Whichever he's talking about is true for both lock pin and the kingpin as well as anything else you're trying to drive out with a hammer.
Best results come when the part is well supported, set it on an anvil, or back it up with a sledge hammer, big hunk of steel... you get the idea.

Grigg

•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-