Hearing protection is required for personnel when performing any function
on the M870A3 when the prime mover is in use. Failure to do so could
result in injury to personnel.
The M870A3 Semitrailer should always have the wheels chocked, with or
without a load, during coupling or uncoupling to prime mover and when
parked. Failure to not chock the wheels may result in injury or death to
The M870A3 MHET, with its prime mover, will have different operational characteristics
based on gross weight, differences between loaded and unloaded weight and suspension
characteristics. Safe operating limits are affected by the interaction of the vehicle
characteristics, load, road surface, weather, driver skill, and vehicle speed.
Before operating the trailer, ensure that all the operating procedures contained in this manual
are fully understood.
Pre-Trip Inspection. Certain items should be inspected prior to each trip. Appropriate procedures
for services and PMCS (Chapter 2, Section II) will be completed prior to operating the MHET.
Permits. See paragraph 2-11a
if a permit
is required prior
General. When driving the prime mover and trailer, the overall length must be kept in mind,
both when passing other vehicles and when turning. Because the unit pivots at the fifth
wheel, backing is also affected.
Road Surfaces. Uneven terrain, steep grades, crowned roads, and unimproved road
surfaces can introduce forces that will make handling difficult. Even a vehicle that is
properly maintained and loaded can be hazardous when excessive speed and certain road
conditions are combined.
Grades. Operations on grades requires caution. Use the same gear in descending a long
grade as when ascending. Gear selection should be made before descending a grade to
minimize the chance of a missed shift. Avoid excessive use of brakes on long down grades in
order to maintain air pressure and prevent overheating of the brakes.
Side Slopes. This trailer is not designed to be operated on excessive (15%) side slopes.
The trailer can be safely operated, with or without payloads, on side slopes commonly
encountered on highways or unimproved roads.
Turning. When turning corners, allow extra room. The trailer wheels will follow a track that is
inside the radius of the prime mover wheels. For right turns, drive about halfway into the
intersection and then cut sharply to the right. The forces affecting the stability of a tractor
trailer combination are increased during turning. The smaller the radius, the greater the force
trying to pull the vehicle over. Therefore, the tighter the curve, the slower the speed must be in
order to avoid a rollover.