Pinion Angle Question

Hey guys,
This is my first post on the board, but I've been reading through the board since I first got my XJ, and there's a wealth of knowledge in here. I'm hoping you guys can help me clear up my confusion with rear pinion angle. I've got a '98 XJ and recently installed a 3.5" RE Super Flex lift kit, and since have had vibrations at lower rpm's, and a grinding noise when I let off the gas. Here are my measurements....

Rear Knuckle - 7.5 deg up
Rear of Rear Drive shaft - 18.5 deg up
Rear Working angle - 11 deg
Front Knuckle - 4.5 deg down
Front of Rear Drive shaft - 18.5 deg down
Front Working angle - 14 deg

Now from everything I could find within the board and online, I want my rear working angle to be about 0.5 degrees less than the front working angle, which would mean I need 2.5 deg axle shims. But then I've also read that I want the rear working angle to be as close to zero possible, which would mean....11 deg shims?!? I've read most people are using 4 deg shims with this set up, I'm thinking I need 2.5 deg shims, but if you guys could clear up the confusion, it'd be much appreciated!

I'm guessing you are running a sye. if not do you have a TC drop installed?(you should be)

With a sye you want the pinion pointing as close to the same angle as the driveshaft as possible.

Hope this helps

If you have a grinding noise it is probably a bad u-joint or pinion bearings.

The grinding sound when you let off the gas is a drive line vib sound. It happens to mine decelerating in the 40-55mph range. Changes depending on how much crap I have in the jeep. Do an SYE or a transfercase drop for a quick fix. The newer 231 transfercases are prone to vib easier than my older 231. They have a slightly diffrent output shaft set up.

Good drive line configuration design has the pinion angle equal to the TC output angle. The objective is to have both ujoints at the same angle. So the angle between the DS and the TC shaft should be the same as the Pinion and DS. The tolerance for variation is dependent on the length of the DS. BTW it is not limited to vertical measurement but at any rotational measurement. If there is misalignment at any angle, it can cause vibration.

Thanks for the responses guys. I don't currently have a SYE installed, and I haven't yet installed a TC drop, I was hoping to alleviate my issues with just shims and save myself the ground clearance as well as $$$ for a SYE for right now. Seems like my best bet would be to go ahead and install the TC drop though, and hopefully this will cure up the vibes. Thanks again for your help guys.

snwboardxj said:

Thanks for the responses guys. I don't currently have a SYE installed, and I haven't yet installed a TC drop, I was hoping to alleviate my issues with just shims and save myself the ground clearance as well as $$$ for a SYE for right now. Seems like my best bet would be to go ahead and install the TC drop though, and hopefully this will cure up the vibes. Thanks again for your help guys.

Click to expand...

Just try to match the pinion angle with the transfer case output angle. That's for non-sye setups. You may want to go a degree or two down (pinion angle) cuz the leaf springs cause axle wrap which brings the pinion up a degree or two when accelerating.

For example, on my sye setup I run my pinion angle 3 degrees down from the driveshaft angle so it's like driveshaft angle is 14, pinion angle is 11. So when I acclerate, the pinion rises to about 13 degrees, pretty much perfect and no vibes.

Just my opinion!!!!!!!!
If you installed a RE 3.5" kit you are probably sitting 5+ inches high in the rear, Shims alone likely will not solve your problem.
I would go for a RE Hack & Tap SYE and a Late model XJ Front shaft.
I do not like TC drops, They stress the Mounts too much.

X2 on the hack & tap. It's cheap and works great. TC drops are crap and if you wheel it's the worse thing you can do. One good hit on your nice aluminum case and it's all over.

Thanks again for all the help guys. I'm thinking now that I will go ahead and go with the hack and tap solution. I wasn't really too keen on going with the tc drop to begin with, and if shims won't be able to cure the problem, might as well go the route that'll help offroad as well. As far as the ds....mine's a '98 AT 4.0, so the newest XJ AT front drive shaft is what I need with the hack and tap sye, is that correct? Thanks again guys.

I have a '96 with a 3.5" RE kit installed, and I got way more than 3.5" out of it. Measuring from the center of the rear wheel to the bottom of the factory fender flare, it should be 17" when stock. Mine is sitting now at 22" -- that's 5" over stock. Without a SYE, it was undriveable. I drove it home from having the lift installed, and parked it until I had a SYE in hand.

Without a SYE, try to get your transfer case output shaft and rear pinion parallel. If you install a SYE, set your rear pinion two degrees less than the driveshaft angle (to allow for axle wrap). With 6 degree shims, my pinion is 15 degrees and my driveshaft is 17 degrees.

M4Madness said:

I have a '96 with a 3.5" RE kit installed, and I got way more than 3.5" out of it. Measuring from the center of the rear wheel to the bottom of the factory fender flare, it should be 17" when stock. Mine is sitting now at 22" -- that's 5" over stock. Without a SYE, it was undriveable. I drove it home from having the lift installed, and parked it until I had a SYE in hand.

Without a SYE, try to get your transfer case output shaft and rear pinion parallel. If you install a SYE, set your rear pinion two degrees less than the driveshaft angle (to allow for axle wrap). With 6 degree shims, my pinion is 15 degrees and my driveshaft is 17 degrees.

Click to expand...

Same here, Even after driving around all last winter with 400Lbs of sand in the back it still sits at about 4.5" of lift.
I installed the SYE when I had 2" of lift, on my 01 the Vibes were terrible at 2". I went from a 2Deg (@2" lift) to a 6 deg shim after I installed the RE 3.5" packs.

My first Cherokee yielded over 5" of lift with the RE 3.5" lift kit. I do not have a SYE on it, but I did use a 1" TC drop. I had the same "grinding" noise you described, but no real heavy vibes.

I added a 2.5 degree shim recently under the rear leafs. Good investment. Try that. It's cheap and easy. Also get the TC drop if you dont plan on running a SYE and driveshaft (over $600 for a good setup).

Did you replace any of the driveshaft U joints at all or are they the stock 100K miles units? if not, that plus a slight TC drop would probably cure the noise prob, but the SYE is a better solution if you have the $$