Brake Mystery

[WhiteRhino]

Have bleed the brakes (correctly) several times, have replaced the master cylinder, have new front calipers. Have checked the rear drums for leaks......... After about 20 times the brake petal goes all the way to the floor........ After a couple of pumps it's fine again for about 20 more times ........ what's up ? I'm out of clues !

[DWitcher]

Have you checked the adjustment at the rear shoes?