In Kerberos 4, a salt was never used. The password was the only input to the one-way hash function. This has a serious disadvantage; if a user happens to use the same password in two Kerberos realms, a key compromise in one realm would result in a key compromise in the other realm.
In Kerberos 5 the complete principal name (including the realm) is used as the salt. This means that the same password will not result in the same encryption key in different realms or with two different principals in the same realm.