Rear pinion angle measuring locations

[Midtenn]

I have a little vibration around 40-50 mph and working to iron it out on a nice day. I have a stock driveshaft with a 1.5" TC drop and 3.5" lift. I have double-adjustable rear upper control arms so I'm confident I can set the pinion angle correctly, I just want to ensure I'm measuring from the right spot.

In the pictures below, I've looked at measuring from the top of the harmonic balancer and got 8.1*, then from the side and got 8.8*. (a) which one is correct to measure?

I figured the top was more accurate than the side and got the rears as close as I could. I measured them at the circles next to the back of the pumpkin. (I found this to be commonly referenced and feel confident about this. This is what I can adjust...by the TC case doesn't seem to adjust.

I've also included pictures of the entire setup in case I'm totally wrong.


EDIT: Some of the pictures are sorta dark. For whichever is unclear, I'm going to reshoot for clarity.

 

[Midtenn]

I went to a computer, realized pictures where bad and so here’s new ones.

 

[LieutenantJohnson]

I have never used an angle finder to set my pinion angle. I only used one when I went to 1tons, so I could setup close to stock specs.

If you are dealing with vibes, you should be adjusting slightly (up OR down) then taking for a ride to see if vibes increased or decreased. Not all jeeps are the same. The process takes a little longer, but the results are real to YOUR jeep, not some degree posted online that "should" work.

 

[JMT]

You want yours like the bottom diagram. With your lift size and TCase drop, you may want to get a MML to tilt the transfer case downward slightly, something you can't do by adjusting CA's. This will decrease that angle at the TCase yoke.

 

[Midtenn]

You want yours like the bottom diagram. With your lift size and TCase drop, you may want to get a MML to tilt the transfer case downward slightly, something you can't do by adjusting CA's. This will decrease that angle at the TCase yoke.

View attachment 230713

Yes, I was following that picture. I just didn't know exactly where to place my angle finder.

 

[freedom_in_4low]

Yes, I was following that picture. I just didn't know exactly where to place my angle finder.

here for the axle:

here for the t-case output (though I would orient the finder so it's more straight up-down with the ground to make sure it's reading accurately)

Based on the readings it looks like you're already pretty darn close. Maybe the pinion could come up a hair, but less than a degree as you definitely don't want it higher than the t-case output and in fact being a little lower (0.5-1°) can be helpful so that when the pinion pulls up under load, it pulls up into a vibration-free position.

Keep in mind that u-joints have an operating angle beyond which even a perfect pinion angle won't dial out the vibes. Your operating angle at the transfer case is 11.4 (20.1 - 8.7), which is on the sharp side. I dealt with this on my TJ and even with a MML and a perfect pinion angle still had to have a 1" transfer case drop until I finally caved and got an SYE.

I can't remember where I found this, maybe the Spicer website, but this suggests that it may not be possible to dial out vibrations at the angle you're working with and the driveshaft speeds we often run. (35" tires with 4.88 gears runs the DS at 3675rpm @ 75mph)

DS RPM	MAX NORMOP ANG
5000	3.25
4500	3.67
4000	4.25
3500	5
3000	5.83
2500	7
2000	8.67
1500	11.5

 

[Midtenn]

here for the axle:

View attachment 230721


here for the t-case output (though I would orient the finder so it's more straight up-down with the ground to make sure it's reading accurately)

View attachment 230722

Based on the readings it looks like you're already pretty darn close. Maybe the pinion could come up a hair, but less than a degree as you definitely don't want it higher than the t-case output and in fact being a little lower (0.5-1°) can be helpful so that when the pinion pulls up under load, it pulls up into a vibration-free position.

Keep in mind that u-joints have an operating angle beyond which even a perfect pinion angle won't dial out the vibes. Your operating angle at the transfer case is 11.4 (20.1 - 8.7), which is on the sharp side. I dealt with this on my TJ and even with a MML and a perfect pinion angle still had to have a 1" transfer case drop until I finally caved and got an SYE.

I can't remember where I found this, maybe the Spicer website, but this suggests that it may not be possible to dial out vibrations at the angle you're working with and the driveshaft speeds we often run. (35" tires with 4.88 gears runs the DS at 3675rpm @ 75mph)

DS RPM	MAX NORMOP ANG
5000	3.25
4500	3.67
4000	4.25
3500	5
3000	5.83
2500	7
2000	8.67
1500	11.5

Thanks so much...that is exactly what I'm looking for. And you are right...I'm trying to smooth this out with a big bag of tricks when it sounds like I just need to give up and go with the SSYE.

