Caster...Am I doing this right?

[Tremelune]

I found it surprisingly difficult to find info on measuring castor on my '83 CJ7, as most seem to say "put an angle finder on the knuckle" without much in the way of pictures or video...I've found that my knuckle isn't exactly flat, so I tried using the a different spot on the axle. Am I measuring this correctly? As near as I can tell, I'm looking at 3-4°:

 

[Tremelune]

I've read that I want 6-8° of caster to keep this thing going down the road straight, and I could use some help in that department, so I'd like to try and hit that mark...but I have questions.

When installing shims, what do I do about the pin length? If I put a 4° shim in there, the pin will only be into the axle spring pad by a couple mm. Is that okay or should I put a longer pin in?

Another wrinkle is that I plan to go down from 33" tires to 31". Caster angle doesn't change with tire size, but the effects of caster changes with tire size, because trail is what affects steering, and trail is measured at the ground.

So...How do people arrive a 6-8° caster, and why don't they discuss tire size and trail? Is it just that trail is hard to measure and caster is not? I'm hoping to get it right the first time...

 

[Lumpy Grits]

You need to check both sides. Your pic. shows 3*. Have you confirmed the accuracy of the tool?
Average out the readings from both sides and then go for 6-7*
Use steel shims-NOT the pot metal ones.
You will also need to check toe-in. You want a teal of 1/8-3/16".
LG

 

[Torxhead]

I am pretty sure you are measuring it correctly, I measured mine that way. You need to measure the steering axis from vertical. You can get extended head pins for those alignment shims:https://www.morris4x4center.com/tie-bolts-3-8-inch-x-3-inch-length-rear-skyjacker-pair-sj-3803.html.

 

[Lumpy Grits]

OP-Were you on a dead-level surface when you took those readings?
May well want to get a printout from a pro shop to compare with.
LG

 

[cglax6]

OP-Were you on a dead-level surface when you took those readings?

May well want to get a printout from a pro shop to compare with.

LG

I'm pretty sure Firestone still takes readings for free and they give you a printout.

Sent via Google translate using braille through Tapatalk

 

[Kane]

You can place the angle finder on the flat top portion of the steering knuckles where the tie rod ends are bolted to.

 

[HackFabrication]

I would highly recommend that you take the CJ to an alignment shop that can give you a computerized readout of caster (also camber and toe-in). Then go from there. You want to have 5-7 degrees POSITIVE caster. A little more isn't going to hurt if you need to shim. You will need longer center bolts for the springs to add the shims. And as posted: Used steel shims. I got mine from WFO Concepts, but there are other mfg's that have them. Get new U-bolts too while you're at it.

If you need to shim, do the grunt labor, then take it back to the alignment shop to do a final check. Tighten stuff down (again), and go for a cruise.

FWIW: I'm running a 2.5" BDS lift, 3/4" ConFerr shacles (3/8" lift), and TSL/SX 32X11.50-15 tires on 8" wide rims. I had to add 6* shims to my 76 CJ5 to keep it in it's own lane. I had '0' degrees caster on one side and slightly negative caster on the other. The shims did the trick, and I'm rock steady at 60+ mph.

 

[JohnKcj5]

I'm pretty sure Firestone still takes readings for free and they give you a printout.

^^^THIS^^^
If you go a few posts down, you'll see where I postetd about alignment specs and what I did to correct it.

 

[Tremelune]

This is what Firestone gave me:



I'm not entirely sure why the "Before" and "Actual" would be different, since they didn't change anything, but I was told the "Actual" was actual.

I'm about to buy some new wheels and tires, after which I'll have an alignment done. Is it wise to trust your average alignment shop that deals with 90% Camrys with an oldass Jeep with biggass tires?

Looks like it's time for some 4° shims...A bit of trigonometry and measurement is showing I currently have 0.65" of trail, and with 6.4° of castor and 31" tires, I'll have 1.6"...Seems like factory was 1.2-1.7 with 235/75-15 tires, via similar calculations, so these all seem reasonable. I'll gladly trade straight-line stability for heavier steering at the moment.

 

[Tremelune]

Actually, I'll probably go with a 3° shim, because that keeps me in the low end of spec, but allows for the future possibility of reducing my rear shackle length to stock, which will increase caster by 0.5-1° (due to leveling the frame a smidgen...might also pull off an old winch)...which would then still be in spec.

Really, anything will be an improvement. The truck feels sound at 60mph, but you can tell that it was set up for rock crawling without much consideration for road manners.

I appreciate all the help here. These CJs have really become niche classics, and a lot of forums are filled with serious ignorance seeking fashionable tires.

 

[hole]

"I'm about to buy some new wheels and tires, after which I'll have an alignment done. Is it wise to trust your average alignment shop that deals with 90% Camrys with an oldass Jeep with biggass tires?"

I assume Hollywoo is close to Hollywood Ca, if so, I can recommend Bear Wheel and Frame in Covina/Azusa for a good alignment shop.

 

[jp360cj]

I would highly recommend that you take the CJ to an alignment shop that can give you a computerized readout of caster (also camber and toe-in). Then go from there. You want to have 5-7 degrees POSITIVE caster.

This is great advice. The angle finder on the knuckle will give you a ball park idea of where you are, but from my experience is usually only accurate within a couple degrees.

 

[Lumpy Grits]

Actually, I'll probably go with a 3° shim, because that keeps me in the low end of spec, but allows for the future possibility of reducing my rear shackle length to stock, which will increase caster by 0.5-1° (due to leveling the frame a smidgen...might also pull off an old winch)...which would then still be in spec.

Really, anything will be an improvement. The truck feels sound at 60mph, but you can tell that it was set up for rock crawling without much consideration for road manners.

I appreciate all the help here. These CJs have really become niche classics, and a lot of forums are filled with serious ignorance seeking fashionable tires.

You want to go towards the 7* setting.
You'll be grateful on a twisted road that you did.
LG

 

[Tremelune]

I just spoke to a Jeep shop and they told me that there are only two adjustments that can be made on these cars: caster and toe-in. Is that...true? Is thrust angle something I should worry about?

Sounds like they wanted $120 to adjust toe-in for me...

 

[Lumpy Grits]

I just spoke to a Jeep shop and they told me that there are only two adjustments that can be made on these cars: caster and toe-in. Is that...true? Is thrust angle something I should worry about?

Sounds like they wanted $120 to adjust toe-in for me...

Find another shop!
Camber can be done-Just a real BH to do.
You can do 'toe-in', in your driveway.
LG

 

[mriplaybass]

I just spoke to a Jeep shop and they told me that there are only two adjustments that can be made on these cars: caster and toe-in. Is that...true? Is thrust angle something I should worry about?

Sounds like they wanted $120 to adjust toe-in for me...

There is a sleeve between the upper knuckle ball joint stud bore, and the upper ball joint stud. The hole in the sleeve is slightly off center to allow for tipping the upper ball joint in or out.
https://www.jeepfan.com/tech/adjusting-camber/

 

[Tremelune]

I got some 4° steel shims from Warrior because they had a nice flat cutout for the bolt and seemed to be of good quality. Installation was fairly straightforward, but now I have heavy steering (though I think it has more to do with removing a 2" bodylift as opposed to the caster changes). It's hard to tell if straight line stability has improved.

 

[Lumpy Grits]

Did you ck the toe-in?
What tire pressure are you run'n?
I take it you have manual steering and not PS??
What size tires and wheels?
LG