This bulletin applies to 2007-2012 Chevy Colorado 4WD vehicles equipped with 4L60E/4L65E/4L70E automatic transmissions. The concern may involve a hard or harsh 1-2 shift after transmission service.
When inspecting the 1-2 accumulator assembly while diagnosing this condition, it is important to note that all transmission models use an inner spring (104 in illustration), but many models do not use an outer spring (54 in illustration).
The 1-2 accumulator piston/spring assembly is transmission model-specific and may make use of only an inner spring or may use both an inner and outer spring. The most accurate and up-to-date source of information on how the accumulator assembly is built is available under Section Transmission/Transaxle /Automatic Transmission – 4L60-E/4L65-E/4L70-E – Specifications – 1-2 Accumulator Piston Spring Selection in the service manual.
Do not install an outer spring in a transmission built with only an inner spring. Adding the outer spring may cause additional harsh 1-2 shifts and/or delayed 2-1 downshifts.