As seen on TV! One of Spike's truck / muscle car shows:
1 bucket to hold your part
1 table spoon of sodium carbonate (washing soda, NOT baking soda) for every gallon of water
1 clean metal bar
1 battery charger capable of 2 amps constant
stick your part in the tub, hook up the negative terminal to the part
stick the metal bar in the tub away from the part to be cleaned, hook up the positive terminal to it
turn on the charger set at 2 amps and watch the rust wash away. make sure to do this outside or in well ventilated area cause it creates hydrogen which goes boom boom.
don't use on non ferrous parts as they will get messed up.