Very Confused About Caster...

[mccula]

OK after reading http://gojeep.willyshotrod.com/HowtoAlignment.htm and following his instructions, I have measured my caster and using a protractor and a level I got 88 degrees. Looking at his chart, 87.5 degrees/2.5 deg. = 6.5 degrees of caster. So that would mean 88 degrees = 7 degrees of caster. (I have a high pinion). My truck is lifted 3.5" in the front (this is why I'm doing an alignment), and I never changed anything from before I lifted it as far as the control arms or the control arm shims.

Is that OK? 7 Degrees? Or should I add/remove some shims to change it? I'm really super confused as to where it should be at and how to get it there. I just don't understand how it could still be at the right amount after lifting it that much... everyone says it should be way off when you lift.

Please help, thanks!

[HOrnbrod]

 

I've always checked my caster using an angle finder on top of a socket that fits over the upper ball joint. It comes out to +/- 1/2 degree of the alignment machine. I set mine at factory +7 degrees using shims behind the LCA. So do your toe and caster tape measure alignment by whatever method you like best, then go to a reputable alignment shop, see how accurate you were and record any differences. Then you can use this data as a standard for future "garage" alignments.

 

That reminds me, I haven't checked alignment for awhile - will check again tomorrow since I just replaced the drag link.

[mvusse]

With the 4 link, keeping stock control arms, caster doesn't change that much. Bigger problem is toe in. With the stock inverted Y steering set up, lift adds toe in. When I lifted my MJ 4.5" I ended up with 2" toe in and horrendous death wobble. At 25-30mph I experienced a DW episode so severe it fried the alternator bearings, knocked the face plate off the radio and rattled my teeth out of my mouth.

 

After I reset the toe to 0 I had no more DW.

 

With a radius arm setup like a lot of Fords, or a popular (because of price) long arm conversion caster changes a lot with lift. If somebody tells you your caster will change a lot when lifting your Jeep, then they don't understand how your suspension works.

 

Trying to find a happy medium between caster angle and front pinion angle with 6.25" front lift I run about 4 degree caster at the moment with aftermarket adjustable control arms.

 

I just glanced at that site about alignment on lifted Jeeps, but don't know how far to trust it as he specifies 13/15" bolt head on the lower control arm main bolts. They're metric 21mm. 13/16" may work, but is not the correct size.

[HOrnbrod]

Just checked. 68-1/8" front and rear for 0 toe, 6.5* caster both sides. Good to go.

[NotMatt]

I've always had it in my head that anywhere between 5 and 7 degrees is acceptable caster... AND, it's not unheard of for dana/spicer axles to be up to a degree different per side from the factory. When I built my radius-arm style long arms, I shot for about 6 degrees at ride height, which is where the number is most important cause it's where you're gonna be at when driving down the road. With a radius arm setup, the caster will change when flexed or compressed/drooped. With a factory 4-link like you have on a stock or regularly lifted rig, it will not change a whole lot (maybe a slight amount) over the travel of the suspension, due to different length control arms... however it shouldn't change much.

 

They do build in the shim adjustment setup for the lower control arms from the factory, so you can get it dialed in perfect on an alignment rack I guess. In my world, 6.5 degrees is more than acceptable and I would not worry about adding shims to the lower CA's. In fact, I run a kingpin high pinion D60 under my wrangler with about 4 degrees of caster (designed that way to point the pinion up further at the t-case) and full hydro steering... and it still drives down the road straight and true with no ill effects.

 

I would leave your caster where it is, and concentrate on making sure the toe-in/toe-out is dead on or maybe toe'd in just a slight bit (think like 1/8 to 1/4"), and you should have a pretty good handling ride when you're done.

[danbyrambler]

:agree: Kind of - - - Set the toe to Factory - - Zero - - - Now there's gotta be/gonna be a little slop in every system; Make 1/16 r less toe-in your max error limit unless some one can come up with a real world way for identical coefficient of friction for the front tires, then you could probably get away with a little more - Another reason for zero toe being so important is the track bar - - Going up 3-3.5 inches will mean a stock TB is gonna put the axle about 3/8" to the Driver side - No biggie with ZT - Camber doesn't apply unless you're dialed in at over 8-9* caster - - That's when bumps/uneven pavement can make the tire want to steer like a motorcycle - - - tire imbalance, bent rims, loose/worn steering box - - - - all the little things are cumulative - - - ZT can tolerate a fair amount, but a little Toe in/out & a little more wear here & there & Death Wobble is gonna happen - - - - - - My 89 MJ's pretty stock - - Wheels/Tires very close to stock - PO did a 3" lift with a spring swap - 3" confirmed by direct compare with my bone stock 87 MJ - UCAs, LCAs, TB & all other suspension stock - - Caster was 10 - - removed two point 9s & one 4mm from each LCA & caster back to indicated 7.5 on my protractor - - - - No DW with 10* until idiots at alignment shop ignored me & set things to their liking - - - Big time DW afterwards for a few until I got things sorted out & back to zero - Used 2 straight edges secured with rubber straps for alignment & ball joint thing for caster - - removed shims by loosening rear LCA bolt, the 2 shim bolts & undoing TB at the knuckle mount - - - Then started truck, put in reverse, backed a few feet, stompa da brakes, shut off, get out & pick up shims. 2nd pic is how I measured the toe - Two panel hangers from Home Depot electrical dept - two identical rubber straps - carton isn't necessary - once both ends are connected there's plenty of tension to hold them to the tires - 1st time I did this the axle was on stands & tires deflated so the panel hangers rested against the rims - inflated tires for a dbl ck & alignment was same.