quick Q about 3.73 install

copied from within 1st link below...read.
torque the fasteners to 70-85 ft-lbs. Check gear backlash with a dial indicator and magnetic base; it should be .008-.015". If out of this range, you'll need to get shims to move the differential assembly either toward or away from pinion to correct. The Ford service manual has a good table of shims and resultant change in backlash (You'll need a copy of this to ascertain the thickness change to produce the desired backlash change, as it's not a linear function.). Essentially, what you remove from one side will have to be added to the opposite side. Once backlash is within range, remove the shims and install .006" thicker shims on both sides. You'll have to drive these in; they keep the bearings loaded (Hint: Place the thinner shims in place first, then drive the thickest into position last). Check the ring gear run-out on the back face. This should be no more than .004". If it's more, then remove the diff assembly, rotate the ring gear relative to the case, reassemble, retorque, reinstall, recheck. Redo as required (I think I'm REtarded!). Once proper backlash and run-out are obtained, check the gear contact pattern using gear marking compound. Paint four to six teeth in three or four locations around the ring gear, and "drive" the diff assembly several revolutions by rotating the pinion (try and keep some friction on the diff assembly as you do). Check the pattern against the chart at right (or look at the Drive Train Page site listed). Adjust as required to obtain the desired contact pattern. Install the axles, c-clips, pinion shaft and fastener (torque shaft lock pin to 15-30 ft-lbs). Apply an 1/8" bead of RTV to the cover and install; add oil, install swaybar, tires, etc.



read thru these links it will help you...

http://www.corral.net/tech/drivetrain/gears.html

http://www.louisvilleoffroad.com/Ring-and-Pinion-Installation-sp-9.html

http://www.superstallions.com/tech/drive/gears/gears.html

good links

You are going to refill the rear end with gear lube and friction modifier, right?

Ideally you would use a dial caliper to measure backlash, and gear marking grease to observe the mesh pattern, as well as an inch pound torque wrench to measure the pinion preload. But you can read more on those things in the links.