The GM 4L60, 4L60-E, 4L65-E and 4L70-E input drum assembly is known to crack where the input shaft is pressed into it (where the overrun clutch rides).
Sonnax offers a hardened steel sleeve that reinforces the input drum to prevent this failure. OE overrun pistons must be machined when using Sonnax input drum reinforcement kit 77733-02K.

Sleeve made from hardened chromoly steel
Can be installed in early- and late-model units*
Sleeve design will not block clutch feed oil

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