I have found lack of lube in sealed ball Chinese bearings a few times now,loose tolerances and grit left in the bearings during assembly. I ordered some micro ball bearings that I use in clocks and I got one batch that were rough as a cob. I popped the shields off one and inspected it under a microscope and the balls weren't even round,looked like they were made of slag.
This post from 2012 is from the “SilveradoSierra” forum. Never done it, but interesting.
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You know on the more modern trucks they have unitized hubs on them? The hubs only have dust seals in them and enough grease to keep them running for a while but its set up to fail. Well, people think you cant pack them. Wrong. You can go to NAPA and buy their ...
chrome air blower with the rubber tip. All you really want is the tip. Unscrew it and put an 1/8" pipe coupler on it. Take the grease fitting off of your grease gun (hand pump grease gun not air) and thread the coupler/tip on to it. Now take your vehicle apart and pull the ABS sensor. Use Kendall Super Blue 427 grease. That looks like what is in every bearing I have taken apart. Dont mix another grease. When you get the sensor out, put the rubber tip in the sensor hole and start pumping. Now you have a seal on the inside and outside. that you need to watch for grease. Pump until you just see like a sweat coming out of the dust seal, not oozing out mind you, and stop pumping. You have to keep looking at both seals because one will let it out sooner than the other. As a rule of thumb, a 1500 takes about 32 to 36 pumps on an average, a 2500 takes anywhere from 65 to 80 pumps. Once you see the grease at the seals, Remove the rubber tip from the abs hole, rotate the hub one revolution and let the hub push out some grease thru the sensor hole. Now take a screwdriver and go in the hole, angle it so its going against the direction of rotation, till you hit the commutator inside. When you feel it, lift the screw driver up a little and rotate the hub so more grease comes up the screwdriver. Now finish cleaning the sensor hole by pulling as much grease out as you can and install the sensor. You have just packed your sealed hub. This works with any vehicle that has the abs sensor in the hub and any make. There are pictures available at”(link)
I deleted the link^^^as it doesn’t work anymore.
www.silveradosierra.com