Wobbling rear wheel/s

[slowboy]

I had my '72 GMC C1500 on jackstands while doing TH350 transmission filter and gasket change. After I got done and put transmission fluid in I started truck and was going through the gears. While doing so I noticed back driver's side wheel was spinning, but was wobbling.
I know the wheel and tire is ok because I had the wheels powder coated and when the tires were remounted they balanced out good.
When I set the truck down on the ground and drove it I didn't notice any kind of rearend shake or shimmy.
Can anyone tell me what/why the wheel was wobbling while on stands and what needs to be done to fix it please?

Thanks in advance y'all!!

Keith [slowboy]

[kwmech]

Wobbling how? side to side.........up and down?

[HO455]

Several things to look at.
Is the wheel seated completely on the drum? (Assuming drum brakes)
Is the drum completely seated on the axle flange?

If all that is good then it's time to check to see if the axle is bent. Remove the tire and brake drum. You will be checking the axle for run out. Ideally using a dial indicator but a stiff piece of heavy wire will work.

https://youtu.be/1w21GwZXmZ4?si=4fBLJOPujJMh1TgJ

Attach the wire to the axle, (clamping it will work as long as it is secure) then bend the wire so the end is pointing at the axle flange as close to the outer edge as you can without touching it. Have someone rotate the axle slowly while you watch the relationship of the flange and the end of the wire. If the axle is straight and true the distance between the flange and the wire will not change. If the axle is bent you will see the wobble again but on a much smaller scale.

If this shows the axle to be true its time to take the wheel to the shop for another look at it.