 

[freedom_in_4low]

Thanks so much...that is exactly what I'm looking for. And you are right...I'm trying to smooth this out with a big bag of tricks when it sounds like I just need to give up and go with the SSYE.

Yeah, I used washers to figure out the least TC drop I could get away with. It was sooo time consuming...add a washer, set the pinion angle, test drive, repeat. I got it figured out and then a year later regeared. The difference in DS speed from 3.73 to 4.56 brought the vibes back and I was gonna have to do it all over again. That's when I finally just bit the bullet. I was so irritated with it by that point that I just threw the kitchen sink at it and spent an extra ~$250 so I could get the super short and avoid ever dealing with it again.

 

[LieutenantJohnson]

Add some washers at the tcase skid for now IF you can't dial in the pinion angle and get rid of the vibes. SYE will be in your future...

 

[Matt131]

L

Add some washers at the tcase skid for now IF you can't dial in the pinion angle and get rid of the vibes. SYE will be in your future...

location for your measurements are good. Looks like you pinion needs to come up a little.

 

[Jerry Bransford]

The two flat machined surfaces at the rear of the pumpkin on the sides of the diff cover are exactly 90 degrees from the pinion angle. Hold the angle finder as shown below and that will directly indicate your pinion angle.

And if you'll get an angle finder like shown below you'll find it to be an easier way to measure and compare angles. Digital is sometimes good, analog is too... and for most things on the Jeep I prefer analog gauges and analog volt-ohm meters.

 

[Cross-Threaded-06TJ]

Add some washers at the tcase skid for now IF you can't dial in the pinion angle and get rid of the vibes. SYE will be in your future...

^^^This is your only solution for now, minus SYE, CV and upper rear adjustable arms.

Your pinion is 7.9 up. Your T-case is 10.1 down. You are within 3 degrees of each other, but you operating on a 20 degree slope, which means your U-joint at the diff is at 12 degree operating angle which is pretty high.

I have read 15 degree is max angle and that is for lower speed. Most OEM I remember won't run higher than 7 degrees of operating angle. And they really want 3.


If you lowered your t-case just a pinch more it will calm down some.

 

[Cross-Threaded-06TJ]

It looks like you have adjustable upper rear arms in the first pic?

So as stated before rotate your pinion up a few degrees, and that may resolve it also for now. until you buy that SYE.....

 

[Midtenn]

I already have a 1.5” tc drop. Are

^^^This is your only solution for now, minus SYE, CV and upper rear adjustable arms.

Your pinion is 7.9 up. Your T-case is 10.1 down. You are within 3 degrees of each other, but you operating on a 20 degree slope, which means your U-joint at the diff is at 12 degree operating angle which is pretty high.

I have read 15 degree is max angle and that is for lower speed. Most OEM I remember won't run higher than 7 degrees of operating angle. And they really want 3.


If you lowered your t-case just a pinch more it will calm down some.

I already have a 1.5” tc drop. Do I need to drop it down even further?

 

[Midtenn]

It looks like you have adjustable upper rear arms in the first pic?

So as stated before rotate your pinion up a few degrees, and that may resolve it also for now. until you buy that SYE.....

I think some of the pictures are measuring from the wrong spot since I have all sorts of angles. If I measure at the balancer, it’s within 1 degree. However the slope of the driveshaft it still bad.

 

[Cross-Threaded-06TJ]

I already have a 1.5” tc drop. Are

I already have a 1.5” tc drop. Do I need to drop it down even further?

I think some of the pictures are measuring from the wrong spot since I have all sorts of angles. If I measure at the balancer, it’s within 1 degree. However the slope of the driveshaft it still bad.

Like @LieutenantJohnson said, all Jeeps are different and may stop vibrating from a different adjustment. Gear ratio and tire size/RPM at when it vibrates....

I believe what he and I are thinking is you could literally toss like 1 washer in-between each lowering spacer at a time and go road test it, and it may resolve it for now. Just with a fairly large T-case drop.

Or, it looks like in that first pic your upper rear arms are threaded and you could rotate up SLIGHTLY at the pinion. and try to massage the vibration out.

My take is the 10+/- operating angle on the Joints is your root cause. @JMT mentions a MML which when combined with rotating your pinion up to match that angle would reduce your overall U-joint operation angles. Just at the cost of pretty far flexed motor mounts and transmission mounts. I'm not sure how bad that is on rubber mounts, just saying I wouldn't like it. But would be cheaper than an SYE now.

A CV shaft, when the pinion is set correct, makes the U-joints in the Double Cardan your operating angle, which will be half what the slope is.

 

[Midtenn]

I’m following...unfortunately jb is oos on their sye.