Symptoms:

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

Cause:

Worn reverse boost valve sleeve or wear at pump body.

Correction:

Sonnax large ratio, drop-in Reverse boost valve kit, 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

You need this if... View Instructions Find a Distributor

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
  • Drop-in Zip Valve™ parts install quickly and easily
  • Valve
  • Sleeve

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.

GM 200-4R Valve Body Layout

GM 200-4R Valve Body Layout
  • 200-4R, 4L60 Reverse Boost Valve Kit K77898A
  • 200-4R, 4L60 Reverse Boost Valve Kit K77898A

You need this if...

Vacuum testing at the port(s) indicated fails to hold the recommended minimum in-Hg, or if wear is visually detected.

200-4R, 4L60 Reverse Boost Valve Kit Vacuum Test Locations