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Symptoms:
  • Delayed Reverse
  • Low line pressure
  • Poor modulator control
  • Soft shifts
Cause:

A worn boost valve or boost valve sleeve.

Correction:

Restore proper line pressure control with closely toleranced boost assemblies, made from wear-resistant materials.

4R44E, 4R55E, 5R44E, 5R55E

Boost Valve Kit

Part No.

37947-03K

Boost Valve Kit
  • 37947-03k_combo

  • Boost Valve Kit

Small_37947-03k_combo Small_37947-03k

4R44E, 4R55E, 5R44E, 5R55E

Boost Valve Kit

Part No. 37947-03K

  • Valve
  • Sleeve

Increased Ratio

Complaint:

  • Delayed Reverse
  • Low line pressure
  • Poor modulator control
  • Soft shifts

Cause:

A worn boost valve or boost valve sleeve.


Correction:

Restore proper line pressure control with closely toleranced boost assemblies, made from wear-resistant materials.

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)
LineReverseLineReverse
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

Related Parts

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Valve Body Layouts

Sonnax valve body layouts provide a detailed overview of individual units making it quick and easy to determine what’s available for the specific valve body you’re working on. See all Sonnax valve body layouts.

Valve Body Layout Ford 4R/5R44E, 4R/5R55E

Related Tech Articles

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