I am building a Dana 80 rear for a pulling truck. I installed a new locked carrier, 37 spline axle shafts, and a new ring and pinion. I have all of the backlash adjusted correctly as indicated in the manual. When I torque the pinion nut to 450 ft lbs as indicated the pinion turns extremely hard. In more reasearch I have found that the pinion should rotate by itself with a force of 10-35 inch lbs. I have to grab the yoke with both hands to get it to turn. What shims am I missing or do I have them installed incorrectly. How do I lessen the pre-load on the pinion. Thanks in advance.

 

Did you lose a shim from beneath the outer pinion bearing? Pinion preload should have been set before installing the dif case and ring gear.
However, if you have a excellent pattern on ring and pinion you might try the following.
Remove pinion nut and pull (not beat) the yoke. Now try getting outer pinion bearing out (Lucky if you do). Increase the shim pak thickness by .002 or .004 inch. Manual specifies .001 shim increase will reduce rotating torque of pinion by approx 8 inch pounds. Reinstall in opposite order and torque nut to 440 ft lbs according to my 2000 svc manual. All bets are off is differential is still installed and not with proper preload.
This job is not for the faint of heart.