The caps are not holding the king pin in place, they are grease retainers/debris guards. Drill a hole in the cap and thread a sheet metal screw in and use it as a leverage. It would also help to know what vehicle being you are cussing at.
1957 Chevrolet 5700 LCF 283 SM420 2 speed rear, 1955 IH 300U T/A, 1978 Corvette 350 auto, 1978 Yamaha DT175, 1999 Harley Davidson Softail Fat Boy
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