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


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


The Sonnax kit's dual seals stabilizes and completely seals the piston in the bore.

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

Pinless Forward Accumulator Piston Kit
Part No. 77987-01K

Dual Seal design

View Instructions

In GM 4L60-E, 4L65-E and 4L70-E units it is common for the plastic forward accumulator piston to wear or crack. This causes a loss of fluid, resulting in delayed engagement, slips, burnt clutches and/or bands. Repeated reciprocation of the accumulator piston causes the piston pin bore to wear, while fluid loss through the piston pin bore or cracks causes forward clutch to slip. Sonnax pinless forward accumulator piston kit 77987-01K eliminates these problems.

  • Dual seals stabilize and completely seal the bore, providing a tight seal even after thousands of cycles
  • Pinless design eliminates the possibility of pin leakage, and the additional length stabilizes the piston to prevent piston cocking
  • Includes steel balls for plugging existing pin bore in valve body
  • Piston
  • D-Ring
  • PTFE Seal
  • Steel balls (2)
  • Material: Aluminum

  • 77987 01k combo
  • 77987 01k