Operation CHARM
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GMC Truck
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1990
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C 2500 Truck 2WD V8-305 5.0L
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Repair and Diagnosis
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Transmission and Drivetrain
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Automatic Transmission/Transaxle
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Description and Operation
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3L80/3L80HD (400/475) Automatic Transmission
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Hydraulic System, Brakes
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Functions of Valves & Hydraulic Control Units
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1-2 Detent Valve
1-2 Detent Valve
Senses regulated modulator pressure tending to hold 1-2 shift valve downshifted and provides an area for detent pressure for detent 2-1 shifts.