sonnax-black Facebook-color LinkedIn-color maillink printlink r_and_r_only SERVOFIX-logo-web Twitter-color VBFIX-logo-web video-logo-web warranty_only Youtube-color


  • Low line pressure
  • Low Reverse boost
  • Poor upshift in manual low
  • Delayed Reverse


Worn reverse boost valve sleeve or wear at pump body.


This large reverse boost valve assembly, made from hardened steel, restores reverse boost pressure control and prevents premature wear related failures.

200-4R, 4L60

Reverse Boost Valve Kit
Part No. K77898A

Large ratio, Factory style sleeve, no O-rings

View Instructions

Vehicles with a GM 4L60 (200-4R) transmission 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
  • K77898a combo
  • K77898a