The BFH on kingpins can actually result in a bent axle. Support it solidly as close to the king pin as possible and give it a whack or three. If no movement you'll be better off pressings them out either in place if you can or remove the axle and take it to the press.

Whaling away with the big hammer for some time is not a good idea.

•1951 GMC 250 in the Project Journals
•1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
•1952 Chevrolet 3800 pickup
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"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-