Rear Pinion Angle

[Eyedaho]

Thanks for this information, @abuck99. Your description and that link were both very helpful with taking some measurements tonight in preparation for installing my MT UCAs which are getting delivered tomorrow. I greatly appreciate you taking the time to document this.

 

[abuck99]

Thanks for this information, @abuck99. Your description and that link were both very helpful with taking some measurements tonight in preparation for installing my MT UCAs which are getting delivered tomorrow. I greatly appreciate you taking the time to document this.

Admittedly my understanding of the working angles back then was overly complicated. I’ve learned a little more since that post almost 5 years ago.

It's only to say I found the simplest measurement to be concerned about is the angle relationship between Transfer Case output flange and the Rear Diff Pinion Flange- (don’t worry about factoring in the driveline slope) Essentially the Rear Pinion should point UP to the TC. The flange angles should be between 1 and no more than 3 degrees difference and they should be parallel to each other in this relationship: //

TC Flange /————— / Rear Pinion Flange. What you don't want is this relationship: /————— \ ​

** When both flanges are pointing down /--\ it narrows working angles and puts more bind on the spiders (u-joints) this causes more wear and vibes.

I find that using the small digital angle finder is the easiest tool for this job. Find the angle of your TC output flange: let’s say you find its -89.5 (.5 degrees angled downward ) /. Then you find your pinion flange angle and its pointing UP +89.5 (.5) degrees / . This is ideal- the total difference is 1 degree. in reality maybe you find your rear pinion is pointing down 88.0 (-2). You'll need to adjust the pinion up a minimum 2.5 degrees to achieve a 1 degree difference. To point the pinion upward toward the TC, adjust the control arm length. FWIW You'll get the greatest amount of diff angle change with least amount of input by adjusting the upper control arms. You would lengthen the Uppers to pivot the pinion up. You can adjust the lowers but you have to shorten them to pull the pinion up and it take much more thread area to achieve the same result.

Finally- If you're rear upper and lower control arm bushings are new and tight- chances are you won't have to worry about making any adjustments- you'll be with in 3 degrees variance on the average 2" lift.

FWIW Adjustable control arms are problem solvers and stand up to some abuse, but they also open the door to increased frequency of bushing maintenance- if you dont have a problem dont bother with them.

 

[Eyedaho]

Admittedly my understanding of the working angles back then was overly complicated. I’ve learned a little more since that post almost 5 years ago.

It's only to say I found the simplest measurement to be concerned about is the angle relationship between Transfer Case output flange and the Rear Diff Pinion Flange- (don’t worry about factoring in the driveline slope) Essentially the Rear Pinion should point UP to the TC. The flange angles should be between 1 and no more than 3 degrees difference and they should be parallel to each other in this relationship: //

TC Flange /————— / Rear Pinion Flange. What you don't want is this relationship: /————— \ ​

** When both flanges are pointing down /--\ it narrows working angles and puts more bind on the spiders (u-joints) this causes more wear and vibes.

I find that using the small digital angle finder is the easiest tool for this job. Find the angle of your TC output flange: let’s say you find its -89.5 (.5 degrees angled downward ) /. Then you find your pinion flange angle and its pointing UP +89.5 (.5) degrees / . This is ideal- the total difference is 1 degree. in reality maybe you find your rear pinion is pointing down 88.0 (-2). You'll need to adjust the pinion up a minimum 2.5 degrees to achieve a 1 degree difference. To point the pinion upward toward the TC, adjust the control arm length. FWIW You'll get the greatest amount of diff angle change with least amount of input by adjusting the upper control arms. You would lengthen the Uppers to pivot the pinion up. You can adjust the lowers but you have to shorten them to pull the pinion up and it take much more thread area to achieve the same result.

Finally- If you're rear upper and lower control arm bushings are new and tight- chances are you won't have to worry about making any adjustments- you'll be with in 3 degrees variance on the average 2" lift.

FWIW Adjustable control arms are problem solvers and stand up to some abuse, but they also open the door to increased frequency of bushing maintenance- if you dont have a problem dont bother with them.

Thanks, that all makes sense. I needed new control arms anyway since mine have 300k+ miles and the bushings were shot. To keep the cost down and still be able to correct the pinion angle, I went with the fixed lowers and adjustable uppers. I did pick up a Klein digital angle finder from HD, and it worked great to check the angles last night. From reading that link in your old post, I was thinking the minimum 1 degree angle is between each flange and the drive shaft, and that ideally both flanges are parallel. It seemed to say that the minimum one degree angle is so the u-joints flex a little bit to rotate the bearings/bushings and move the grease around for proper lubrication. I won't have to adjust much, but shortening the uppers a little bit should get me where I want to be, and for $300 the MT are going to be worth it to tighten up the rear end. I already noticed a big difference with installing the SPC lowers in terms of feeling less loosey goosey while cornering and hitting bumps. Those bushings were pretty shot after 22 years! Anyway, thanks again for taking the time to explain. I think understand well enough to not make things worse, and I'll definitely focus on at least having the flanges tilted towards parallel like you're saying above.

 

[pili]

Question for those in the know...I'm getting ready to replace my rear control arms as the bushings are very much done. I'm at about 22.75" in the rear with a pinion angle variance of about 3.2º (in the better / / orientation). I'm inclined to stick with stock length arms all around for simplicity, but @ 3.2º, am I causing excess wear on the rest of the driveline?

I'm not noticing any major vibrations from the driveline that I can tell, but every bushing I replace seems to help smooth things out incrementally. So I'm certainly not opposed to getting the perfect pinion angle via adjustable upper arms.

Thanks!

 

[abuck99]

Leave it alone- stick with stock length arms and use rubber bushings.