Topic: Strange Vibrations

[elnino]

After installing a used 4.56 ARB 8.4 third, and doing rear axle maintenance, I have a vibration that is not present except right at 27 and above 50MPH and ONLY on deceleration. Putting the truck under load completely takes care of the problem. Its a vibration and a noise like going over rumble strips. Its especially noisy because I am running a solid carrier bearing. I am not sure where to start, driveshaft vs. third.


The pinion angle is probably in the negatives (as in practically pointed down). There was a super small degree shim that I pulled out, but can that small of a difference in pinion angle make noise? Does it sound like  any type of driveshaft or even transmission tailshaft issue? Its not wheel bearings, tires, balance. Its somewhere between transmission and rear axle

I'm starting to think it could be runout in the ring gear? Would a shop charge less to double check the third or should I just live with it and regear down the line?

Thanks in advance!

[yotatough]

I was getting vibs like that when my pinion nut came loose I put blue lock tight on it and it came loose again, I put red on it and its fine now.

[Rocksurfer]

Pinion nut, I also have had that happen. The pinion is held up on acceleration but drops on deceleration and will run against the carrier and will eventually start grinding against it.

[elnino [OP]]

Cool, I really appreciate the replies. What is the proper torque to put on the nut?

[yotatough]

I think it depends if you have a crush sleeve or a solid spacer, I think. I would just check it first and see if it's loose at all, mine was hand tight when I checked it.

[crazykooter]

If its the pinion nut on the 3rd then theres a problem.  If you have a solid pinion spacer then torque is 125 ft pounds.  You MUST BE 100% sure its a solid spacer tho.  If you have a crush sleeve spacer then imo your gonna have to pull the 3rd and reset the preload to 15 inch pounds.  This is done by tightening the pinion nut little by little till you get the correct preload.  The preload is measured on the rotation of the pinion.  So you need a inch pound torque wrench to do this accurately.  Others my say line up the old spot were the nut was but thats a bad way to do it since it could have backed off more then one turn.  Do it the right way and save your gears.

If its the nut on the output of the tcase then you can torque it till its tight then dent the nut completely.