only 2.5" of lift. Although this comment was after I sent him all of my info including lift height.

I think I am still going to:
1. re-check what numbers I get by doing the angle measurement off of both circles on the housing
2. try to get a measurement off of the pinion flange
3. take one of the LCAs loose and see if I can turn it (shorten) it any.

I figure it can't hurt anything, right? Who knows...things may have settled in some since first putting it on and now driving it around some.

It seems to drive just fine both in town, on the interstate and on a real beat up city road.
 
#60 ·
Yes !! that's the key "actual height" although RK did lower the new front coils by 3/8 or so compared to the first gen.
You won't find anybody running close to 6* with 4" of lift. Like I mentioned in my post. 3/3 or even 2/4 (now this is with a double carden) you do have a little more leeway with the stock DS, but risk CV failure.
6* is where I was at with TF lowers and my shaft went bad.
 
#61 · (Edited)
Rather than increase the caster with brackets what about these longer LCAs. I just had my 2014 JKU aligned and the caster measured 2.1* and 2.6* on 2.25" lift from OME coils and shocks only. Right now it drives o.k. but I would love to improve it if I can add these. They claim this will get the caster back to 5.5 or so with a 2" lift. What is too high for a caster reading?

Also, is it o.k. to add the front LCAs now and later do the back? I assume yes as they are not related but I have also made other mistakes so far.

Synergy Manufacturing 8047 - Synergy Manufacturing Front Lower High Clearance Fixed Length Control Arms for 07-14 Jeep® Wrangler & Wrangler Unlimited JK - Quadratec
 
#62 · (Edited)
Yep those will work, But don't go by listed coil height. What's your actual height ? You caster is pretty low and I would assume 3-4"over stock height.

Edit: ok never mind. Those arms come only in one size. The caster/lift height note is a good reference.
 
#63 ·
Details:

2014 Rubicon X
OME 2619 front coils
OME 2618 back coils
OME Nitro shocks front/back
Warn Zeon 10-S winch, hoop, lights (added weight)
Best I can measure the lift was around 2.25" but I am not sure if the X already had some lift over a stock Rubicon.

So, the Synergy CAs should be o.k. right or should I get the adjustable ones (much more money)?

Next very dumb question. If I replace the LCAs will I need to get the alignment redone?
 
#64 ·
With the fixed lca's caster is set depending on lift height. The degrees are shown per inch lift there in the link.
Toe will change but ever so slightly. If you already had it aligned and toe set, you should be fine without another alignment. It's up to you whether you want adjustable arms or not. For what you are after, the fixed should work out just fine.
 
#66 · (Edited)
#69 ·
^^^Well Ken, did it warm up enough for you to pull your top and doors today?
I have mine off, and almost got blown out of my Wrangler today.:crazy:
81 degrees here, but very windy......:iamhappy:
 
#70 ·
Well Ken, did it warm up enough for you to pull your top and doors? I have mine off, and almost got blown out of my Wrangler today.:crazy: 81 degrees here, but very windy......:iamhappy:
Not that warm yet. 41* but soon to drop again and snow.
Daylight savings time ... 1 extra hour of COLD :(
 
#73 ·
Well this has been a great read but I am still unsure of where to got next to fix my angles. I'm either wandering all over the road or have DS vibes. 2013 JKU 3.5" RC lift
Some questions for ya :)

Are you running control arms ?
How about a double carden shaft ?
Are you trying to balance caster/pinion and can't find that "happy" spot ?
What are your currant specs ?
 
#75 · (Edited)
Dam it.. Wifi kicked out ughhh
Let's try this again :facepalm:

4.6 is stock ... 1.4 is right for pinion angle.

0* at the pinion would put the axle at 6* caster and guarantee vibes. Assuming you mean 0* between pinion/driveshaft ?
The front shaft is not under load. Generally u-joints don't like more then 5* . Some get away with it and some don't.

I don't know what you tried. The cam bolts fix caster but add to pinion angle. I see a lot of guys running a 3/3 split but w/ steering a little light.

Did you run it before the cam bolts and still get vibes ? Possible shaft is un-balanced ?
How about toe spec ?

The JK sucks with only 6* separation. A 3/3 split should work. Doesn't guarantee the greatest handling though. Shouldn't be all over the road.

My thinking. If we ran both uppers and lowers pushing the axle out a bit. The angle of the shaft would be reduced, letting you run more separation.
Perfect analogy.
Stand at the base of a mountain and run a string all the way to the peak (this is your driveshaft)
Now stand a mile back and do the same. The angle of that string is reduced no matter what angle your standing at (caster)
Is 1/2 added to CA length going to help ? Sometimes enough to help balance the angles :thumb:

Good luck
 
#76 ·
Dam it.. Wifi kicked out ughhh
Let's try this again :facepalm:

4.6 is stock ... 1.4 is right for pinion angle.

0* at the pinion would put the axle at 6* caster and guarantee vibes. Assuming you mean 0* between pinion/driveshaft ?
The front shaft is not under load. Generally u-joints don't like more then 5* . Some get away with it and some don't.

I don't know what you tried. The cam bolts fix caster but add to pinion angle. I see a lot of guys running a 3/3 split but w/ steering a little light.

Did you run it before the cam bolts and still get vibes ? Possible shaft is un-balanced ?
How about toe spec ?

The JK sucks with only 6* separation. A 3/3 split should work. Doesn't guarantee the greatest handling though. Shouldn't be all over the road.

My thinking. If we ran both uppers and lowers pushing the axle out a bit. The angle of the shaft would be reduced, letting you run more separation.
Perfect analogy.
Stand at the base of a mountain and run a string all the way to the peak (this is your driveshaft)
Now stand a mile back and do the same. The angle of that string is reduced no matter what angle your standing at (caster)
Is 1/2 added to CA length going to help ? Sometimes enough to help balance the angles :thumb:

Good luck
It all makes sense, I just wish I knew exactly what to do before just throwing more money and parts and time into it. I'm in a crunch as I have to drive 600 miles to Ft Eustis on Saturday.
Before the cam bolts the caster was 3.6 and was wandering like crazy. So I used them and now have vibes, it either wanders or has vibes.
I'm considering the CA drop brackets, but dont know if that would help or not.
 
#78 ·
You can remove the shaft a drive without it.
Good way to diagnose vibes too.

What shaft do you have ?

That's what sucks with cam bolts. To remove them you need to weld build the mount holes.

IMO Toe can cause a wandering feeling too.
Rough country shaft, dont know what company they use.
I removed the shaft and drove, vibes were gone.
Toe was good today at the alignment shop.
 
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