I usually just get the bearings from autozone and it’s whatever their in store brand is.
Very likely bottom-feeder Communist Crap.
But even so, they shouldn't fail that often.
To set preload I spin the rotor forwards as I tighten the spindle nut and once I feel drag on the rotor I back the nut off till I can get a cotter pin in it.
So...you're grossly over-tightening the bearings. They've
probably still got preload when the cotter pin is shoved-in.
No wonder they fail.
Having failed the bearings, the races are damaged. They all have to be replaced; and driven-in smoothly and evenly without damage to the races...or the rotor/hub.
Follow the actual GM procedure for wheel bearing adjustment, (Example: Page 3C--11 of the '88 C/K service manual) and see what happens. Spin the rotor while tightening the nut to the
specified torque of 12 ft/lbs, instead of so friggin' tight the rotor has drag.
Back off the nut to "just loose".
Back off nut as needed from "just loose", but not more than 1/2 flat, to align cotter pin hole.
Having done it "by the book" a few times, I now do it "by feel", with the
final step being to remove all bearing clearance with two fingers turning the nut, then backing-off enough to get the cotter pin in. It's another way of assuring that I set my
free-play from "just loose" after having aligned the bearing rollers with higher torque.
Tapered Roller wheel bearings operate with a minimal amount (GM Spec for clearance is .001--.008, but nobody is going to actually measure it) of FREE-PLAY, not "preload". "Preload" is for 1950s-and-prior BALL wheel bearings.
For the record, the best/slickest/simplest/fastest way to pack wheel bearings is what is now sold as the Gearwrench wheel bearing packer, but which used to be sold by the company that invented the thing.
www.amazon.com/GearWrench-2775D-Hand-Bearing-Packer/dp/B0002NYDYE/ref=sr_1_4?crid=3H6W78BF64D2K
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Lisle has a competing product, and Amazon shows about a hundred brands of cheap-junk knock-offs.
There is a single thing I'd warn you about using this bearing packer. They tell you to place the inner bearing on the packer small-side down, the outer bearing small-side down on top of the inner, the upper "cone" part of the packing tool on top of the inner bearing. But then PUT A SHOP RAG OR PAPER TOWEL on top of that. Then put the whole works on the floor, step on the towel to squeeze the grease into and through both bearings.
That way the dirt on your shoe doesn't contaminate the grease.
I have two of 'em--one with Valvoline "red" grease for cars and trucks, one filled with marine "waterproof" grease for boat trailers.