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Pinion angle shim math

R

Ronniexj

NAXJA Forum User
Location
MT
Hey guys, I'm about to order degree shims after installing a lift, SYE and CV shaft for my XJ. And wanted to make sure I did the math right.

My pinion angle is 7.5 degrees on the face of the yoke(checked both sides).

My driveshaft is at 19 degrees.

19shaft - 7.5pinion=11.5 degrees;

11.5 - 2 degrees for pinion pointing downward= 9.5 degrees of shim?

Which only 8 degree shims are made and my springs have not settled yet, so I was going to call it 8degrees and add a sand bag or two in the back to help squat it in the meantime.

Does this sound right?


SPECS:
97 XJ, 4.0, 231Tcase, AW4, new RE 3.5 SuperRide with full packs, CV driveshaft and RR SYE.
 
2*- 4* of shim sounds about right for 3.5" of lift. I don't think you are measuring the right stuff, or maybe you aren't doing the math right.

Go here - www.4xshaft.com/techinfo.html - and do some geometry, and slope vs. angle, research.
 
I did the research and I took the slopes correctly.

However no article that I have seen gives an explanation of a formula after the slopes are taken. Only that the pinion needs to point 2* or so below the TC output.

If I was re-welding the spring perches this would be enough info to set the right angle.


It doesn't identify how much 1 degree of shim on the pinion changes the driveshaft angle to come to a shim amount. They are proportional.

If I add a 6* shim and it changes the driveshaft angle 3* then I would need to calculate 9 into my formula:

19* driveshaft- 7.5 pinion=11.5*

11.5-9 (6 shim and 3* amount of change to the driveshaft)=3* the pinion would point downward.
 
I didn't see how much lift you're doing. I have about 4-1/2 or 5 inches and 8 degrees is just right, though your results may vary.

One thing to keep in mind is that if your lift is going to include shackles that also rotates the axle a bit. The longer the shackle the more rotation.

And one thing to watch out for, I originally used off the shelf 8 degree shims and soon realized my u bolts were coming loose. I'd tighten them and they'd get loose again. The wedge nature of the shim wants to work itself out over time, shearing the spring center pin as it goes. I had to machine my own custom shims with a hook on the end to prevent them working their way out. I've always been surprised that I've never read about anyone else having this issue.
 
The lift is a RE 3.5, atleast 4" actual. I'm running factory hangers, and my measurements are post install of the lift.

I've got 6 and 8 degree shims on the way, I bet the 8's will be way off but the 6's should be about just right so I'll start with those.

It just depends to what extent the shim amount changes the driveshaft angle.

I'm also running a brand new Engine & Trans mount which I think may be pushing my TCase up further than alot of peoples setups.

Thanks for the tip on the u bolts, Ive just got mine snugged right now because I cant drive the jeep with this pinion angle. But I'll watch them.
 
Shimming the axle changes the pinion angle, not the driveshaft angle. The goal is to point the axle pinion at the T-Case output, reducing the operating angle of the single u-joint at the axle end of the driveshaft.
 
Tim_MN said:
Shimming the axle changes the pinion angle, not the driveshaft angle. The goal is to point the axle pinion at the T-Case output, reducing the operating angle of the single u-joint at the axle end of the driveshaft.
Click to expand...

If what you're saying is true then rotating the pinion 45* would not affect the driveshaft angle. But we know that not to be the case, because they are tied together. A change to one angle will affect the other angle.

http://www.4crawler.com/4x4/CheapTricks/Driveline-101.shtml

"

