The 7o class railcars were converted into Thumpers from loco hauled coaches and 550 was one such vehicle
Built as a buffet in 1950 on an older underframe dating from 1936 it ran as loco hauled Buffet 87 for many years.
It was wired so it could also be used used with multi purpose diesel and renumbered to 550 in 1959
In 1966 it was further modified to run with the 70 Class DEMU.
It has been restored to original condition by the Railway Preservation Society of Ireland and is displayed in their museum in Whitehead