• Cracked pistons
  • Burnt clutches
  • Burnt bands
  • Forward slip
  • Delayed engagement
  • Aluminum pistons wear at the pin bore


Wear at the piston pin bore due to repeated reciprocation and/or cracks in the plastic accumulator piston.


The Sonnax aluminum piston is a direct replacement for the OE plastic piston and restores sealing integrity at the pin bore.

4L60-E, 4L65-E, 4L70-E

Forward Accumulator Piston
Part No. 74927-AP

OE Part No. 8686017 or 24200126

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In GM 4L60-E, 4L65-E and 4L70-E units, it is common for the plastic forward accumulator piston to wear or crack and older aluminum piston bores to wear from repeated reciprocation. This causes a loss of fluid, resulting in delayed engagement, slips, burnt clutches and/or bands. Sonnax aluminum forward accumulator piston 74927-AP eliminates the cracking problem and restores hydraulic integrity at the pin bore.

  • 74927 ap combo
  • 74927 ap