Some typical problems in Ford 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 boost valve kit 37947-01K and the increased ratio boost valve 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
• Hardcoat anodized aluminum valve combats premature wear
• 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