April 21, 2021
GM 8L45 and 8L90 transmissions may have TCC apply and release problems. Bore wear or a stuck converter feed limit valve can result in converter overheat, incorrect TCC apply or release, inadequate lube and cooling, and converter over-pressurization. Reaming the bore and installing the Sonnax oversized converter feed limit valve kit 154740-22K will restore proper valve function, resulting in proper TCC apply and release, regaining control of lube and cooling.
Inboard Location: Install Sonnax converter feed limit vacuum test tool 154740-TL22 with vacuum testing tube attached to long end (Figure 3). Vacuum should hold a minimum of 18 in-Hg (Figures 1 & 3).
Outboard Location: Insert either the OE valve or Sonnax converter feed limit vacuum test tool 154740-TL22 centered in the port (Figure 2). Vacuum at indicated port should hold a minimum of 15 in-Hg (Figures 1, 2 & 3).