AAAAAAAAAAAAAhhhhhhhhhhh the ol dana 35 wheel bearings.
OKay well tons of stuff can cause these baby'sto fail early, especially if they are not torqued properly.
Getting the pre-load on the bearing is tricky and doing it by the book often is not good enough, especially if you have larger tires.
They recommend torque the inner spindle nut to 35 ft/lbs, then back off 1/4 turn, then re-torque to 18 in pounds. Then install the lock washer and torque the outer nut to 150-180 ft/lbs.
This works okay but it is important to turn the rotor several times after each step.
I have also found that 18 in pounds (finger tight) is not enough for bigger tires, they will just come loose again. So I usually set the preload, back it off 1/4 turn then torque them down to about 15-25 ft/lbs. Yikes! That seems like a lot, and my bearings may not last as long torqued down this tight. Not a problem for me since I have to clean and re-pack them twice a year anyways due to big tires, road trips, water, and 4x4ing. So I use Timken bearings, keep a few extra grease seals around and I can re-pack my front bearings and clean the brakes up in about 1/2 hour per side..
Timken makes the best bearings for the D35, they seem to last twice as long.
Also a bent wheel or unbalanced wheel can cause all sorts of wheel bearing problems!!!! Towing is also hard on the bearings and a perfect alignment is necessary, or you will be on there re-doing the bearings every 3 months.
I have not had any negative side effects from running the inner spindle nut at 15 ft/lbs to date, with 31" tires, towing, and a lead foot.