TM-9-2320-273-10

TRUCK, TRACTOR, LINE HAUL; LIGHT EQUIPMENT TRANSPORTER; TRUCK CHASSIS; MEDIUM EQUIPMENT TRANSPORTER

TECHNICAL MANUAL; OPERATOR’S MANUAL

DECEMBER 2012
TM-9-2320-273-10

  TM-9-2320-273-10 - Page 185 of 452

EFFICIENT AND ECONOMICAL DRIVING TECHNIQUES (M915 THROUGH M920) -
CONTINUED
Downhill Braking
WARNING
Failure to comply to downhill driving procedures may cause
loss of vehicle control and result in injury or death to
personnel. Seek medical attention in the event of an injury.
Excessive use of the service brake to control downhill speed
will result in loss of braking power due to heat build up.
Failure to comply may result in severe injury or death to
personnel. Seek medical attention in the event of an injury.
1. Follow proper downhill procedure by selecting a gear which allows the engine
with the engine retarder applied to control truck speed with engine rpm at or
below 2,000 rpm and service brakes not applied. When approaching a downgrade,
progressively select a gear when combined with the engine retarder allows driver
to maintain an engine speed of 1,750–2,000 rpm.
2. As engine speed exceeds 2,000 rpm, use one positive application of the service
brakes to slow the engine speed to 1,650 rpm, release engine retarder, downshift
one gear, and reapply engine retarder. Repeat procedure until engine speed can be
maintained between 1,750–2,000 rpm.
3. In the event engine over speeds (above 2,100 rpm), make one positive firm
application of the service brakes to slow vehicle speed.
4. In the event transmission over speeds (above 2,300 rpm) and total transmission
disengagement, perform the following:
a. Release engine retarder.
b. Upshift
c. Make one positive application of the service brakes to slow vehicle speed
and regain control of the vehicle.
5. If the transmission totally disengages from the engine due to a shift being made
with the engine retarder applied and engine speed has returned to low idle free
wheeling, accelerate the engine to engage transmission.
6. If experiencing a total loss of braking due to heat buildup:
a. Apply engine retarder (place switch in high mode).
b. Upshift as engine speed approaches 2,100 rpm. Prior to each upshift, release
engine retarder.
c. In 16th gear, continue to apply engine retarder and maintain directional
control of vehicle.
END OF TASK
TM 9-2320-273-10
0010
0010-19


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