  • If you have a double cardan drive shaft, you want the end with the single cardan joint to be at right angles to the drive shaft itself. So, get the drive shaft slope and set the pinion flange to be at a right angle to it.
    • So determine the exact angle, find your driveshaft angle from horizontal and then set the pinion flange to the same angle from vertical
  • You may need to repeat this process a time or two if starting from scratch. As you tilt the pinion up, the distance the driveshaft has to drop from the transfer case is decreased, making the angle a bit less than measured un-tilted.
    • For example, when I installed new springs on my Toyota 4Runner, I decided to use a CV-style rear driveshaft. I used 3.5" longer than stock rear spring shackles to accommodate the longer springs, this gave me about 6° of tilt, but I measured and determined I needed an additional 8° of angle. After installing the 8° shim, I found the pinion is now tilted up a bit more than the driveshaft. I therefore designed my own steel shim at 5° to set the pinion 1°- 2° below the driveshaft angle to correct that problem.
    • What I didn't account for with the double-cardan setup is that as you tilt up the pinion, you are raising the pinion end of the driveshaft and thereby decreasing its angle.
    • I assumed this would be negligible, but I was wrong.
    • On my axle (a Toyota mini-truck axle, 8" ring gear), it is approx. 11" from the axle centerline to the pinion flange. If my driveshaft is about 44" long, then there is an inverse ratio of the respective lengths to the angle change. In this case, for every 4° of pinion change, there is 1° of driveshaft change.
    • In other words, if you need a 5° angle change, move the pinion up 4° and this will drop the driveshaft angle 1°."
 
I'd put the 8 degree shims in and see how things measure up. It's hard to say for sure how much the driveshaft angle will drop. Depends on length of driveshaft among other things.

I'm guessing you have a 8.25 axle. I believe factory is 7-7.5 degrees on the pinion angle.

My 97 has the 8.25 and my 01 has a D35.

When you rotate the pinion up keep in mind that you're fill plug is going to go down so you should take into consideration getting enough fluid in there. Also, some say the ring gear throws enough oil to keep the pinion bearings lubricated while others tell of stories of trashed pinion bearings from high angles.
 
8 degrees is a ton for only 3.5" or 4". Can you post pics ? You have the pinion 2-4 degrees under the ds and to account for axle wrap under acceleration. Post pics of what you are measuring with your angle finder in there. You want to put a socket on the u joint after you get it straight up and down. So you can throw some longer shackles on and that will point your pinion up too
 
I have the same problem. However I welded my perches at 4* when I did my 8.8 swap do I had to add 8* shims.

To be honest you should just cut and weld new perches on and check your shock mounts too. They may bind up. I've never had good luck with shims. They always come loose
 
Ronniexj said:
..... move the pinion up 4° and this will drop the driveshaft angle 1°.
Click to expand...

I do not know is this statement is true, but I do know how to fix things.

2*-4* is the typical amount of shim needed for an SYE and approximately 4 inches of lift. 8* is excessive.

Installing extended shackles has the same effect as shimming, the pinion nose rises.
 
Last edited:
Tim_MN said:
Installing extended shackles has the same effect as shimming, the pinion nose rises.
Click to expand...

I've never seen this explicitly stated before, and, at first I was like, "whaaaaa?" But now that I think about it, it makes a lot of sense.

I've also been wondering where my driveline vibes are. I lifted mine about 3.5 and I expected to have vibes, but I'm still waiting for them to show up. Wonder if the fact that part of that lift came from extended shackles might explain that. Maybe?
 
Alright guys I got my 6*, 8* and longer studs in the mail today.

I jumped right for the 6* and got them installed a few minutes ago, here's my findings:

Driveshaft angle is now sitting at 17.5* and pinion is 14*. I'm going to call that spot on as my lift has 0 miles on it.

Take from this as you will, I got only about a 30% change on my driveshaft angle relative to my shim amount. But take note, shimming the pinion will affect your driveshaft angle.

Hopefully this helps someone else when they try to calculate their shim. In my case the standard 4* shim for a 4" lift is not appropriate.


Again here were my previous angles: 19* driveshaft, 7.5* pinion.

97 XJ, 4.0, AW4, 231, 8.25c, RE 3.5 SuperRide, factory shackles, Rugged Ridge SYE, Driveshaft Direct rear driveshaft.

Thanks for the input guys.
 
