Sonnax turbine stiffener plate GM-WS-39 is used to create a stronger turbine in GM TH400, Allison AT 540/545, BW 310mm LU (A618) and BW 310mm NLU converters. The design incorporates a contour and reduced outside diameter for optimum fit to the turbine.
The Sonnax plate can be welded as-is to the turbine in GM TH400 and BW 310mm NLU converters, but in Allison AT 540/545 and BW 310mm LU (A618) converters, GM-WS-39 must first be modified.
To weld GM-WS-39 to the turbine, a stock TH350 transmission forward clutch piston may be used as tooling to hold it in place for tacking and welding. Tack welding four to six segments on both the inside and outside diameters of the stiffener plate should be adequate, however some may elect to weld completely around both diameters for maximum strength.