radio static goes away when braking

If it's the CB then it's an issue of static electricity being built up, and discharged through the wheel/tire assembly when the brake shoes/pads make contact with the drums/rotors.

I've heard of putting graphite powder in the hub oil to make it more conductive, but I don't know if that actually works and I have no idea if that causes premature wear of the hubs and/or bearings.

 

graphite won’t hurt anything it just turns oil black.

There are two things you can do other than adding graphite to see what it could be, the first is if you are standing still you can try this one. Take a wire to ground the body and put in into the ground, if it stops then it is the static build up.

The other is to use old bungy cords and hang them off the steps or some other metal part, like the fuel tank or air tank. Let the bungy touch the ground and rub it. This will discharge the static, a lot of late sixties and early seventies cars had rubber straps added to the rear bumper to discharge static. My neighbors yenko Corvair has little springs in the grease caps to do the same thing.

 

The only thing I can think of is radio antennas on vehicles have a static filter. So that it’s not staticky when moving. So maybe the static filter isn’t working and when you hit the brakes the truck not moving as fast would mean less static.

Guess I’d try a new antenna.