Review on Efficient Axle Shaft Seal Installer for Ford 1998-2004 F-250/350/450/550 – OTC 6695 by Dan Reggae

You will need this tool when installing front axle seals. If you don't you will most likely damage the seal and your vacuum locked hubs will not work with the switch in the cab as the hubs will leak and not hold the vacuum. This tool is expensive but essential if you want your vacuum lockers to work after changing the axle seals.