Is my rear pinion angle okay?

If the vibes go way when you compress the suspension, that my be telling you that your pinion is likely a little too low when at normal ride height. Hard to tell from the pic, but it doess look a little low there.

if raising the pinion back up a little still doesn't fix it, it may also just be that the operating angle is too much.

This is what you're trying to cancel out by setting the pinion parallel to the t-case output.

14273_179_2.jpg


The problem is at some point, even if they're cancelled out so the pinion isn't being pulsed like a sine wave, is you still have the angular momentum of the body of the driveshaft that's speeding up and slowing down twice for every revolution it makes as it spins, and that change in momentum ends up getting dissipated as vibration felt in the driver seat. I played this game on my TJ trying to get the least possible t-case drop I could get away with, got there, and then the vibes came back after a regear because the driveshaft was spinning faster than before, so I had to do it again and the t-case drop doubled. That's about when I said screw it and ordered a SYE.
 
  • Like
Reactions: DuvelSteve
Hi there… Bringing back an old thread.

I added the UCF extra clearance skid plate to my LJR. Im using the stock tranny mount but do have an mml and adjustable uppers and lowers. After the install I notice pretty bad vibes that get really bad at speed when the throttle is pushed. I took some pictures of the angles and was hoping for some guidance in adjusting. Thanks Guys.

DF77E3CB-658A-4243-BD53-916C44F6D167.jpeg


3E96B7E9-D988-4697-9E7E-D8C2D189B42B.jpeg


C43A8726-B6B7-4A2C-B19C-A30F15C641F1.jpeg


9BE7FAB8-57D0-425D-BB21-958F96CBE849.jpeg


B03564ED-45E3-4E32-AD04-4E9C3E7F1781.jpeg
 
I took some pictures of the angles and was hoping for some guidance in adjusting.

Assuming it's just a tummy tuck and no additional lift, the LJR rear shaft should be able to handle the driveline angles.
Especially with the addition of the MML.
However, it looks like your rear pinion is pointed up.
It should be parallel to the transfer case output since you're using the oem (2 joint) driveshaft.
 
Like @LONGJP2 said, with that type of driveshaft, your pinion should be parallel with the TC shaft.

I have a 2.5" lift on my LJ, and recently installed the UCF Extra Clearance skid, too. I thought I would be able to get by with the OEM driveshaft, but the combination of the spring lift and the semi-tummy tuck made driveshaft angles too steep, with vibrations which I could not get rid of. I had to install an SYE and DC driveshaft, which took care of the problem.

It's worth trying to lower your pinion, but you may need a DC driveshaft to resolve it.
 
Thanks guys, I forgot to add that have the 2.5 OME lift. Im reluctant to lower the case because I raised everything up in order to get into reverse after I put the B&M shifter on.

I'm hoping to save a few bucks and use the arms. I'm just not sure what angles I am setting as a goal. I've read the pinion and the drive shaft should be 1-2 degrees apart, but I'm not sure if the Rubicon tcase changes things. Im thinking I can raise the pinion a few degrees up a few it will match the tcase.
 
Last edited:
I forgot to add that have the 2.5 OME lift.

Your lift plus TT is probably close to maxing out the joint's range of operation.
Start with getting the angles right.
Yes, the pinion can be down a little extra to compensate for movement when accelerating.
If you're still getting vibes, troubleshoot by lowering the TC / skid a couple washers at a time.
The vibes could also be coming from the driveshaft and needs rebuilt.
It's my opinion that the joints can get a wear pattern that will cause vibes when you change to a new operating angle.