Vehicles with a GM 8L45 or 8L90 transmission may exhibit high line pressure that results in harsh shifts, loss of cooler and lube flow and overheating of the transmission and converter. These problems may be caused by continuous oscillation of the shuttle valve within the shuttle sleeve, creating excessive wear and a path for balance line pressure at the pressure regulator valve to exhaust. This prevents proper positioning of the pressure regulator valve and can keep it in the higher pressure position. When in this position, bypass of excess pressure is not allowed and converter/lube/cooler feed pressure is greatly reduced.
Sonnax drop-in shuttle valve kit 154740-09K has upgraded materials and minimal clearances to prevent wear and restore proper hydraulic control. The length of the critical shuttle valve diameter has also been lengthened to provide better sealing and durability of the assembly.
Vacuum testing at the port(s) indicated fails to hold the recommended minimum in-Hg, or if wear is visually detected.