Driveline angles and new vibration

[Judy 87YJ]

I had to raise my NP231 transfer case about 3/4” to get it off the skid plate which has 1 3/4” spacers. The two had rubbed a hole in the TC so I installed a new rear half casing. I still have a slip yoke and will upgrade “next bonus” to a SYE. Since I raised the TC, I now have low rpm vibration. My TC is currently at 7.2 degrees and pinion is at 12.5. Driveshaft is at 21. My research is telling me to put a 6 degree shim in at the axle which would be 1
Degree less than the TC ant 7.2. Anybody know what this will make my driveshaft and will it be too much? Am I correct on figuring the shim size ?

 

[Gilaguy23]

How did the pan rub a hole in the case? Trans mount collapsed or? Im no expert on how much is to much but having two end angles more than 1.5 degrees isnt a good thing.

 

[Pman]

Show us a pic of the angles please

 

[Judy 87YJ]

How did the pan rub a hole in the case? Trans mount collapsed or? Im no expert on how much is to much but having two end angles more than 1.5 degrees isnt a good thing.

I think the transmission mount wore out but it didn’t look it. It was spongy though. I replaced the stabilizer while I was there as well. More play than the new one.
I understand the differences should not exceed 3 degrees and it might have been there before the TC raise. Hopefully some one knows approximately what degree my driveshaft will be when I pivot the pinion from 12.5 to 6 degrees. If it will work, I’ll look into the SYE but that’s another day.

 

[Judy 87YJ]

Show us a pic of the angles please

Here a several. Thanks for time.

 

[Pman]

Those angles aren't terrible..remember the angles for a conventional driveshaft and a DC drive shaft are different. Im going to try and get Shawn from Tom Wood to jump over here and help

 

[machoheadgames]

Looks like a typical rough country lift which they ship with 6° shims which are only proper for a double cardan driveshaft and slip yoke eliminator setup. You need to change that pinion angle to be more parallel with the tcase output, so around 6-7°.

I can’t explain the tcase getting holes rubbed in it by the pan. If you get the angles right at the pinion you can probably put the tcase and skid back to stock height and fix that issue.

 

[Shawn at Tom Wood's]

There are two ways for you to get the angles right.
1. install a slip yoke eliminator and adjust the pinion so that it points towards the transfer case (in-line with the drive shaft).
2. remove your lift and lower the Jeep.

I know you said that option 1 is planned but not in the cards at the moment. I know that option 2 is not a realistic option. So what do you do now? Mainly you just have to accept that the angles are wrong and do what you can to get them as close to right as possible. In your case, I think that means leaving things the way they are. For the stock type shaft to work correctly, two parameters need to be met. One is that the transfer case and pinion are parallel to each other. The other is that the joint angle at each end is less than 10 degrees. If you ship the pinion down you will be making things parallel but you will be making the second thing, the joint angles, much worse. This is because you will be lowering the bottom end of the drive shaft thus significantly increasing the angle of the drive shaft itself.

More on that here:

Slip Yoke Eliminator Installation Purpose and Benefits

At Tom Wood’s Custom Drive Shafts, we're your go-to source for all your Jeep driveshaft needs. We offer high-quality 4x4 driveshaft products and components to fit various Jeep models, including the Jeep CJ, Jeep JK, JL, and others. One crucial component found on many Jeep types, such as the YJ...

4xshaft.com

You can also learn even more about proper geometry on this second page. There's a lot of overlap in the videos but the second one is more in depth about what works, when, and why.

Driveline Geometry 101

Driveshaft Angle Explained This video will demonstrate the proper angles for a drive shaft in a stock Jeep or Truck and how the rules change when you add a suspension lift. The video below demonstrates what is happening to the shaft at different angles, how improper angles can cause speed...

4xshaft.com

 

[Judy 87YJ]

Those angles aren't terrible..remember the angles for a conventional driveshaft and a DC drive shaft are different. Im going to try and get Shawn from Tom Wood to jump over here and help

That would be great!

There are two ways for you to get the angles right.
1. install a slip yoke eliminator and adjust the pinion so that it points towards the transfer case (in-line with the drive shaft).
2. remove your lift and lower the Jeep.

I know you said that option 1 is planned but not in the cards at the moment. I know that option 2 is not a realistic option. So what do you do now? Mainly you just have to accept that the angles are wrong and do what you can to get them as close to right as possible. In your case, I think that means leaving things the way they are. For the stock type shaft to work correctly, two parameters need to be met. One is that the transfer case and pinion are parallel to each other. The other is that the joint angle at each end is less than 10 degrees. If you ship the pinion down you will be making things parallel but you will be making the second thing, the joint angles, much worse. This is because you will be lowering the bottom end of the drive shaft thus significantly increasing the angle of the drive shaft itself.

More on that here:

Slip Yoke Eliminator Installation Purpose and Benefits

At Tom Wood’s Custom Drive Shafts, we're your go-to source for all your Jeep driveshaft needs. We offer high-quality 4x4 driveshaft products and components to fit various Jeep models, including the Jeep CJ, Jeep JK, JL, and others. One crucial component found on many Jeep types, such as the YJ...

4xshaft.com

You can also learn even more about proper geometry on this second page. There's a lot of overlap in the videos but the second one is more in depth about what works, when, and why.

http://https:/general- the SYE

http://

 

[Judy 87YJ]

Thanks a million for the expert response, Shawn! SYE it is. Pman, thanks for steering me right.

 

[machoheadgames]

This should be simple to fix, for the short term. Get the angles to parallel and let the ujoint operating angles be greater than they should be. It will wear the joints faster but for temporary it’ll be fine.

