system in the event of locked brakes.
h. Chock Blocks.
be placed in back of, or in front of, the semitrailer Wheels as
parked on an
incline or when it is to be coupled or uncoupled.
blocks are made of triangular layers of wood (laminae) bolted
The chock blocks are chained to the chassis frame
beams to prevent loss and chains and blocks are carried in
brackets when not in use.
i. Types of Brakes.
The brakes are of the air-over-
hydraulic type. Two brake hydraulic master cylinders,
converting the energy of compressed air into hydraulic
ated semitrailer wheel brakes.
( 2 ) Semitrailers M270 and M269. The brakes are of the
air-actuated type. Air pressure is used to operate the
mechanical brake mechanisms at the semitrailer wheels,
applying the brakes with pressure in proportion to the