Check my pinion angle

[mobile chernobyl]

Played around with my adjustable control arms this week and got the pinion angle pretty close to what I believe is the accepted 'tolerance' front and rear. I don't have a manual otherwise I would probably know what this tolerance actually is but from my research it goes something like this:


FRONT PINION ANGLE (Stock front drive shaft)
The general consensus seems to allow the front pinion to be parallel to the front drive shaft with a tolerance of 0 to positive 1 degree in terms of the front pinion pointing ABOVE the front drive shaft because the action/reaction of wheel torque will push the pinion back down into the 0 degree (parallel) realm.

REAR PINION ANGLE (Stock rear drive shaft without SYE or CV drive shaft)
The general consensus seems to allow the rear pinion to be parallel to the harmonic balancer ring with a tolerance of 0 to negative 1 degree in terms of the rear pinion pointing UNDER the harmonic balancer due to the same action/reaction from wheel torque pushing the rear pinion back up into the 0 degree (parallel) realm.

And without further ado... My numbers taken to a 1/4 degree resolution:

And a visual on the rear drive shaft with the vehicle resting on level ground and suspension settled into static sag point:

I'm mainly wondering if the rear drive shaft angles are okay - I've heard so many different numbers I'd just like someone with a stock driveshaft and/or experience adjusting them to weigh in. I've cycled the rear suspension to full droop and I have no bind - I have about 1/8" clearance between the yokes and the valleys of the shaft yokes - so tight... but not binding by any means. Full bump stop on either side poses no issues whatsoever in terms of binding or added friction that I can perceive with my handometer.

Thanks!

 

[Jerry Bransford]

I don't know where you got your general consensus on the front pinion angle but not likely from this forum. The first thing to know is that the front axle's pinion angle takes precedence over the caster angle, and both are affected by adjusting the other. The way to set the front axle's pinion angle is to use the adjustable length control arms to increase the caster angle as much as is possible without causing driveshaft (u-joint) vibrations from an excessive pinion angle. I.E. raise the caster angle until drivetrain vibrations are noticed and then back off just enough until the vibrations from the excessive pinion angle are eliminated.

For the rear pinion angle, since you have the factory single-cardan driveshaft, the pinion angle needs to be parallel to the tcase output shaft angle. That's the requirement set by the factory driveshaft. With the 3" to 4" maximum lift height limitation created by the OE factory driveshaft u-joints, adjusting the rear axle's pinion angle with adjustable length control arms is seldom advised. Most make do with installing a set of 1" taller motor mounts with rubber bushings and/or a t-case drop. A t-case drop by itself not always being enough for a 3" lift but sometimes it is. Often it is required that both a tcase drop and MML be installed.

Also, the pinion angle moves relatively very little under acceleration with a TJ. Its control arms generally limit that to no more than about one degree. It is with older leaf spring designs where that angle change can be greater than one degree.

This is how your rear axle should be set up:

 

[dbbd1]

So, your rear pinion should go down about another degree or so.

 

[Mr. Bills]

I don't know whether it qualifies as a consensus, but this forum's resident expert/designer of jeep suspensions has said that the front pinion angle can be the same or slightly above the front driveshaft angle but shouldn't be lower.

My front pinion angle was equal to my front driveshaft angle before I converted to manual hubs, which for me was the sweet spot where front driveline vibrations were the least and steering return to center was still adequate. I tried raising the front pinion angle one degree above the driveshaft angle but lost just enough additional caster to make steering return to center less than I like so I returned to equal angles. Please note that every jeep is set up differently so your results may and likely will vary.

In the rear, with a single cardan driveshaft, angles "A" and "C" should have the same value but it is generally acceptable for the rear pinion to be slightly lower so long as there are no vibrations. Again, experimentation is the key.

 

[bobthetj03]

You'll also want to check for ujoint bind at full droop.

 

[mobile chernobyl]

Thanks all - And thank you @Mr. Bills for the straight forward response - I will double check those angles to make sure they are correct. I spent a few hours trying to get to the exact scenario you mention and perhaps I read my angle indicator wrong when recording the values because I could've sworn my angle was lower on the pinion vs. the harmonic balancer haha.

No bind at full droop yet. I can see a CV and SYE in my future though with all this angle matching hoopla... was really hoping to not have to buy twice because I want to look for a NV241OR first. T-Case drop is something I'm trying to avoid but if 1/2" does it... I do plan to eventually to a TT mod so I'll need a SYE/CV either way.

 

[k-huevo]

An important factor is missing, and that is the u joint operation angle. Subtract 7.25 from 23.5 = 16.25, which will reduce the service life of the universal joint considerably.


I'm surprised there's no comment about vibration when accelerating.