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How to Adjust Front Pinion Angle

M

mbogosia

NAXJA Forum User
Location
Nashville, TN
I have a 2" BB on my 99 XJ. Right now my front pinion angle is 4 degrees. It should be at or as close to 0 as possible right? It looks like I have a little room on my mounting holes of my control arms to slide them forward a bit in the holes. This looks like it would move the axle the right way to get me close to zero. Anyone ever done this before? I know adjustable control arms would be ideal, but since I have a little room I thought it might be worth a try.
 
IIRC you want 4 -6 degrees of positive caster (top of knuckles behind the center line of the tube) 0 degrees of caster will reduce the return to center force and the rig will wander more.
 
Remove the budget boost. Voila!

Unless you want to cut the knuckles off the axle, rotate them, then weld them back on you will always have to compromise between caster angle and drive line angle.

Jared:patriot:
 
Pinion angle and caster angle are tied together on a solid axle.
Caster angle affects steering. It's measured from vertical with the car sitting on level ground.
Pinion angle affects drive shaft U-Joint life and driveline vibration. The pinion angle is COMPARED to the drive shaft angle, and/or transfer case output shaft angle. For the front DS on a Cherokee, the pinion should be even(no angle difference)with the driveshaft.

You only need to adjust the axle if you have a vibration problem. Then it becomes a trade-off. As you push the pinion up, you loose caster. Loose too much caster, and highway handling falls off/other problems start to crop up(tire wear, death wobble, etc)
 
I called the dealership about the parts for doing this just the other day. They told me 4* and 9* shims are available for about $5.50 a piece. These get installed between the LCA adjustment bracket and the frame mount. Most will say that proper pinion angle is more important than caster, just be aware that one will affect the other.

One last word of advice, don't over-torque the studs on the back of the adjustment bracket. The brackets cost about $63 a piece from the stealership. Don't ask me why I know... :doh:
 
Well I thought I had my vibrations fixed and it turns out my front drive shaft has a slight vibration now.

My front pinion angle is actually 7 degrees, and my drive shaft is 1 degree the other way. So I am off quite a bit from being equal.
 
emr1101 said:
you guys describe this wierd, its as simple as this: you adjust caster to adjust your pinion angle, not much more to it than that.
Click to expand...

While it may be true that when using shims or adjustable control arms to make your adjustments you cause both your caster and pinion angle to change, you are really over simplifying it. They are not the same thing at all...

Caster is the relationship between your upper and lower ball joints expressed as an angle in comparison to the road surface.

Pinion angle on the other hand is the relationship between your pinion and your driveshaft without regard to the road surface.

If you were to go through the trouble of cutting and rewelding mounting brackets on your axle, you could easily change one without affecting the other.
 
haha ughh yes but your pinion angle is simply affected by your caster. okay, its like this, you use shims or adjustable LCAs to rotate your axle forward or back, this adjusts pinion angle. anyway, OP - just adjust your caster to the slightest amount to get rid of death wobble, there really is no RIGHT way to do this, as Jeep designed this stuff to work on a stock car, if you lifted your jeep 300", your caster would be such that your axle is rotated forward 90* and pinion angle is straight up ( if your P angle was zero, that is). technicalled you COULD give it zero caster at a 300" lift but your pinion angle would be 90*.
 
Well, what I am looking at is a driveshaft angle of close to 0 degrees. My pinion angle is at 6 degrees. If I rotate the angle finder as if I was moving the axle forward it brings the angle closer to 0. So, I need to push my driveshaft forward about 4mm's and it should get my pinion at a better angle in relation to the drievshaft.

I just called NAPA and they have shims for less than $1 each. I am going to pick up a set of 1.5mm and 3.17mm shims. I am going to try the 3.17mm first.
 
Why do you want the pinion angle to be 0*?


I dont know what it is stock, but seems like adjusting the pinion angle to 0* would throw off your caster angle as well.
 
Starboard M said:
Why do you want the pinion angle to be 0*?


I dont know what it is stock, but seems like adjusting the pinion angle to 0* would throw off your caster angle as well.
Click to expand...
For vibration-free operation, 0* pinion angle is good, but I don't think the entire process has been well thought-out, since the caster is undoubtedly all jacked up now.

:shrug:
Jim www.yuccaman.com
 
You always hear to leave your rear pinion a couple of degrees low to account for axle wrap... Am I correct in thinking that you don't need to account for axle wrap with a coil sprung front suspension as the LCAs and UCAs keep the axle from rotating?
 
Nevermind, I found my answer in the similar threads links below...:read:
 
Alright. I stuck a bunch of shims in there and could only move the pinion about 2 degrees. I went from 7 degrees to 4. LOL Seemed like a PITA for 3 degrees. I haven't driven it yet so I'll let you know how it goes.
 
mbogosia said:
Alright. I stuck a bunch of shims in there and could only move the pinion about 2 degrees. I went from 7 degrees to 4. LOL Seemed like a PITA for 3 degrees. I haven't driven it yet so I'll let you know how it goes.
Click to expand...

Please report back how that test ride felt. 3* caster adjustment is huge. Deal with some pinion angularity, your #1 concern should be steering.
 
RenegadeT said:
Please report back how that test ride felt. 3* caster adjustment is huge. Deal with some pinion angularity, your #1 concern should be steering.
Click to expand...

It was actually 3 degrees pinion angle. I just got back from the test ride and it really doesn't feel any different. Still makes a noise at 70mph, and steering feels about the same.
 
UPDATE: I noticed today that the upper control arm bushing over the differential is literally crumbling apart. It is missing about half of the rubber. Could this be causing a slight vibration at 70mph?
 
mbogosia said:
UPDATE: I noticed today that the upper control arm bushing over the differential is literally crumbling apart. It is missing about half of the rubber. Could this be causing a slight vibration at 70mph?
Click to expand...
Yup. Replace that bushing.

Jim www.yuccaman.com
 
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