Caster angle question - JeepForum.com

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post #1 of 31 Old 11-23-2015, 08:42 PM Thread Starter
manvstaco
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Caster angle question

Hello all! I have a question regarding my caster angle and drive-ability. PO installed a 4 inch rough country lift without modifying the caster angle on either axle, it does have the tcase drop but no leafspring/caster shims, steering wheel is a crooked as well (to the left). My friend is telling me to get 3 degrees shims, and I am seeing some of the 4 inch lifts actually come with 4 degree shims. Everything I am reading says to avoid the aluminum ones as the wear out and flatten creating problems. My steering is a bit crazy and am told this would help as it is currently my DD. What do you guys think?
Image below is my caster angle from my alignment a couple weeks ago.

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post #2 of 31 Old 11-23-2015, 08:59 PM
jbolty
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Do you have extra long shackles.
Are your track bars still on?

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post #3 of 31 Old 11-23-2015, 11:27 PM Thread Starter
manvstaco
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Quote:
Originally Posted by jbolty View Post
Do you have extra long shackles.
Are your track bars still on?
PO removed rear track bar and sway bar. I removed the front track bar and reinstalled the sway bar with quick disconnects. I feel like it drives better with track bars removed, and sway bar installed down the freeway. Here are pictures of the front shackles. what do you think? They are beefy compared to some of the goofy stuff I have seen people make. Would changing these out be a better route than caster shims?
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20151123_213440.jpg   20151123_213459.jpg   20151123_213518.jpg  
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post #4 of 31 Old 11-24-2015, 05:02 AM
ACs95YJ
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It looks like you could benefit from a drop pitman arm. You're probably getting a lot of bump steer from the steering angle.


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post #5 of 31 Old 11-24-2015, 05:04 AM
ACs95YJ
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Also, on my rear axle I actually had to run 8 degree shims. I think every setup, lift, and jeep can be just a little different.


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post #6 of 31 Old 11-24-2015, 08:26 AM
Randonexplosion
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Those shackles appear to be 6" bolt to bolt, so they are a 1" lift shackle. That will rotate your axle forward and negatively affect your caster. I felt a big (bad) difference just installing 5/8" lift shackles.
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post #7 of 31 Old 11-24-2015, 10:52 AM Thread Starter
manvstaco
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Quote:
Originally Posted by Randonexplosion View Post
Those shackles appear to be 6" bolt to bolt, so they are a 1" lift shackle. That will rotate your axle forward and negatively affect your caster. I felt a big (bad) difference just installing 5/8" lift shackles.
So what should I do? Caster shims or new shackles?
Also the pitman drop arm, would this work ?
http://www.quadratec.com/products/16197_150.htm
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post #8 of 31 Old 11-24-2015, 11:02 AM
Randonexplosion
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Can you stand to lose an inch of lift? I tried doing some shims up front but I didn't notice any difference. Can't remember which ones I used.
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post #9 of 31 Old 11-24-2015, 11:24 AM
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Quote:
Originally Posted by manvstaco View Post
So what should I do? Caster shims or new shackles?
Also the pitman drop arm, would this work ?
http://www.quadratec.com/products/16197_150.htm
Drop pitman arm won't fix your caster, though it may help bump steer. Going to a 1/2 inch shackle lift may do the trick. Never tried shims up front, but never heard any positive results from it either. They also have adjustable ball joints, but the simple fix would seem to take the shackle lift lower.

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post #10 of 31 Old 11-24-2015, 11:28 AM Thread Starter
manvstaco
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Quote:
Originally Posted by Reno72 View Post
Drop pitman arm won't fix your caster, though it may help bump steer. Going to a 1/2 inch shackle lift may do the trick. Never tried shims up front, but never heard any positive results from it either. They also have adjustable ball joints, but the simple fix would seem to take the shackle lift lower.
I've got tons of bump steer, would that pitman arm drop link I provided above work for me? Anything else I should buy along with it?
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post #11 of 31 Old 11-25-2015, 07:04 AM
JeeperDon
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A stable ride is not determined by the caster angle directly. It is determined by a proper 'Lead Point to the Contact Point' distance (see photo). The OEM caster angle was/is specified for stock size tires. If you increase the diameter of the tire, the Lead to Contact distance increases.

It's fine to have a less than spec caster angle for larger tires. I also question the target number on that readout sheet. When mine was done at Firestone, the target was 6-6.5°, not way up to 9°. Having 5° with 33's would end about the same Lead to Contact distance as 6-6.5° with stock tires. I'll leave it to you to do the trigonometry to see what your Lead to Contact is now. I doubt at all that your issues are due to caster. So, go with what was said above, fix your steering linkage!
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post #12 of 31 Old 11-25-2015, 07:20 AM
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[Digression: What most new people to Jeeps don't realize is that the whole OEM Jeep was designed as a system, a lot of things with the right specs working together to make a nice stable Jeep out of the dealer lot. Whenever you alter one thing under the Jeep, it cascades around to mess up a lot of other things. In this case, the lift was added with no consideration for the steering. Only after you address all the downstream issues from making one mod will the overall stability be there again.]

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post #13 of 31 Old 11-25-2015, 11:13 PM Thread Starter
manvstaco
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Ok so I bought the drop pitman arm and the puller from quadratec today. As far as my caster angle goes, it seems you guys are leaning towards new shackles. Does anyone have any recommendations? Should I just wait till I have the new pitman arm installed or would changing my caster angle with new shackles be worth while?
Thanks for all the help
http://www.quadratec.com/products/16197_150.htm
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post #14 of 31 Old 11-26-2015, 12:35 PM
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I'd say if you are happy with the lift you currently have out of your spring/shackle combo and your u-bolts aren't rusted to the point that changing shims would be a PITA, I'd use the info posted above about calculating caster/lead/trail. Then order some shims to get the caster correct for your size tires.

If you have enough tire clearance to go shorter shackles, that may be easier, but you may still have a need to swap shims even after going to shorter shackles. It's one of those cases where "you make your choice and puts your money down and takes your chances." (That's the old style of an old quote).

I have a lift kit to install sometime this winter and luckily have 3 sets of shims to play with and can always order more if none of them give me the right pinion angle or the right caster up front.
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post #15 of 31 Old 11-26-2015, 07:52 PM
JeeperDon
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Math is your friend. Reducing shackle length on a YJ by 3/4" (0.78" actually) increases the caster by 1°.

'93 YJ, '02 GM 4.3V6, SOA, dual ARB's, 8.8+D30(WarnHubs), 4.88s, 35" BFG KM2s, AX15, NP231+4:1+SYE+2LO, York OBA, Warn M8000.
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