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Brand: Sonnax

Other Part Number: S74507RBK

Type: Pump Boost valve kit

Interchange Part Number: S74507RCK

Items Included: Reverse Boost Valve and Sleeve Kit

Manufacturer Part Number: K77898A

Material: Steel

Universal Fitment: Yes

Vintage Part: No

Performance Part: Yes

200-4R, 4L60, 700R4 Transmission

Reverse Boost Valve Kit
Part No. K77898A

Large Ratio, Factory-Style Sleeve, No O-Rings

Vehicles with GM 200-4R and 4L60 transmissions often have complaints of poor Reverse boost or upshifts in manual low. This complaint is generally caused by a worn Reverse boost valve sleeve or wear at the pump body. To resolve these problems, Sonnax offers larger ratio (.283"), factory-style Reverse boost valve kit K77898A.

Due to the differences in the thermal expansion rate of steel and aluminum when the transmission approaches operating temperature, the sleeve has been allowed excessive clearance and scrubs the bore.

  • Sleeve and valve are made from hardened steel for increased wear resistance
  • Sleeve lands have been lengthened to add better sealing and stabilizing capabilities to prevent bore wear
  • The reverse boost valve spool lands have been lengthened to aid in maintaining hydraulic integrity
  • Valve
  • Sleeve

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