Okay, bear with me. Performed a gear swap and only achieved 12 in/lb preload on pinion (new bearings). Test drive revealed lots of decel noise, which I now know is insufficient pinion preload, as I neglected to differentiate between new and used bearing specs. Disassembled and got 4 in/lb at pinion nut (with carrier installed, but axles removed). Obviously not nearly enough preload. My question is, since the bearings now have about 75 miles on them, should I use new bearing preload spec (25-35 in/lb) or used bearing spec (12-15 in/lb) on reassembly.

 

Go ahead and set it to nearer the new specs. 25 in-lb min.

Don't forget, the carrier adds torque, and the pinion seal. If you're trying to measure pinion preload with those installed, you're going to come up with GARBAGE; specifically, way too little preload on the pinion bearings themselves.

This is one reason I like a crush sleeve eliminator... the preload can be set without the seal being there, then disassembled and the seal installed, then put back together at EXACTLY the same preload.

Likewise, your carrier bearings should have preload as well; LOTS of it. I like to set them up with AT LEAST .010" (.005" more shim than will just "fit" on each side) and preferably as much as .010". I don't think it's even possible to get "too much" on those.

 

Thanks. I picked up a crush sleeve eliminator kit to use this time around.

 

I agree with Sofa's recommendations. Set up the pinion preload with the crush sleeve eliminator and no pinion seal and no carrier installed. Once you get your correct measured preload, reassemble with the pinion seal and re-torque the pinion nut. Then, remeasure the pinion preload drag and that becomes the zero baseline for the carrier preload. Install the carrier and shim the carrier bearings to preload them. If you want to measure the carrier bearing preload, once assembled with no axles installed, measure the pinion preload again, subtract your "zero measurement" and multiply by your gear ratio. That will give you the measured carrier bearing preload.