In 1961 the Superba Special was changed to the ''Marathon''. An overhead valve, six-cylinder engine was made standard in the station wagon. In 1963, a new luxurious sedan was introduced as the Checker Town Custom Limousine. It was built on a 129-inch wheelbase and had all power equipment standard, including a partitioned driver compartment.

From 1964 through 1982 the Checker went through more dramatic changes. In 1964 Checker dropped the Superba name and all cars designate as A12's were called ''Marathons''. The different models were identified by a letter suffix to the A12. For example, the wagons were A12W's and the extended wheelbase limos were A12E's. The cabs became A11's with the extended version the A11E. The Continental engines were dropped also in 1964 for the Chevrolet 230 Six, and the 283 V8. In 1965 the Chevy 327 V8 was offered, and in 1968 the engines were the 230 in-line six, the 307 and 327 V8's.

In late 1969 the Medicar was introduced. It was an odd looking vehicle with it's roof raised ten inches and the rear doors opening to a full 180 degrees. It was built on a 129-inch wheelbase and could accommodate up to three wheelchairs with the right hand front bucket seat removed. Only 100 of these cars ever made it off the production line, and in late 1970 it was discontinued.