Some typical problems in 4R44E, 4R55E, 5R44E and 5R55E units are soft shifts, delayed reverse, poor modulator control and/or low line pressure in reverse. A worn boost valve is often the cause, allowing reverse and/or TV pressure to cross leak or exhaust. Sonnax offers two replacement boost valve kits for these units: the OE ratio kit 37947-01K and the increased ratio kit 37947-03K. The 37947-01K has OE spool ratios, to return line rise to stock condition. The 37947-03K assembly has increased ratios for slightly higher line pressures. Sleeves are manufactured from highly wear-resistant aluminum alloy. Valves are made from hard-anodized aluminum for better wear resistance. Tight tolerances restore the hydraulic integrity of the assembly. Kits improve engagement related to loss of boost oil and increased line rise in forward and reverse. Pressure Comparison Between OE and Increased Ratio Boost Valves EPC PSI 37947-01K (OE Ratio) 37947-03K (Increased Ratio) Line Reverse Line Reverse 30 107 135 114 143 75 178 224 194 243 120 250 313 275 343 Note: OE sleeves may come in either a 3- or 2-circuit design. Boost valve kits 37947-01K and 37947-03K may be used to replace either version Contents Valve Sleeve