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7.9 degrees of caster after 4.5" lift install ?

dfarmxj

NAXJA Forum User
Location
western WA
I installed my 4.5" fixed arm kit from rough country over the last weekend, and found that I had vibrations coming from the front ds. I installed a 1" tc drop and had no issues with vibrations from the rear. The vehicle has a low pinion front diff , and I am on the fence weather to change to a hp front diff, or get a set of adjustable upper arms and try to correct pinion angle that way.

As I said in the title, the caster is @ +7.9° with the lca adjustments bottomed out. Will I be able to get the pinion angle decent and still have enough caster to drive normally?

Thanks in advance
 
I guess my question is, will a hp front diff get me a much different pinion angle, or should that be my second option after a set of adjustable upper arms?
 
What is your pinion angle now on both ends of the DS?

A high pinion D30 is generally better than a low pinion unit for overall sturdiness and will help your pinion angle by a degree or two. But, to go high pinion will only affect your pinion angle and not have any affect on your caster.
 
What is the best way to measure pinion angles? I looked @ the diff housing and didn't see a spot parallel to the pinion to put an angle finder.

It kind of looks like control arms will be the smartest first step? Who makes the most cost effective adjustable uppers? The vehicle is mostly a pavement pounder (dd for wife and kids) and family camping, hunting, and general woods bumming vehicle.
 
I used those Rough Country drop brackets to correct this issue on mine. Would have ideally gone with long arms but money was tight so @ $180 the drop brackets worked fine.
 
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What is the best way to measure pinion angles? I looked @ the diff housing and didn't see a spot parallel to the pinion to put an angle finder.
It kind of looks like control arms will be the smartest first step?


If you have almost 8 degrees of caster, on a LP D30, a with 4-1/2" lift, your front pinion angle must be off by many degrees. This is most likely what is causing the vibrations.
The front u-joint, at the axle should be straight with no more than 1 degree of angle change. The FSM indicate that the pinion angle has priority over the caster.

As a comparison, my 01 XJ, with a LP D30, at 4"s of lift, had 3 degrees of caster when the pinion was properly set (using adjustable upper and lower CAs).
I measure the pinion angle, on the axle, using one of the two flat spots on the front of the housing. Others use two of the front cover bolts.
See the link below.
http://jeep-xj.info/HowtoAlignment.htm


You need adjustable CAs when you lift an XJ 4-1/2"s, especially with a LP front axle.
 
I just pulled the jeep into the garage to get some better measurements than before (just threw an inclinometer on the upper bj. In the parking lot @ work), and off of the upper bj I'm reading 10.8° and off of a flat spot on the bottom inner c by the ball joint, im seeing 11.2°. If I measure off of two bolt heads on the side of the diff cover, its tipped towards the front of the vehicle 2.8°.

I see no reason that 1° of caster wouldn't = 1° @ the pinion, so in theory, I should be able to dial in 5-7° of pinion angle and still have good road manners.

Is that correct?

I think I will be ordering a h&t Sye(with a stock front ds) when I order the control arms to get rid of the t-case drop.

With the control arms, Sye, and a set of drop brackets for the control arms, will my xj be happy again?
 
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I'm running a set of fixed arms (upper and lower) with 4.75" lift up front with nearly 0 caster after an alignment. I got a new set of those little "adjusters" that fit inside the lower control arm mounts, and when the jeep was aligned they were able to use those to bring my specs within factory tolerances. I'm running fixed arms built to spec, HP d30, and a stock front dvshaft. I don't think you'll be able to get that much out of those little adjusters for the brackets, but they were a cheap part.
 
Caster and lift have been covered before.

The tough thing is that with a D30 is that Caster (and Camber for that matter) are fixed at the factory in relation to the pinion. Factory adjustment of the pinion angle involved adjusting the lower control arms to get the pinion in-line with the driveshaft. This gets everthing inside of Spec on a Stock vehice, but with 4.5" of lift, and above, this results in an unacceptable caster for most drivers.

There are a couple of "Fixes":

Adjust the pinion a couple of degrees down from optimal and deal with it being "wrong".

Install adjustable upper ball joints. You can then adjust both caster and camber. It will not be perfect, but you won't have to sacrifice pinion angle.

Cut off the outter "C"s and weld them back on in the exact relationship you want them in.

What do I do?
Drop the pinion a couple of degrees, and deal with the fact that Caster (and Camber) are inside of spec and good enough for "Government Work" ;)

-Ron
 
I ordered up a pair of adjustable uppers from iron rock today, and also got my Sye on the way from dirtbound. Now I just need to scare up a front ds and find a deal on some drop brackets for the control arms.

I hope this all fixes my issues.

Thanks again for the help
 
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