It looks like I spoke too soon. I've still got bad vibes.

I took the jeep for a ride with the 6* shims and still had bad vibes at 25mph.

I took those out and put in the 8* shim, vibes are still there but not as bad.

I tried switching the front driveshaft to the rear and that didn't change anything.

My slopes about 17* on the drive shaft and 16* on the pinion.

Anyone have any suggestions?
 
Are you sure you are measuring the pinion angle correctly?

I can believe the driveshaft angle is 17 but I'd guess it to be a little lower.

A quick and dirty way to measure pinion angle is to put the angle meter on the two side bolts of the differential cover and subtract from 90.

I'd also look at the transfer case side of things and make sure everything is tight.

I know when I first got my Jeep the rear output shaft of the transfer case had some movement to it. Turned out it was bearing in the speedometer housing moving around in the housing a little. With the new main shaft/SYE when I move that shaft the entire transfer case moves.

You might just want to put the rear end up on jack stands and run it at idle and see how that driveshaft looks when its spinning.

If you really need to run this high of an angle, for longevity, its probably time to look at doing something about your shock mounts. They could be as much as 3" different side to side. This can cause binding and will egg shape your drivers side lower bushing. JKS and Ruff Stuff have weld on solutions, or you could re-weld your shock mounts. (once you get all this figured out)
 
I put it up on jackstands and I've got a pretty nasty wobble at my CV joint. I removed the shaft and it looks like maybe* my yoke wobbles slightly aswell. But its very hard to tell.

Link to Driveshaft video, watch close

Both the new driveshaft and factory front shaft wobble, everything is tight.

I pulled the yoke and watched the shaft in the tcase spin, its seems true. There is no movement of the shaft itself. There is a little slop between the splines of the yoke and shaft until it is tightened down.

But this seems to be where my vibration is coming from for sure.

Any ideas? Do i pull the yoke and check for run-out on the machining?

It looks like I can go back down to the 6* shims for sure, my driveshaft and pinion angle are about the exact same.

10689857_940708972623570_3954874376701313789_n.jpg


Driveshaft 15.5*
10671228_940709065956894_6009764244457246190_n.jpg


Pinion 15.5-16*
10405252_940709015956899_5691583862293197215_n.jpg



TCase about 4*
10659353_940708932623574_3466077095958700407_n.jpg
 
Last edited:
Its not unreasonable for the yolk to have end play until it is tightened down to spec.

I can't bring up the video.

I think you'll be fine with 6 or 8 degree shims.

As an example, when I first put my SYE in I left it 3.5 degrees off at the pinion and have no vibes.

It seems like maybe the transfer case side is the problem from what you are saying.
 
Its not unreasonable for the yolk to have end play until it is tightened down to spec.

I can't bring up the video.

I think you'll be fine with 6 or 8 degree shims.

As an example, when I first put my SYE in I left it 3.5 degrees off at the pinion and have no vibes.

It seems like maybe the transfer case side is the problem from what you are saying.
Click to expand...
Try this link for the video: https://www.facebook.com/video.php?v=940713655956435&l=8733741761267707337

The rear leafs seem to have settled a little with a full tank of fuel in it and driving it for a few miles, I'm going to take out the 8* shims and throw in the 6's.

It seems as though it has something to do with the tcase. Being that I installed a full SYE from Rugged Ridge and the output bearing is new and I had no vibes to start when stock with the new motor/tcase mounts I am suspecting something with the SYE kit is bad.

I put in an order for a JB SYE and I will be sending the RR kit back. I don't know what else to try at this point.

I will probably take my driveshaft in tomorrow to have it checked/balanced just to eliminate that 100%.
 
Last edited:
I would pull that 8* shim out and put the 6 or a 4 back in. You want the yoke down 2-3 * below centerline.

And yes, it sounds like you're SYE is messed up.
 
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