From Moped Wiki
"Coaster-brakes" or "pedal-back brakes" allow the rear brake to be engaged when the pedals are rotated backwards. Many bicycles have this ability, particularly BMX bikes.
- Most often found on Sachs mopeds and manual shift mopeds.
- On Sachs bikes with the 505 engine that allows for coaster-brakes, it makes the left-hand lever not engage the rear brake cable as usual but the decompression/clutch cable.
- On manual shift mopeds it allows for the left-hand lever to act as a clutch, and which also doubles as a twist-shift mechanism.