I have just set up my 12 bolt (first time) and test drove it and I am hearing a whining noise from the diff. I installed a eaton posi unit and strange 3.73 gears. The gears meshed perfectly and the only thing I was a little unsure about on the setup was the pinion preload. I put the car on jackstands and got it in drive and listened to the rear with a stethascope and the only part of the diff that was making noise was the pinion bearing closest to the yoke where the driveshaft bolts on. All the other bearings and even the gears seemed quiet. Has anyone else had this problem? Does anyone know of a place to find a pinion preload procedure?Thanks for all the past help.

The procedure is in the GM overhaul manual and possibly up on some of the rear axle component suppliers web pages. But, if you are hearing a whining noise, the gears are quite probably not set up correctly and I would not recommend driving it until they are.

With only the pinion gear in the housing and new bearings installed, proper preload is when it takes 20-25 oz-in of torque to turn it. Getting the proper depth on the pinion gear is the most critical and time consuming part of the job.

For the differential carrier side bearings, whatever shims it takes to remove all the side play (a snug fit) add .010" total.

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Dave
My 65 Elky & 2002 Camaro SS (http://home.attbi.com/~bates150/images/dad/elky_ss.jpg)
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Richmond Road Race 5-Speed, 3.07's

Your backlash should be around .010" also.
Sometimes the pinon have very slight burrs or sharp edges on them. I usually take a small sanding disk and de-burr the pinion teeth first.
This has helped me in many setups. There are some gear sets I have had that no matter what you do, they whine. Becomes more of a problem with the steeper gears