Some Jatco CVTs (continuously variable-ratio automatic transmissions) (RPOs M4M, MR8) available in the 2014-2019 Spark (Fig. 11) may have a short duration shudder on launch from a stop or on acceleration from a low speed, such as when turning a corner. The shudder is a momentary condition and may only occur under certain rates of braking and accelerating.

Fig. 11

Degradation of the CVT transmission fluid may alter the friction characteristics of the transmission and lead to shudder concerns during a shift from high or low range.

TIP: It’s normal for the transmission to remain in high range under medium to hard braking and may only make the high/low range shift on acceleration after the braking maneuver.

Drain and replace the fluid to reduce the shudder condition. Start the procedure by first removing the fluid pan and inspecting the magnets for metal debris. An abnormal amount of debris will be noticeable. (Fig. 12) It is normal to have some metallic build-up on the magnets. (Fig. 13) If the magnets show only normal magnetic sludge, reinstall the pan using a new gasket, if needed. Do not replace the transmission if metal chips cannot be felt in the magnetic sludge. Refer to #PIP5548 for additional information.

Fig. 12

Fig. 13

Reinstall the fluid pan and fill the transmission with five quarts (4.73 L) of ACDelco CVT fluid (P/N 19260800, U.S.; 19299096, Canada). Filled with five quarts, the transmission will be over full.

Disconnect only the transmission cooler return line from the transmission and route it into a suitable container. The cooler return line connects at the lower port at the transmission. (Fig. 14)

Fig. 14

Run the engine for 30 seconds and then check the amount of fluid in the container. The flow rate should be approximately one quart per 10 seconds. It will take 3–4 quarts (2.8–3.8 L) to flush the torque converter and discharge clean fluid from the return line. If necessary, run the engine again, but for no more than 20 seconds.

Reinstall the cooler return line and add two quarts of CVT fluid to the transmission. Adjust the fluid level following the instructions in the appropriate Service Information.

After replacing the fluid, the shudder should be noticeably improved within 100 miles (160 km). However, it may take up to 300 miles (480 km) for the new fluid to fully saturate the clutch plates.

– Thanks to Frank Jakubiec and Brady Jezewski