7.13
FINAL DRIVE
7
ADC Operation
Engaging Front Gearcase: Active Descent Control (ADC) is
controlled by the ECU and will not enable until the following
conditions are met:
• Vehicle speed is below 15 Mph (24Kph)
• Throttle Position Sensor (TPS) is at idle position
• The AWD switch is switched to ‘AWD/ADC’
Once the conditions are met for engagement, ADC remains
engaged as long as the conditions are met.
With the AWD switch set to ‘2x4’, the vehicle drives only the
rear wheels (2 wheel drive). When the AWD switch is set to
‘4x4’ the magnetic coils are active, the AWD coil indexes the
clutch mechanism so that both front axles will engage when
there is a loss of rear wheel traction. In addition to the rear wheel
engine braking, the ADC coil provides front wheel engine
braking at speeds less than 15 Mph (24Kph) with the TPS at idle
position.
ADC Engagement: When the AWD switch is set to ‘4x4/
ADC’, a 12 Vdc current is present at the input shaft coil (1).
Operation is controlled by the ECU grounding and ungrounding
the coil. The coil’s magnetic field attracts a splined armature
plate (2) on the pinion (input) shaft (4). The energized splined
armature plate attracts the unsplined eccentric cam (3), which
begins to turn with the input shaft. The eccentric cam drives a
hydraulic piston/pump assembly (5). The pressure created by
the pump assembly forces hydraulic fluid through passages to
the piston assemblies (6) located in each case half. Hydraulic
pressure forces the piston assemblies inward to compress the
splined clutch packs (7) forming a dynamic coupling to each
front drive axle, resulting in true all-wheel EBS operation upon
deceleration.
Disengagement: Current to the ADC coil is turned off by the
ECU anytime the following conditions are met:
• Throttle Position Sensor (TPS) moves off idle position
• The AWD switch is switched to ‘4x4’ or ‘2x4’
• Vehicle speed is above 15 Mph (24Kph)
Hydraulic pressure stops and the pistons release, disengaging
the ADC function. The vehicle returns to rear wheel drive until
the next deceleration.
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