Welcome to the thread guys! Thanks for the support and enjoy the show, haha

Started taking measurements for the rear axle shim install tonight. Stopped by Harbor Freight and picked up a new toy:


If you recently tuned in, basically one of the requisites to installing a SYE is to adjust the pinion angle of the rear axle so that it is inline with the driveshaft, pointing towards the transfer case output yoke. One way of adjusting the pinion angle of the axle is to install axle shims.

Determining the appropriate axle shim requires a coupe angle measurements and some basic math. First thing I did was to measure the rear drive shaft angle. It was found to be 18 degrees.


Little closer up...


Then, I unbolted the drive shaft from the rear axle to measure the pinion angle. Since the pinion is actually contained in the differential housing, I measured the angle at the differential's yoke. Technically, the surface of the yoke is at a 90 degree angle from the pinion, but my angle finder had 2 edges. If your angle finder has only 1 edge, then all you have to do is add or subtract 90 from your answer.

Here is what the measurement at the pinion looked like. The angle was found to be 8 degrees.


As previously mentioned, the pinion should ideally be inline with the drive shaft/pointing towards the transfer case yoke. Thus, subtracting the drive shaft's angle from the pinion's angle will give the difference/shim size required to line up the driveline.

So, 18-8=10 degrees of shim necessary.

However, it's my understanding that when calculating shim angles you should take into account the effects of axle wrap. Axle wrap is essentially a fancy term for axle movement, such that happens during acceleration for example. This movement can increase the pinion angle by as much as a few degrees. To compensate for axle wrap, it is recommended to go with a shim that is 1-2 degrees less than the calculated number. So, 10-2=8 degrees of shim necessary for proper driveline geometry.

That's basically all I did tonight, just wanted to kind of report on my work and see if anyone out there agrees/disagrees with my methodology or calculation. Honestly, I kind of feel like 8 degrees is a bit much.... but it's hard to refute some angle measurements and basic math. My lift kit is advertised at 4.5'' but I'm sitting closer to 5.25'' in the rear, perhaps that is a factor.

Anyway, if anyone has some advice/recommendations to throw out I'd appreciate the input. Otherwise, I'll be ordering up the 8 degree shims and I'll just have to see how it turns out.

 

This is an awesome thread. Very educational!

 

Thanks bud, I'm learning as I go.

 

Purchased some axle shims on my way home from work today. Did a little more research and deliberation and after quite a bit of trigonometry finally decided on 6 degree shims.

In an earlier post, I had calculated the difference between the drive shaft and pinion angles to be 10 degrees. Subtracting a couple degrees for axle wrap brought me to 8 degrees. Further research revealed one other component to the equation, essentially that when you change the pinion angle it concomitantly changes the drive shaft angle. Basically, by moving the pinion up you're also moving the drive shaft up and thereby reducing the angle of both simultaneously (not independently).

So, after a little trigonometry I settled on 6 degrees. I'm planning to do the install this weekend, possibly even tonight if I get some time. I'll just have to wait and see if I did my math right.

In the meantime, here's what I bought...

6 degree shims and new 5/16'' center pins


Checked out the angle, just for fun with my new angle finder... The shim's angle is spot on, but the table I'm using isn't perfectly level so it's off a fraction of a degree.


Also, before anyone points it out, yep... they're aluminum. The shop I went to didn't carry steel shims. I'll just have to keep an eye on them. I don't anticipate any troubles though.

 

Let us know how this goes, I know my pinion angle is way off and I need to get around to shimming the axle. This might be a little added motivation!

 

SUBSCRIBED, Absolutely great thread. great build and write ups, very informative, keep up the good work, great looking rig

 

Wow...This is a great thread. Its like having step by step instructions on how to build a Jeep. Thanks for doing this. I'm subscribed.

 

Thanks everybody!

The axle shims were a fairly straightforward install. I did both sides simultaneously, so some of the pictures are from each side.

Support the vehicle on jacks stands to allow the rear axle to drop.


Remove the wheels to expose the worksite:


Remove the u-bolt nuts:


Remove the leafspring retainer plate:


Lower the axle a bit to allow some separation between the spring perch and leafspring. Also, this is a good time to apply a couple c-clamps to keep the leafsprings together after the center pin is removed in the following step.


Remove the center pin:


Install the shim and new center pin. This was a little tricky because the axle would not drop enough to slide the new LONGER center pin in. However, I tugged on the leafspring and pulled it out away from the body a little bit which allowed enough room to get everything in place. And yes, I ended up having to move that c-clamp a little further to the left to make room.


Now it's time to reassemble. I started by jacking the rear differential up until the spring perch contacted the shim. At that point, in order to get the axle lined up properly you'll have to use another jack to raise the pinion up so that the spring perch will properly seat on the new angled shim. Here's the 2 jacks in action:


Once everything is properly lined up, just bolt it all down. I was in the process of torquing down the u-bolts here. You can see the shiny new shim.




Here's a couple more shots of the final product:




Driving impressions and new angle measurements to follow this post. And of course a couple pictures too.

 

Alright guys, got around to taking some new measurements from the recent pinion angle adjustment with the 6 degree shims.

The adjusted drive shaft angle went from 18 to 15 degrees from horizontal:


The new pinion angle went from 8 to 13 (90-77) degrees:


This is what the final product looks like:


I now have only 2 degrees (15-13=2) of separation between the pinion and drive shaft. The old setup was 10 degrees of separation! I'm real happy with the result. All-in-all... I am totally vibration free from the driveline.

By the way, I'm going to Bundy Hill Off Road Park tomorrow!
I will try and get some pictures of my rig in action and report back.

 

Just screwing around a little with paint.... kind of shows the before and after difference.

Before shims:


After shims:

 

i just spent the last hour and a half of my night reading this entire build. I also plan on running a 4.5" lift more than likely rough country, i already hav ethe 32x12.5x15 pro comp mud terrains on pro comp 15x8 i snagged for 50$ with 80% tread (they need a little cleaning thats all =]) Your build is my official dumbys guide to.

 

Your build is great. I like everything you have done. This is the second build I have read, but I have read more of yours. I got my xj this last spring and it had a hack job of a lift, And I felt what a death wobbbbvbbbllllllleeeeeee felt like before I knew what it was. I like taking lots of pics so I ll start a thread and show ya mine. I am in Mt Morris, and never been to the mounds.

[IMG]file:///Volumes/Srg%20%231/Me%20faces...../Favorite%20cars/Car%20in%20my%20past/Rocky%20the%20Jeep%20&%20part/100_0591.JPG[/IMG]

 

Shout out to another MI jeeper!!!!!!

Mud, it's not just wet dirt.....it's a way of life!

 

Great build!

 

An hour and a half well spent I hope? $50 is a great price! Good score.

Welcome to my thread. And yes, please snap a lot of pics during your build! I am fairly new to Michigan, moved here from Ohio... so I haven't had a chance to make it out to the Mounds either.

Thanks guys!