Order a 5 gal pail of Evapo-Rust from Northern Tool online, and pick up at the store for no added shipping cost.

Inspect after 30 minute to see progress. Wash off Evapo-Rust before it dries with a 2" paint brush and mineral spirits and wipe with shop rag. Buff with an 8" wire wheel in a drill motor. I can't prove it, but I believe wire brushing slows or prevents rusting.

If all rust down to the bottoms of all rust pits isn't gone, re-immerse and repeat.

If all rust down to the bottoms of all rust pits is gone, wash and wipe with mineral spirits, wire wheel, followed by brushing on phosphoric acid with a 1" nylon paint brush. Wash off acid with mineral spirits before the acid dries. This leaves a very thin and almost invisible coat of acid that almost always prevents re-rusting. If minor re-rusting does occur later, it is easily and quickly removed by re-wetting with phosphoric acid and scrubbing with a Scotch-Brite pad. This works very well on steel body panels waiting for paint that should not be oiled. Wash the Scotch-brite pad immediately with water or it will turn to powder.

I've also used just vinegar and both Evapo-Rust and vinegar on cast iron brake drums with good results. A short dip in Evapo-Rust followed by a vinegar soak seemed to make the rust scale pop off and finish up de-rusting quicker. Use the same methods as above to prevent rust without oil, or you can add oil too if you want.