Master cylinder piston preload?

[flatheadkid]

I just replaced the master cylinder on my 81 caddy. The new master cylinder matches the old one. Noticed that when I put the new master cylinder on the brake booster push rod the piston compressed a good 1/2". I adjusted the push rod all the way in and it still pushes the piston in about 1/4". I couldn't feel and preload in the old master cylinder but it is toast and easy to compress. Should there be preload on the piston. I'm thinking not. Any help would be greatly appreciated. Thanks for everyones time.
E.