PS Magazine - TB 43-PS-579
PS, The Preventative Maintenance Monthly
ISSUE 579
FEBRUARY 2001
Table 1-9
PS 579
FEB 01
3
PS 579
FEB 01
2
Drivers need to eyeball Tables 1-9 and 1-10 in TM 9-2320-280-10 for transmission
and transfer case range selections that will prevent wind-up.
CAUTION:
Damage to drivetrain will occur if transfer case ranges are not selected
properly. Refer to paragraph 2-11, Placing Vehicle in Motion, and paragraph
2-29, Operating on Unusual Terrain, for specific instructions.
Transfer Case Range Selection
Recommended Shift
Lever Position
Operating Condition
“H” (high range)
This drive range shall be selected whenever possible.
High range should be used when operating on all primary,
secondary, and off-road surfaces, where little or no wheel
slippage exists. This range is also to be used when encoun-
tering sharp, continuous turns on high traction surfaces.
This drive range shall be selected only when continuous
wheel slippage is evident; i.e., when operating in mud,
snow, loose sand, or on ice, and increased control or
This drive range shall be selected only when high ranges
do not provide sufficient power to negotiate steep hills or
downgrades. This range shall also be used when the vehicle
is mired and cannot be extracted using the high lock range.
Vehicle is disabled and must be towed.
HMMWV…
Note that Para 2-29, Operating on
Unusual Terrain, carries this info on
“If it is difficult to shift out of a
locked range, drivetrain torque buildup
may have occurred. If necessary to
relieve drivetrain torque buildup when
leaving a low traction surface for a
high traction surface, the vehicle
should be backed up for a distance of
approximately 5 feet before proceeding.”
Five feet may not be enough, and, in
some cases, backing up won’t solve the
problem at all. It’s best to operate right
the first time.
Dear Editor,
While we were servicing a HMMWV, we noticed a
grinding noise from the rear end when the truck
was turned.
Troubleshooting the source of the noise, we
found out the last driver had operated the truck
off-road with the transfer in low (L) range. He
then had driven back to the unit with the trans-
fer in high-lock (H/L) range, not high (H) range as
is required.
The TM says not to operate the truck on hard
surfaces with the transfer in H/L range, because
the wheels can’t slip as designed, so we thought
the differential had been damaged.
But before we began repairs one of our
mechanics mentioned that driving the HMMWV
backward for a short distance would “unwind”
the differential and stop the noise.
So we drove the HMMWV backward and, sure
enough, the noise went away. Maybe this will help
others who have this problem.
John Brown
AMSA 153
Nashville, TN
Use H range
when driving on
hard surfaces
From the desk
of the
Editor
579. 02- 03 (C)
1/10/01
3:32 PM
Page 1
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