Grove Published 3-23-2020, Control # 654-04 4-21
GRT655/655L OPERATOR MANUAL OPERATING PROCEDURES
Differential Lock Operation (Optional)
NOTE: Differential lock will not operate unless Drive
Selector Switch is in four-wheel drive position.
General
The purpose of the differential lock is to provide maximum
traction and control on poor road or highway surfaces. When
differential locks are actuated, the clutch collar completely
locks the differential case, gearing, and axle shafts together,
maximizing traction to both wheels of each axle. The lock
position will also protect against spinout.
When normal driving conditions exist (during periods of good
traction), differential locks should not be actuated. Axles
should be allowed to operate with differential action between
both wheels.
Obey the following precautions when engaging/disengaging
the differential lock function.
1. Lock/unlock differentials only when vehicle is standing
still or moving at a constant low speed with wheels not
slipping.
2. When traveling with differentials locked, do not deviate
from a straight path more than absolutely necessary.
3. Locked differentials cause crane’s turning radius to
increase, creating an understeer condition. Use caution,
good judgment, and drive at low speeds when operating
vehicle with locked differentials.
4. Lock differentials only when maximum traction is
needed on poor road or highway surfaces.
5. Always unlock differentials when need for maximum
traction has passed or when traveling on good road or
highway surfaces.
Operation
The differential lock function should preferably be engaged
when crane is stationary but may be engaged when moving,
if the following conditions are met:
• Crane is moving very slowly (creep speed).
• Wheels are not slipping at time of engagement.
Engage differential locks by doing the following:
1. Press and hold the Axle Differential Lock Control Switch
in the locked position with crane stationary or moving at
a slow speed.
If moving at a slow speed, let up momentarily on the
Foot Throttle Pedal to relieve torque on the differential
gearing. This will fully engage differential locks.
NOTE: When differentials are locked, the Axle Differential
Locked Indicator (20, Figure 4-18 and Figure 4-19)
is on.
2. Proceed over poor road condition cautiously.
When adverse condition has passed, disengage differential
locks by doing the following:
1. Release the Axle Differential Lock Control Switch,
allowing it to return to the unlocked position while
maintaining a slow speed.
2. Let up momentarily on the Foot Throttle Pedal to relieve
torque on the differential gearing, allowing differential to
fully unlock.
NOTE: When differentials are unlocked, Axle Differential
Locked Indicator will go off.
3. Resume driving at a normal speed using good driving
judgment.
CAUTION
Unexpected Operation!
When using differential lock, steering characteristics may
be affected.
Try to use four-wheel drive to gain adequate traction
before using differential lock.
Do not operate differential lock when traveling downhill; at
speeds above 16.1 km/h (10 mph); on hard, dry surfaces;
and/or during axle spin-out.
CAUTION
Possible Machine Damage!
When driving on hard, dry surfaces with differentials
locked, do not turn the wheels. Damage to drive line
components can result.
Do not lock differentials when wheels are slipping.
Damage to differentials can result.
CAUTION
Possible Loss of Vehicle Stability!
Do not lock differentials when vehicle is traveling down
steep grades and traction is minimal.
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