Harsh Downshift and Upshift Conditions

A harsh 5-4 downshift and harsh 1-2 upshift may be felt on some 2017 Colorado and Canyon models equipped with the 8-speed 8L45 automatic transmission (RPO M5T). These shift conditions may be noticed after approximately 25,000 miles (40,000 km) and may only be present when the transmission temperature is above approximately 110°F (43°C). At lower operating temperatures, the transmission will have acceptable transmission shift quality.

The harsh downshift and upshift conditions may be caused by the 2-3-4-6-8 return spring, which may have degraded over time. If these conditions are found, replace the 2-3-4-6-8 piston (Fig. 8, #526) and the 2-3-4-6-8 return spring. (Fig. 8, #527)


Fig. 8


In addition to replacing the return spring and piston, reseal the 2-3-4-6-8 and 4-5-6-7-8 reverse clutch assembly. (Fig. 9, #60)


Fig. 9


Refer to 2-3-4-6-8 and 4-5-6-7-8 Reverse Clutch Assembly Removal and 2-3-4-6-8 and 4-5-6-7-8 Reverse Clutch Disassemble and Assemble procedures in the appropriate Service Information. Use all special tools as needed and replace the single use fasteners and components during the repair.

TIP: When assembling the reverse clutch assembly, position the 2-3-4-6-8 clutch piston return spring, the 4-5-6-7-8 reverse clutch piston stop, and the 4-5-6-7-8 reverse clutch piston return spring in the orientation as observed during removal. Also, it will be helpful to loosely install the 2-3-4-6-8 clutch piston dam retaining ring and the 4-5-6-7-8 reverse clutch piston dam retaining ring before installing the tool. (Fig. 10)


Fig. 10


Be sure to follow the retaining ring measurement service procedure to determine each correct clutch backing plate retaining ring.

Refer to Bulletin #21-NA-076 for additional information and part numbers.


– Thanks to Mark Gordon


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