This page offers some helpful info about Early Hydramatic On Car service and band adjustment. In most cases it is better to use the prefered band adjust tools and proceedures. But, is is possible to provide on-car band adjustment with units that have external adjustment screws. Be sure to pass this info to others or cross-link to your classic car site.
From "Fatsco" On-Car Band Adjustment PDF Click Here
From "Auto Trans" On-Car Band Adjustment Click Here
From PontaicSafari.com Pontiac On Car Maintenance Click Here
From Old Car Manuals site Click Here