• Low line rise
  • 1-2 Soft
  • 2-3 Soft
  • Delayed Reverse
  • Reverse shudder


Wear of the sleeve I.D. due to continuous oscillation of the boost valve.


Factory-style Sonnax drop-in boost valve kit restores hydraulic integrity with closely toleranced parts.


Boost Valve Kit
Part No. 34910-05K

Factory Style, No O-Rings

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Vehicles with a GM TH400 transmission frequently have poor line rise, soft 1-2 and/or 2-3 shifts,and/or Reverse engagement difficulties. These problems can be caused by the reciprocating boost valve wearing the inside diameter of the boost sleeve. When this occurs, oil that enters the modulated throttle valve orifice leaks past the boost valve and exhausts through the Reverse orifice or to the sump, resulting in poor line rise. Also, Reverse oil can exhaust both to the sump and back through the modulated TV orifice. The Sonnax boost vlave kit 34910-05K eliminates the above problems.

  • Boost valve and sleeve are manufactured from high-quality steel
  • Uses the same valve spool diameters as OE to regain factory shifts
  • Drop-in Zip Valve parts install quickly and easily
Learn More About Zip Valve™ Drop-In Repairs
  • Valve
  • Sleeve
  • TH400 Boost Valve Kit 34910-05K
  • TH400 Boost Valve Kit 34910-05K