I had a set of Motive 4.10's installed on friday, and picked the car up as the shop was closing for the weekend. Having done this job in the past and hating it, I decided to farm it out. They were the long P/N # ( I was told these were OEM spec ) I asked the installer to put them in on the tight side of the lash spec. New carrier and pinion bearing too. Anyway, friday night I followed the Motive break-in procedure. and was surprised how silent the gears were. Sat morn we were going to scan the car, but before we headed to the highway, I wanted a "preview" of the changes from the 3.42's. From a low speed roll, I squeezed the throttle hard in first and it hooked, pulled second, and then let off the throttle at about 5000 rpm. I threw it into neutral to coast down for a turn, and I was greeted with a loud whine that was not there before the launch. Not a squeel, but more like the sound of a dry bearing at speed. It's most noticeable on coast. I limped it home in first (about 1/2 mile) there was no clunking at all. The shop doesn't open 'til monday A.M. so I'm guessing 'til then. I jacked the car under the centre section, and listened to the various bearing locations with a stethescope, but I couldn't isolate it. There is no play in the pinion, either in/out or side to side. Pinion angle is 1 deree down, but shouldn't matter.

So that's my story, I'm thinking they didn't have enough pre-load on the carrier shims, and the carrier shifted to one side. There was a little lash heard, but you can't tell without opening the diff.

Any thoughts ? suggestions? too what happened. Has anyone else experienced a similar noise here ?

Edit: anyone familiar with the factory carrier pre-load spec. ? I believe it's .010", but don't remember if that's per side, or o-all ?

Thanks

 

Well the shop increased the pre-load on the carrier to .008" per side and re-adjusted the back lash. One trip around the block, and the prob re-appeared, and the lash had opened up. Opened rear end again, ring gear looked fine, but pinion had excessive wear. Turns out the heat treating was wrong on the pinion, Motive is replacing them.