M977 Through M985 General Operating Procedures (Cont)
2-11. DRIVE VEHICLE (CONT).
f. Use Engine Brake.
Apply engine brake only when vehicle tires have good
traction. Use of engine brake on slick surfaces can
cause vehicle to skid and cause personal injury.
Wheel brakes must be used in addition to engine brakes
for maximum use of brakes.
Set JACOBSR ENGINE BRAKE HIGH/LOW switch (1) to LOW.
Set JACOBSR ENGINE BRAKE ON/OFF switch (2) to ON.
JACOBSR ENGINE BRAKE INDICATOR LIGHT (4) will come on.
Lift foot off throttle treadle (3). Engine brake will automatically slow
Do step (4) for Non-FHTV model vehicles only.
If too much braking occurs, push in button (5) and set transmission
range selector (6) to a higher range.
If more braking is required, set JACOBSR ENGINE BRAKE
HIGH/LOW switch (1) to HIGH.
Engine brake operates best when engine speed is
between 1650 and 2100 rpm. Transmission torque
converter lockup may disengage below 1650 rpm
resulting in loss of engine brake.
Check that tachometer (7) reads between 1650 and 2100 rpm
whenever engine brake is used.