Complaints: Delayed engagements, slipping in forward gears, burnt clutches and/or bands, plastic pistons crack and are not durable, aluminum pistons wear at the pin bore Cause: Wear at the piston pin bore due to repeated reciprocation and/or cracks in the plastic accumulator piston. Correction: The Sonnax kit's dual seals stabilizes and completely seals the piston in the bore. 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.