Loose manual hubs and ABS

Need some refreshing on manual hubs. Tinkering on a diesel V2500 Suburban which has manual hubs. Noticed that they are not tight, but when I put an Allen wrench to the cap screws they are tight. As it was the last century when the last time I had manual hubs apart I don't remember how they are assembled. What do the cap screws screw into in the hub? Is this indicative of an expensive problem? Truck also has ABS on it and I am wondering about the brake bleeding process. The Haynes manual is kind of vague on the "tooling" needed for the valve that needs to have the pin held to get things to bleed properly. Right now the brain box for the ABS is unplugged and sitting in the cab with no real plans on putting it back. After almost crashing my 94 Suburban because of a failed ABS system I don't really trust them any more.
Justin