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 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
Harcoat 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
Drop-in Zip Valve™ parts install quickly and easily

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


Learn More About Zip Valve™ Drop-In Repairs

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