CantDrive55

Hi all, I recently installed a 3" lift and am having Driveline vibrations. The leaf springs are 3.5" pro comp with the over load leaf taken out so it is at 3" instead. It came with 6 degree axle shims so I put those in however I think I may have made the angle worse by installing them? I was originally planning on a transfer case drop but now im thinking of removing the axle shims the leaf springs came with and see if that helps. I need feedback from you guys though as I know nothing about angles and where it Should be at, but I know it shouldn't look like mine.



Would the angle be better if I took out the shims? Or worse... Thank you.

I would also like to add that the u joints are strong and not loose or sloppy.

tedparis

Hi, I am an engineer and a program I worked on a few months back was finding pinion angles and U-Joint angles on some heavy duty trucks. It is important to minimize your U-Joint angle to reduce vibrations as U-Joints have a changing angular velocity as they rotate. As for your situation you need to make sure that the U-Joint angle at the transfer case cancels out the U-Joint angle on the rear axle pinion. In you situation I would recommend dropping the transfer case and either shimming the axle or lengthening the leaf spring shackles. What matters is that you adjust the angles to be PLUS OR MINUS 1 DEGREE OF ONE ANOTHER. The reason I say 1 degree difference is to keep your needle bearings active and prevent the formation of flat spots. This is common practice in the automotive world. Let me know if you have any more questions.

TRCM

Well, from the pic, the OP needs to remove shims from the rear axle, not add them. The angles at the tcase and the rear axle should be within 1 deg as you said of each other, but they should be opposing so as to cancel each other out again, like you said.

If he puts more shims in, or adds longer shackles, the pinion will point even farther up....moving the angles in the wrong direction.

If he drops the tcase, that will flatten the angle at the tcase, which may help, but it causes other concerns (motor mount stress, front d/s angle no get worse, shifter linkage may not work correctly).

He needs to measure the angles, and let us know what they are, then we can let him know what he needs to do.

It looks like he needs a 4 deg shim not 6 deg on the rear axle. This would pull the pinion down, and get the angles closer.

I am running a 6 deg shim with 4.5" lift and no vibes, but I do have a SYE also.

If you look at this quickie dwg, you can see what I am saying. You want the angles that should match to be the same.

Black is what you want...pink is what you started with, and green is what you get by the action listed.

(reminder, is you use a SYE, the dwg no longer works...different situation)

chizuck

Not saying your angles are right. but if you universals were in poor shape putting the extra stress on them would bring it out much more and cause a vib

TRCM

I didn't mention that cuz the OP said they were good, but that is also true.

Some other things that can cause vibes:
1) the driveshaft now being in a slightly different position within the tcase snout which can change the thrust on the bearing and the spot where it rides on the splined shaft
2) the u-joints working thru a different angle, even if they are good & tight


Have you checked for other things ?? I once had an ebrake cable come loose and it was hitting the wheel weight on the pass rear rim when I turned left.

caged

the new angle will make your u-joints angry. change u-joints and go from there.

TRCM

good one.........