• Low line pressure
  • Delayed Reverse
  • No Reverse
  • Soft shifts
  • High line pressure
  • Harsh shifts


A worn boost valve sleeve allows torque signal and/or reverse pressure to cross leak or exhaust.


Sonnax drop-in boost valve kit restores hydraulic integrity to the circuits and properly controls line rise.

4T40-E, 4T45-E

Boost Valve Kit
Part No. 33886-03K

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

In GM 4T40-E and 4T45-E units, the boost valve assembly is activated by torque signal pressure from the pressure control solenoid and reverse pressure to aid in adjusting line pressure at the pressure regulator valve. This boost valve is continuously oscillating in the sleeve, which leads to wear and hydraulic leakage. When wear occurs, critical oil pressure is allowed to cross leak between the circuits or leak to exhaust. These leaks can result in either no line rise or an unwanted increase in line pressure. Sonnax boost valve kit 33886-03K that the hydraulic integrity and controls line rise.

  • Replacement boost sleeve delivers oil 360° around the valve, reducing side load
  • Sleeve is manufactured from highly wear-resistant aluminum
  • Hardcoat anodized aluminum valve combats premature wear
  • Tight tolerances on the sleeve and valve maintain an ideal fit that prevents leakage
  • Drop-in Zip Valve parts install quickly and easily
Learn More About Zip Valve™ Drop-In Repairs
  • Boost Valve
  • Sleeve
  • 4T40-E, 4T45-E Boost Valve Kit 33886-03K
  • 4T40-E, 4T45-E Boost Valve Kit 33886-03K

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.

4T40-E, 4T45-E Boost Valve Kit Vacuum Test Locations