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Front Pinion angle

W

whiskies

NAXJA Forum User
Location
nova scotia
Gents, looked about but cannot seem to find the info I am looking for.
I lifted my XJ 3.5 inches, installed a 231J with a AA SYE installed. I got the rear adjusted right with the pinion aimed at the TC and no vibrations however when I install the front shaft I get terrible vibrations. I did install adjustable LCA however I cannot remember what length they should be? I see some here say adjust LCA so the front pinion angle is 7* to start and fine tune it from there. Where do I measure for the 7*? on the yoke? or top of ball joint
And of course I cannot get the pic to work grrrrrrrrrrrrrrr
 
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Who made the lift kit? Perhaps you can reference their instructions on-line?

The front pinion angle on a Stock XJ is zero (Or 180 depends on how you look at it).
When you lift the XJ using Stock Arms, the Pinion will tend to try and follow that, but your alignment figures may be out of range. As I posted in another thread, most folks go with the pinion a bit lower than the DS. There is no book figure once you leave Stock, too great of an angle and you vibe, too little and it wanders all over the road like a drunk on Heroin ;)

-Ron
 
Sounds like someone was talking about Caster Measurement (7 degrees, OY VEY!).

You want to read/adjust the front DS to Pinion angle. To do this, you use a socket and an angle finder. Find a socket that can sit on the U-Joint cap.
Rotate the front DS so that 2 caps are pointed down. Measure the angle on the Yoke on, the on the DS one. At 3.5" of lift, the difference should not be zero, but a degree or 2 more (Pinion slightly down in comparison to the DS).

So about arm length: Start with stock length (Measure your old arms) and add an inch or so. That will make a nice baseline. Adjust both arms the same exact amount, take a measurement, and do it again as needed.

You are compromising between 2 vehicle characteristics, drivability and u-joint wear/vibrations. Too large of a DS angle and you will get vibrations, straight on and your Caster/Camber may be out of range and it will wander.

And this may seem pretty basic, but make sure your U-Joints are good before you start all this. Nothing worse than chasing vibrations just to find out it was the obvious wear part all along ;)

-Ron
 
Has the original driveshaft ever been rebuilt? My cardan joint was dry after spending 12 years flat. Lifting the Jeep 3.5'' (with LP30) was just too much for the stock, dry, cardan joint.
 
I don't think its the shaft as I have tried 3 different one with the exact same results, I will adjust the arms in a bit this weekend, thanks for the replies guys
 
This is the best way I have found to accurately measure pinion angles front and back. Put your XJ up on jack stands under both axles on level ground making sure to level the vehicle. Make sure to weight for normal driving conditions (1/2 tank gas, you, etc.). You can now put the T-case in neutral and spin both drive shafts from underneath. Use a small digital angle finder to measure the drive shaft angles and the pinion yoke angles. For the yoke angles, you can use a socket that fits inside the hole and sits on the universal joint cap. Make sure to have the yoke straight up and down. Another way is to run a flat straight edge down the machined face of the axle housing at the pinion and subtract from 90 degrees. Either way, you are ultimately looking for pinion angles of 1-2 degrees above the drive shaft angle in the front and 1-2 below drive shaft angle in the back. Theoretically zero is perfect, but the offset allows for axle wrap (twist) under power. This isn't always possible in the front as it will adversely affect the caster angle. That is a bit of compromise and might take some trial and error setting.
 
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Unless the the caster needed puts the drive-line at angles so bad it vibs all day long.

Shoot for good caster but keep in mind the angle of the drive-shaft.
 
souske said:
2° down in the rear for axle wrap.

In the front, you only have axle wrap when in 4wd. So you can cheat the caster a little if needed. Keep in.mind that the front ds is spinning.all the.time, so.dont.get it too.far out of.whack.

This chart may be useful to you: http://www.yuccaman.com/jeep/re_db.html
Click to expand...


If you have axle wrap in the front of a linked rig then you have other problems.
 
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Mach2nh said:
If you have axle wrap in the front of a linked rig then you have other problems.
Click to expand...

I concur, the axle can travel though the travel arc, but wrap will be non-existent on a linked suspension. The reason is basic:
Instead of hanging from a spring, a linked suspension is held at the bottom of the axle, and separately at the top. It simply can't wrap unless the control arms deflect or fail.

-Ron
 
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I think you'd have to use stupidly weak bushings made of Dr Scholes gel to get they type of deflection that needs compensating for.
 
Tom Woods Drive shafts advised those setup numbers to me. I trust they have done their homework. The front angles are more theoretical. It will be pretty hard to get that kind of true front pinion angle and still have decent caster. They recommend that because under load, stock bushings and control arms will deflect up to three degrees. Beefy control arms and heims would allow much less.
 
genevamotorsports said:
Tom Woods Drive shafts advised those setup numbers to me. I trust they have done their homework. The front angles are more theoretical. It will be pretty hard to get that kind of true front pinion angle and still have decent caster. They recommend that because under load, stock bushings and control arms will deflect up to three degrees. Beefy control arms and heims would allow much less.
Click to expand...

I wasn't in that conversation, but it doesn't apply to the XJ/MJ setup with a stock axle.

The factory doesn't even compensate for stock bushings and control arms, and they call for zero degrees.

When you lift the vehicle, the pinion rotates up and your Caster/camber figures slide to the edge of the range. To get them back in range, you need to rotate your axle back towards the way it was, which will result in a pinion below the DS attitude. If you go the other way, the machine becomes un-drivable.
 
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