You need to measure preload on the bearings
before you take things to bits, then you torque the pinion to the
minimum setting (usually ~180-200 pound-feet) and check preload. Continue to torque in small increments until your bearing preload is within the rage given in the manual (I'm working on my axle pages still - but you can get torque figures on my site. Link in sig.)
Note that there are two different preload ranges - for new bearings, and for used bearing (or, for "overhaul" and "service," if you prefer.)
If you enjoy munching pinion bearings, preload ain't important. If you prefer to not have that "growling whine" from a failed pinion bearing, you will want to check.
If you're going to service your axle
even once - get an inch-pound torque wrench, either beam style or dial style. While "micrometer" or "click" type torque wrenches are quite useful, they're
useless for measuring preload on rotating assemblies. A beam style torque wrench is relatively inexpensive (no moving parts,) but a dial style is what you want if you're doing this a lot (and they get quite spendy.) I'd suggest a beam style for the casual user...
Torque wrench types:
Beam Type:
"Click" type (also called "micrometer" type or "microtork"):
And the "dial" type: