April 21, 2021
Vehicles with a GM 8L45 or 8L90 transmission may exhibit high or low line pressure that results in harsh shifts, burnt clutches, loss of cooler and lube flow and overheating of the transmission and converter. These problems may be caused by wear of the pressure regulator bore casting at the VFS signal port area and/or at the shuttle valve sleeve. Wear at the inboard port of the pressure regulator bore allows VFS (throttle) signal pressure to leak, preventing proper action of the pressure regulator valve and potentially allowing it to remain in the low line pressure position. Wear of the shuttle sleeve due to continuous oscillation of the shuttle valve creates a path for balance line pressure at the pressure regulator valve to exhaust, resulting in excessive low line pressure.
Sonnax pressure regulator and O-ringed shuttle valve kit 154740-29K restores hydraulic integrity to the lineup by addressing wear that subjects the transmission to either excessive high or low line pressure with upgraded materials, O-ringed sleeve, and unique designs. The pressure regulator valve has been designed with a lengthened spring pocket spool at the VFS signal port area, which provides over double the sealing capability to this critical end of the valve and allows it to operate in unworn portions of the bore. The length of the critical shuttle valve diameter has been significantly 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.