2015 - 2017 Corvette with A8 Tranny
Service Bulletin:
Shake and/or Shudder During Light Throttle Acceleration Between 25 and 80 MPH at a Steady State
Last Updated: Thu, Mar 2, 2017 at 1:45 PM

Some customers may comment on any of the following conditions:

A shake and/or shudder during light throttle acceleration between 25 and 80 mph (40 and 128 km/h) steady state driving when transmission is not actively shifting gears.
A shudder feeling that may be described as driving over rumble strips or rough pavement.
For 2015-2016 vehicles, shudder feeling is evident in both Drive and M7 mode.
For 2017 vehicles, shudder feeling is evident in both Drive and L7 mode.
Diagnosis Instructions
To ensure TCC shudder is diagnosed correctly, please drive the following schedule on a smooth road with transmission sump temperature between 122°F (50°C) - 158°F (70°C ).

Important: For some road conditions, it may be required to apply the brake pedal and throttle simultaneously to stay within desired engine torque range, and engine/vehicle speed ranges.

Run the following tests for 3 operational modes:

A. Normal Operation (GDS2 for viewing only).

B. GDS2 Commanding TCC in Disabled Operation. (TCC Open).

C. GDS2 Commanding TCC in Enabled Operation. (TCC Locked).

To confirm TCC shudder, the vibration concern must be created in normal operation (Mode A) of the test.
If the concern is gone with the torque converter clutch disabled (Mode B, TCC Open) and is gone when the torque converter clutch enabled (Mode C, TCC Locked), the vibration root cause is TCC shudder and the fluid flush procedure corrective action described below should be performed.

If the concern is not present in Mode A, then the vibration concern is not TCC shudder.
If the concern is still present with the torque converter clutch disabled (Mode B) or with the torque converter clutch enabled (Mode C, TCC slip speed at zero), the root cause of vibration is NOT shudder.
Vibrations not identified as shudder should be further investigated using the “Vehicle Vibration Diagnosis in SI as a starting point.

The use of the PICO scope and NVH software can be used to confirm TCC shudder, Engine, Tire or Driveline component related conditions.

To confirm TCC shudder record the PICO scope data while driving in 8th gear in the application specific condition above. Minimize extraneous vibration input by testing on a smooth road and correct any other known vehicle vibration issues (tires, brakes, etc.) before conducting test.
If TCC Shudder is present, a vibration peak will appear (highlighted by arrow below) within +/-2 Hz of the frequency listed in the table above.
TCC Shudder vibration frequency should remain constant in 8th gear as indicated in the above table.
If the vibration frequency follows vehicle speed or engine speed, then it is NOT TCC Shudder.

Service Procedure

Important: Requires Mobil 1 Synthetic LV ATF DEXRON HP (GM Part No. 19353429, in Canada 19353430).

Note: U.S. dealers must order the Mobil 1 Synthetic LV ATF DEXRON HP fluid through your local General Motors oil distributor. Canadian dealer must order through CCA.

Step 1: Cooler Flush, Drain, Clean pan/magnet, Replace Filter (If needed), Oil Fill, & Circulate New Fluid

Note: The Transmission Fluid Cooler Flow Test and Flushing procedure can be located by building the vehicle in SI, select Transmission,
Transmission Cooling, Diagnostic Information and Procedures. Select the appropriate transmission.

1 a.) Flush the cooler lines and cooler, refer to SI for proper procedure.

Note: DEXRON VI transmission fluid may be used to flow and flush the transmission cooling system. Compressed air should be used to remove any residual fluid from transmission cooler lines.

1 b.) Remove the transmission fluid pan and drain transmission fluid following SI procedures for the application you’re working on. Discard all oil.

Note: If you find that the fluid is cloudy, milky, or appears to be contaminated with water or engine coolant,
DO NOT proceed with below steps.
Follow Both SI Procedures for “Cooling System Leak Testing (L83, L86)” and “Engine Coolant/Water in Transmission.”

1 c.) Clean the pan/magnet if any metallic particles present and replace transmission filter if debris is found.

1 d.) Install the transmission fluid pan and refill with new transmission fluid using enough volume to have oil come out of oil level check plug.

Important:
Operate the vehicle on the hoist for 10 minutes. Cycle through all forward gear ranges, Reverse and Neutral.

Step 2: Drain, Oil Fill, & Circulate New Fluid

2 a.) Remove the transmission fluid pan and drain transmission fluid again. Discard all oil.

2 b.) Install the transmission fluid pan and refill with new transmission fluid using enough volume to have oil come out of oil level check plug.

Important:
Operate the vehicle on the hoist for 10 minutes. Cycle through all forward gear ranges, Reverse and Neutral.

Step 3: Drain, Oil level Set, and Drive to Evaluate

3 a.) Remove the transmission fluid pan and drain transmission fluid again. Discard all oil.

3 b.) Install the transmission fluid pan and refill with new transmission fluid following the “Fluid Fill Procedure” in SI to obtain correct fluid level.

The shudder should be improved after the completion of this triple flush procedure.

Note:
Shudder should improve right away, but for full affect the vehicle may need to be driven up to 200 miles (322 km). and at least two cold to hot drive cycles before determining if the fluid flush corrected the condition or not.
Do not re-evaluate vehicle for additional customer shudder concerns until the vehicle has been driven 200 miles (322 km).

Warranty Information
For vehicles repaired under the Bumper-to-Bumper coverage (Canada Base Warranty coverage), use the following labor operation. Reference the Applicable Warranties section of Investigate Vehicle History (IVH) for coverage information.