TM 9-2330-294-14
Figure 1-2. Semitrailer, low-bed, heavy-equipment transporter, 60-ton, M747 (right rear view ).
b. Electrical System. The semitrailer is equipped
provide normal suspension system operation, and it
with two composite taillights and 9 clearance marker
equalizes axle loadings. During normal operation,
lights. Each composite taillight is composed of a
the air suspension springs (4) exert downward
taillight, stoplight, turn light and marker light. In
pressure as required on the equalizer beam (5). This
addition. one utility outlet is provided at the fear of
provides a smooth, even ride for the axles (6). T
semitrailers No. 201 and on for use with towing
amount of air pressure exerted by the air suspensi
vehicles having floodlights or other auxiliary
springs can be adjusted to provide the varying
electrical equipment. Semitrailers no. 1 through 200
pressure required for different payload weights. The
are equipped with 3 utility outlets, one on each side
air suspension system control lever is located
by the clearance lights and one at the rear of the
midway on the left side of the semitrailer and has
vehicle. A military standard, 12-pin, intervehicular
three settings to permit pressure selection for light,
electrical receptacle located at the front of the
half or full loads, and a fourth pressure setting for
semitrailer provides an electrical power inlet from
lifting the rear axles. The rebound stop chain (2)
the towing vehicle. Two circuit breakers are located
limits the downward movement of the axle. The
a t the front of the gooseneck: one provides
shock absorber (3) performs a normal shock.
protection for the rightside taillights and clearance
absorbing function. When the axles are being raised,
marker lights and the other for the left side lights.
air pressure supplied to the axle lift (1) causes the lift
c. Suspension System. The two front axles utilize
assembly to expand upward. This expansion raises
an unsprung walking-beam suspension system. The
the axle lift rod (7) which in turn raises the equalizer
two rear axles use an air-suspension trailing-arm
arrangement. They may be raised approximately
schematic representation of the suspension air
three inches by a pneumatic lift system if the
system.
semitrailer is not loaded. This provides better
NOTE
maneuverability when turning corners, reduces tire
The four semitrailer axles are herein
wear when driving without a payload, and aids in
designated as number 5, 6, 7 and 8 in accord
changing wheels. The rear axles can also be raised
with the concept of the towing vehicle.
while the semitrailer is loaded with lighter weight
semitrailer as a road unit. However, number
of towing vehicle axles may vary.
two functions. It exerts a downward pressure to
1-2