lift/ castor shim question

[jeremy5780]

I put a 4 inch pro comp suspension lift on my CJ7 and it came with 1 pair of shims, after some research it appears I need the shims on the front axle to adjust the castor back to semi factory specs. My question is what about the rear axle, does this need shims to bring the drive shaft back to alingment?

 

[tarry99]

The front is a given for correcting the Castor...............in the rear you need to measure it and correct if needed.

 

[jeremy5780]

And just to double check ,the fattest part of the shim faces out towards the front bumper?

 

[Posi]

And just to double check ,the fattest part of the shim faces out towards the front bumper?

The thickest part of the shim faces the "rear" bumper on the front axle (positive caster). If you face it towards the front bumper it would lower the pinion (negative caster).

When installing them on the rear axle thickest part faces the front bumper.

 

[mstar]

The thickest part of the shim faces the "rear" bumper on the front axle (positive caster). If you face it towards the front bumper it would lower the pinion (negative caster

Well I'm confused . Anybody else follow this. That seems opposite to what I know about alignment.

 

[Lumpy Grits]

You are returning the caster(increase caster)to spec in the front axle after suspension lift. Thick part of shim goes to the front.
In the rear to rotate the pinion up. Thick part of the shim is to be towards the front.

LG

 

[tarry99]

The thickest part of the shim faces the "rear" bumper on the front axle (positive caster). If you face it towards the front bumper it would lower the pinion (negative caster).

When installing them on the rear axle thickest part faces the front bumper.

Caster and pinion angle are two different measurements and corrections but do interact together.........

The question was how to adjust caster? To adjust caster on the front axle after lift springs have been installed you must normally increase the positive caster which would mean that the top of the spindle has to lean back towards the rear a greater amount..............this would mean that the thickest part of the shim would have to be facing forward to increase "Positive caster".

There may also be some cases where a certain lift spring depending on center bolt placement within the arc of the new spring could be opposite that......

Factory jeeps were set at about 4 degrees positive..........I like to set them up at 5-7 degrees ..............now once you have the caster set you must also address the pinion angle.............and by adding positive caster to help the vehicle steer you have effectively increased pinion angle from the front pinion to the Transfer Case which will make your u-joints at the drive line unhappy.

Solution: a Compromise between the two?.............or removing the spring pads or even removing the outer Big C's at the spindle and re-weld either to the proper settings, since I cannot see what your working on either option may come into play................in either case you can't have it both ways unless you do one measurement independent of the other while trying to correct both.

 

[Posi]

LOL, Yes, what I type was in fact backwards, thick part goes to the front bumper on the front axle. Correct on the rear axle. Sorry for the confusion.
Funny thing I just added front shims on my 69 thick side facing the bumper.

 

[mstar]

after lift springs have been installed [/U]you must normally increase the positive caster which would mean that the top of the spindle has to lean back towards the rear a greater amount..............this would mean that the thickest part of the shim would have to be facing forward to increase "Positive caster".

Yep that's correct.

 

[Lumpy Grits]

IT'S MONDAY ----
LG

 

[Posi]

Must be, can't blame it on coffee.

 

[jeremy5780]

Thanks everyone for there input, now to the next question. My front axle has a steering stabilizer and this has a 1/4 inch steel plate packed in-between the axle and springs on the driver side with a bolt welded to it for the steering stabilizer eye to slide on. is this 1/4 inch difference going to throw off anything? it is only on the driver side. Just curious before I put the shims in.

 

[HackFabrication]

Unless the included shims where made out of steel, I'd put them in the scrap pile. Order a set of steel shims. I got mine from: 6 Degree Axle Shim, 2" Wide | 2 Inch Axle Shims | WFOConcepts.com

I had to use 6* shims on my 2.5" BDS lift to get the caster back to 5*-7*positive. My CJ5 now tracks straight all the way up to 65 mph (I haven't had it above that... Yet...)

I would also recommend that you get it to an alignment shop and see what your caster number is without the shims. No need taking it all apart a second time.

 

[tarry99]

Thanks everyone for there input, now to the next question. My front axle has a steering stabilizer and this has a 1/4 inch steel plate packed in-between the axle and springs on the driver side with a bolt welded to it for the steering stabilizer eye to slide on. is this 1/4 inch difference going to throw off anything? it is only on the driver side. Just curious before I put the shims in.

No issues as long as your U-bolts are long enough for all the extra parts......

FYI , I like to install new U-bolts , they do stretch after use.

 

[Lumpy Grits]

No issue with plate as it was OEM.
X2 on using only STEEL shims and not the cheap zinc castings out there today.
The best place to find steel shims is anyplace that does semi-truck and the like, repair/maintenance.
After you put a couple hundred mile on the Jeep. Re-torque the U-bolts(55ft/lbs). You may want to either cover the exposed thd with a 'jam' nut or grind the thd flush with the nut.
LG

 

[rockinreel]

@Tarry, thanks for that wonderful explanation that castor and pinion angle are not the same thing. I've swapped mine both ways, (4" lift + 1" body) and it definitely drives better with the fat part of the shim towards the front. I don't care about pinion angle. We don't drive in four wheel drive enough to matter. I'll replace U-joints more often for a better ride.

What is the home remedy for measuring castor?

thanks

 

[HackFabrication]

What is the home remedy for measuring castor?

Driving/towing it to the alignment rack and having it checked on their equipment....

 

[Lumpy Grits]

Bad U-joint angles does much more driveline damage than just tear'n up U-joints.
LG

 

[jeremy5780]

Quick question, I bought the steel 6 degree shims. Do you put these shims on the bottom of the spring pack like your adding a leaf, then sandwich them with the plate and u bolts? If I put the shim on the top of the spring pack and sandwich between the axle and leaf spring the center pin that goes into the axle is not long enough once the shim is on.

 

[Lumpy Grits]

Under the axle pad. You put the thick part of the shim towards the outside of the vehicle.
You will need new spring pack center bolts.

LG