Remove a rusted trailer hitch with penetrating fluid and an air chisel, not a sledgehammer. It's easier and won't bend or break anything.
Generously spray the opening to the hitch receiver with a penetrating fluid. Then insert the spray straw deep into the corners of the receiver and spray liberally.
Rap the sides, top and bottom of the hitch receiver for 15 seconds with blows from the air hammer. Spray again. Repeat the rapping until the ball mount loosens.
Air chisel and hammer bit
When the ball mount on your trailer hitch is rusted in place, don't whack at it with a sledgehammer. Here's what to do instead. Buy a can of CRC Freeze Off penetrating spray and an air chisel fitted with a “hammer bit.” The air chisel will run about $15 and the extra bit will be about $8. Spray the opening to the hitch receiver. This newest style of penetrating fluid chills the metal, causing it to contract to help break the rust seal. Then use an air chisel fitted with a hammer bit to knock everything loose. The air hammer will break up the rust, spread the penetrant and free up the ball mount. Once it's free, just tap the rusted ball mount out with a hammer. If you plan to reuse the rusty mount, coat it with a rust converter or waterproof marine grease.
Have the necessary tools for this DIY project lined up before you start—you’ll save time and frustration.
You'll also need an air chisel and hammer bit.
Avoid last-minute shopping trips by having all your materials ready ahead of time. Here's a list.