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Servicing a harsh GM shift

A harsh 1-2 shift following transmission service may be experienced in GM vehicles equipped with the 4L60E, 4L65E or 4L70E transmissions.

Vehicle applications include 2007-2012 Chevy Avalanche, Colorado, Express and Silverado, 2007-2009 Chevy Suburban, Tahoe and Trailblazer, 2007-2012 GMC Canyon, Savana, Sierra and Sierra Denali, 2007-2009 GMC Envoy, Yukon, Yukon XL and Yukon XL Denali, 2007-2010 Hummer H3 and H3T, and 2007-2009 Saab 9-7X and 9-7X Aero.

The issue involves the 1-2 accumulator spring. When inspecting the 1-2 accumulator assembly while diagnosing a condition of “Harsh 1-2 Shift,” it is important to note that all transmission models use an inner spring (104), but many models do not use an outer spring (54).

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 SI.

NOTE: Do Not install an outer spring (54) in a transmission built with only an inner spring (104). Adding the outer spring may cause additional harsh 1-2 shifts and/or delayed 2-1 downshifts.

Some GM transmission 1-2 accumulator assemblies feature both an inner and outer spring, while others feature only an inner spring. Adding an outer spring to an accumulator that was designed with only an inner spring can cause harsh 1-2 shifts.
<p>Some GM transmission 1-2 accumulator assemblies feature both an inner and outer spring, while others feature only an inner spring. Adding an outer spring to an accumulator that was designed with only an inner spring can cause harsh 1-2 shifts.</p>

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