12° is not factory pinion angle. Factory is like 6°. If it’s at 12, then someone either rewelded the perches, or the springs have shims on them. Figure out which. Fix accordingly.

 

[Pman]

Thanks a million for the expert response, Shawn! SYE it is. Pman, thanks for steering me right.

Shawn has always been a huge help on the tj side of things I knew he would be helpful here as well. Plus if you have a problem pick up the phone and call they will answer!!

 

[Shawn at Tom Wood's]

This should be simple to fix, for the short term. Get the angles to parallel and let the ujoint operating angles be greater than they should be. It will wear the joints faster but for temporary it’ll be fine.

12° is not factory pinion angle. Factory is like 6°. If it’s at 12, then someone either rewelded the perches, or the springs have shims on them. Figure out which. Fix accordingly.

I am predicting that rotating the pinion down to match the transfer case will make things worse. This is because it will increase the angle of the drive shaft too, by about 4-5 degrees. That will increase the operating angle of the joint at the transfer case end from 14 to around 18-19. That is too much angle for the shaft to run smoothly, even if they yokes are parallel. Spicer says that the max operating angle of a single joint at 3,000 rpm is 5.8 degrees. This limit can be pushed a little with good success but tripling the limit does not usually work out well. The way things are now, the yokes are a few degrees off from being parallel but that pinion rotation helps to mitigate the driveshaft angle and the overall joint angles. It's not quite right for either the parallel or the less than 10 degree joint angle rules but it is only a little off for each instead of extremely far off for one or the other. Anecdotally, most people have better success with having the pinion raised a little in this type of scenario than they do if they keep the pinion at the 6 or so degrees that it would be stock. But, a lot of this has to do with dumb luck and how a certain set of parameters happens to play out in a certain vehicle. Perhaps rotating the pinion down would make things better in this specific Jeep but It might also prove to be a waste of time and money that only makes things worse than they are now. If parallel yokes was the only part that mattered slip yoke eliminators wouldn't be such a popular thing for lifted Jeeps. That is explained in better detail on the page in my second link above.

To the OP, if you want to try rotating your pinion down a couple/few degrees it might make things better. But as stated above it might also make things worse. You won't know until you try but as long as you know the risks of possibly wasting a little time and a little money on shims it might be worth a try.

 

[Shawn at Tom Wood's]

Shawn has always been a huge help on the tj side of things I knew he would be helpful here as well. Plus if you have a problem pick up the phone and call they will answer!!

I enjoy doing what I can to make information readily available to people and am excited to contribute to the YJ forum. I think that I and others (Jerry Bransford and others) have gone through and answered/explained just about everything drive shaft related by now on the TJ forum. This forum will give me the opportunity to put some energy into helping answer questions for a new audience.

 

[machoheadgames]

I am predicting that rotating the pinion down to match the transfer case will make things worse. This is because it will increase the angle of the drive shaft too, by about 4-5 degrees. That will increase the operating angle of the joint at the transfer case end from 14 to around 18-19. That is too much angle for the shaft to run smoothly, even if they yokes are parallel. Spicer says that the max operating angle of a single joint at 3,000 rpm is 5.8 degrees. This limit can be pushed a little with good success but tripling the limit does not usually work out well. The way things are now, the yokes are a few degrees off from being parallel but that pinion rotation helps to mitigate the driveshaft angle and the overall joint angles. It's not quite right for either the parallel or the less than 10 degree joint angle rules but it is only a little off for each instead of extremely far off for one or the other. Anecdotally, most people have better success with having the pinion raised a little in this type of scenario than they do if they keep the pinion at the 6 or so degrees that it would be stock. But, a lot of this has to do with dumb luck and how a certain set of parameters happens to play out in a certain vehicle. Perhaps rotating the pinion down would make things better in this specific Jeep but It might also prove to be a waste of time and money that only makes things worse than they are now. If parallel yokes was the only part that mattered slip yoke eliminators wouldn't be such a popular thing for lifted Jeeps. That is explained in better detail on the page in my second link above.

To the OP, if you want to try rotating your pinion down a couple/few degrees it might make things better. But as stated above it might also make things worse. You won't know until you try but as long as you know the risks of possibly wasting a little time and a little money on shims it might be worth a try.

Overall I agree that there really is no way to truly win when you’re stuck between lift and no SYE. The first thing I did to my YJ 10 years ago was a 2.5” lift from rough country. Broke high school kid and needed clearance for the 31’s that came on the Jeep. Hindsight, should have reverted it to stock rims and tires, but I didn’t. The RC springs come with 6° shims on them. I initially did not run a tcase drop. The vibes were absolutely terrible. Installed a t-case drop, which helped considerably, but it still was not right. I ran that way for about a month while I saved for SYE/DC shaft…I don’t think it would have worked very well longer term with the pinion pointed up 6° extra and the tcase pointed down. It made for an odd looking setup similar to the photos in this post. Eventually, I swapped to the SYE and double cardan, which with the 6° shims and deleting the t-case drop, was perfect.

After all I learned from that experience, I started recommending to others (who installed 2.5”ish lifts) to do a small t-case drop and 2° shims. Pretty much all of those have turned out well. I don’t know what their operating angles are - probably outside of the max. Maybe they need to replace joints more often. I don’t really know. I did only suggest this as a temporary fix. I figure parallel with higher angle is better than how it looks in those pics, because the way it looks is how mine was for a month and I really didn’t like it.

Overall should probably just leave the Jeep stock until a plan is in place to fix immediately, unless willing to park it after lifting.