The original 1908-09 'SL'  a.c. Driving Motor Brake Third (DMBT) coaches were adapted in 1929 to form eight two-car motor units for the South London line (2 SL)

Eight cars were converted to d.c. DMBTs.  The existing driving cab, guards compartment and one Third-class seating bay were replaced by an SR-standard 'front end' with space for the standard MV control gear at the rear of the cab.  The flat roof at the driving end that had originally carried the bow collector for the a.c. overhead power supply was, however, retained.  The converted cars seated 58 in seven third-class bays connected by a side aisle.

The other eight former DMBTs became Driving Trailer Brake Composites (DTBC).  They gained SR-standard cab fronts but retained the original part-width driving compartments and guards brake van area as well as the flat roof.  The two former Third-class bays at the inner ends were converted to two full-width First-class compartments seating 16 but the original side-aisle was retained for the remaining five Third-class bays, which seated 50.

The cars retained their original 60ft slotted plate-girder underframes, but the original pressed-steel bogies were replaced by other ex-LBSCR trailing bogies and new standard Central Section motor bogies with MV339 motors.  Standard side buffers and screw couplings were retained throughout.

Originally numbered 1901-1908, the units were renumbered 1801-1808 in 1934 as part of a general rationalisation of SR unit numbering.

In service

With standard power, control and braking systems, these converted units were capable of working in multiple with the rest of the SR's suburban-type fleet.  However, the width of the cars effectively limited them to the South London and Wimbledon-West Croydon lines together with associated routes to and from depots.  The units were paired at peak times on the South London line but otherwise usually worked singly.  The 2 SL and 2-Wim units carried unique headcode stencils with the number '2' on a full width plate, as with letter codes. In practice the headcode stencils were rarely removed, even remaining in situ when the units worked empty between Peckham Rye and Selhurst, usually via Tulse Hill and Norbury.

1807 was destroyed in 1940 at Peckham Rye depot.

In common with the rest of the suburban fleet, the First-class compartments in the DMBCs were reclassified Third-class in 1941, a change that later became permanent.

Unit 1802 was withdrawn in May 1951 and the remaining units in September and October 1954 as replacement new-build BR Standard 2EPB units were delivered.