Sonnax Pinless Accumulator Piston Kit for GM 4L60, 4L60E, 4L65E, 4L70E

If your GM truck or SUV has developed a harsh, banging 1-2 shift or a sloppy, slurring one, and the fluid and filter are already fresh, the accumulator piston is very likely the culprit. The factory 4L60E uses a plastic piston riding on a pin, and after years of the piston reciprocating on every shift, the pin bore wears out. Once that wear passes a certain point the piston leaks fluid past the bore, the pump cannot keep up with the loss, and shift quality goes to pieces. The piston can also cock sideways and gall the aluminum accumulator bore, which turns a cheap fix into an expensive one.

This is the Sonnax patented pinless kit that engineers around the whole problem. Instead of a pin, the piston is longer and rides on dual seals that stabilize it in the bore and seal it completely, so there is no pin bore to leak and nothing to let the piston cock over. The kit includes steel balls that you drive into the existing pin bore in the case or cover to plug it off for good. The result is a firm, consistent 1-2 or 3-4 shift and an accumulator that will not wear out the way the plastic original did.

It fits the GM 4L60, 4L60E, 4L65E and 4L70E families, the units behind small blocks in Silverados, Sierras, Tahoes, Suburbans, Blazers and the rest of the GM rear-drive lineup. Install is well within reach of anyone comfortable dropping a transmission pan: pull the pan, swap the piston in the accumulator housing, plug the pin bore with the supplied ball, torque the housing back down gently since it is aluminum, and refill. Sonnax part 77998-03K. Ships from the USA.