Product Details

High performance .283 inch low-reverse boost valve and sleeve, with O-rings for the GM 200-4R and 700R4 automatic transmissions.

• Part Brand: Sonnax
• Part number: K77898
• Transmission models: 700R4 and 200-4R
• Transmission makes: Buick, Chevrolet, GMC, Oldsmobile, Pontiac
• Boost Valve Diameter: .283 inch.
• O-ring style: Yes
• Year Range: 1980-1993
• Installation: Installs with transmission in the vehicle.

The larger ratio Oring style low-reverse boost valve for the GM 200-4R and 4L60 transmissions will help to fix the common complaint of poor reverse boost and upshifts in manual low. These complaints are generally caused by a worn Reverse boost valve sleeve or wear at the pump body. To resolve these problems, Sonnax offers this larger ratio (.283"), factory-style low 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.

Benefits of this boost valve with O-rings.

• The boost valve sleeve O-rings seal the Reverse boost circuit and prevent leakage from the pump body bore.
• The boost valve and sleeve are made from hardened steel for increased wear resistance.
• The boost valve 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.

This heavy-duty o-ringed style 700-R4 and 200-4R low-reverse boost valve will work in the following makes and model vehicles:

Buick

• Roadmaster, 1992-1993

Chevrolet

• Astro Van, 1985-1992
• Blazer, 1982-1992
• Camaro, 1982-1993
• Caprice, 1982-1993
• Corvette, 1982-1993
• S10, 1982-1992
• Silverado Truck, 1982-1992
• Suburban, 1982-1992
• Van, 1983-1993

GMC

• Canyon, 2004-2012
• Colorado, 1994-2012
• Envoy - XUV – Denali, 2001-2010
• K1500, Some K2500, 1982-1992
• Safari Van, 1985-1992
• Sierra Truck, 1982-1992
• Syclone 1991-1993
• Typhoon 1991-1993
• Van, 1983-1992

Oldsmobile

• Bravada, 1991-1992
• Custom Cruiser Wagon, 1982-1992

Pontiac

• Firebird & Trans Am, 1983-2002

These transmissions are part of the Turbo-Hydramatic series and are also known as: 700R4, 4L60, 700-R4, TH700-R4, MD8, THM700R4, THM700-R4.

This HP low reverse boost valve and sleeve works in all models and years of this transmission, including: 1982, 1983, 1984, 1985, 1986, 1987, 1988, 1989, 1990, 1991, 1992, and 1993.