when setting up a carrier, is there a way to test how much carrier bearing preload you have? if it matters im installing it in a 3.73 posi in my 69 12 bolt. thanks

I use a small ball peen hammer to tap the shims in. If I can pull the differential back out by hand I will add .002 to it untill I can't pull it out by hand. This is with new bearings. Used bearings shouldn't be quite as tight. Be carefull not to damage the housing by gouging it with the shims when you tap them in.

That's a good rule of thumb, you should have to pry it out with some amount of force if the preload is correct. The technical spec is approx. .008-.010" of preload with new bearings. If you've got a bunch of shims, shim it until it slides in with no back and forth play and no preload, then add .004" to .005" to each side. If the gear backlash needs to be adjusted at this point, subtract a few thousandths from one side and add it to the other.