I don't think air in the fluid would cause that. It's something mechanical at the wheels.
BTW, GM used the same brakes on 1/2 tons from 1951 up thru about 1972, so should hardware kits and other parts should be readily available at your FLAPS.
Like Phil said, In the service manual, it says under brake shoe replacement:
11. Centralize brake shoes and set anchor pin, then adjust all brakes and cables.....
The instructions for setting the anchor pin are in items 17 thru 19 on page 5-12 of the 48-51 service manual.
Since we changed only the wheel cylinders during this round of maintenance, it stands to reason we might have to adjust anchor pin. I never consider that before. Will definitely give it a go!
