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4. Verify the range engagements are immediate and not harsh. 7. Monitor the transmission range on the scan tool engine list. 1. Apply the brake pedal and ensure the parking brake is set. 2. Move the shift selector through all ranges. 3. Pause 2 to 3 seconds in each range. 4. Return the shift selector to PARK. 5. Verify that all of the selector positions match the scan tool display. 8. Inspect the throttle angle input. 1. Apply the brake pedal and ensure the parking brake is set. 2. Ensure the shift selector is in PARK. 3. Monitor the throttle angle while increasing and decreasing the engine speed with the throttle pedal. The scan tool throttle angle should increase and decrease with the If any of the above checks do not perform properly, record the result for reference after the UPSHIFT CONTROL AND TORQUE CONVERTER CLUTCH (TCC) APPLY The transmission control module (TCM) calculates the upshift points based on the throttle angle Perform the following steps: 1. Choose a throttle position of 10 percent, 25 percent or 50 percent. All throttle angles shown should be tested to cover the normal driving range. 2. Monitor the following scan tool parameters: Throttle angle Vehicle speed Engine speed Turbine speed Output shaft speed Commanded range Slip speed
2008 Chevrolet Silverado 1500 2008 TRANSMISSION Automatic Transmission - Allison - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado
Solenoid states 3. Place the shift selector in DRIVE. 4. Using the chosen throttle angle, accelerate the vehicle. Hold the throttle steady. 5. As the transmission upshifts, note the vehicle speed when the shift occurs for each range change. There should be a noticeable shift feel or engine speed change within 1 to 2 seconds 6. Shift speeds may vary slightly due to transmission fluid temperature or hydraulic delays in responding to the electronic controls. Note any harsh, soft or delayed shifts or slipping. Note any noise or vibration. 7. Repeat steps 1-6 to complete all throttle angles. 8. Inspect for TCC apply in SECOND, THIRD, FOURTH, FIFTH and SIXTH range. Note the TCC apply point. When the TCC applies there should be a noticeable drop in Lightly tap and release the brake pedal. The TCC will release on most applications. PART THROTTLE DETENT DOWNSHIFT 1. Place the shift selector in DRIVE. 2. Accelerate the vehicle to a speed just above the FIFTH to SIXTH shift point, using less than 50 percent throttle. 3. Quickly increase throttle angle to greater than 63 percent. 4. Verify the following conditions: The TCC releases. The transmission downshifts immediately to FIFTH range. MANUAL DOWNSHIFTS 1. Place the shift selector in DRIVE. 2. Accelerate the vehicle to obtain SIXTH range. IMPORTANT: The TCC will not engage until the engine is in closed loop operation. The vehicle must be in a near cruise condition, not
2008 Chevrolet Silverado 1500 2008 TRANSMISSION Automatic Transmission - Allison - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado
3. Place the shift selector in RANGE SELECTION MODE (M). 4. By pressing the "+/-" button on the shift selector select the desired preselect range. 5. Release the throttle. 6. Verify the following conditions: The TCC releases. The transmission downshifts immediately to the preselected range. Downshifts will The engine slows the vehicle. MANUAL 2-1 DOWNSHIFT 1. Place the shift selector in DRIVE. 2. Accelerate the vehicle until the 1-2 shift occurs. 3. Go to 8 km/h (5 mph) above the 1-2 shift point. 4. Release the throttle while moving the shift selector to FIRST. 5. Verify the following conditions: The TCC releases. The transmission immediately downshifts to FIRST range. The engine slows the vehicle. COASTING DOWNSHIFTS 1. Place the shift selector in DRIVE. 2. Accelerate the vehicle to SIXTH range with the TCC applied. 3. Release the throttle and lightly apply the brakes. 4. Verify the following conditions: The TCC releases. Downshifts occur in normal sequence and the transmission returns to FIRST range MANUAL RANGE SELECTION The shift solenoids control the upshifts in the manual ranges. Perform the following tests, using 10-15 percent throttle angle. REVERSE
2008 Chevrolet Silverado 1500 2008 TRANSMISSION Automatic Transmission - Allison - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado
1. With the vehicle stopped, move the shift selector to REVERSE. 2. Slowly accelerate the vehicle. 3. Verify that there is no noticeable slip, noise or vibration. TORQUE CONVERTER DIAGNOSIS The torque converter clutch (TCC) is applied by fluid pressure, which is controlled through the TORQUE CONVERTER STATOR The torque converter stator assembly can have 2 different malfunctions. The stator assembly freewheels in both directions. The stator assembly remains locked up at all times. POOR ACCELERATION AT LOW SPEED If the stator is freewheeling at all times, the car tends to have poor acceleration from a standstill. If the engine freely accelerates to a high RPM in NEUTRAL, you can assume that the engine and POOR ACCELERATION AT HIGH SPEED If the stator is locked up at all times, performance is normal when accelerating from a standstill. You should be able to turn the race clockwise, but should have difficulty in moving the race WHINE NOISE IMPORTANT: Do not confuse this noise with pump whine noise, which is
2008 Chevrolet Silverado 1500 2008 TRANSMISSION Automatic Transmission - Allison - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado
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