January 21, 2013
In GM 4L60-E, 4L65-E and 4L70-E units, continuous oscillation of the Forward and Reverse abuse valves creates bore wear, allowing clutch feed pressure to exhaust. This reduced clutch pressure causes slippage and burn-up. The Sonnax drop-in replacement valve is slightly oversized and has extended spool lengths to provide additional sealing contact area. The stabilization flats on the inboard end of the spool maintain OE flow, but provide continual valve support while stroking. Annular grooves have been added to prevent side loading and a new spring is provided for the modified valve length. Sonnax Forward and Reverse abuse valve kit 77754-35K fits either the Forward or Reverse abuse location and includes a replacement bore plug.
Vacuum testing at the port(s) indicated fails to hold the recommended minimum in-Hg, or if wear is visually detected.