• Delayed Reverse
  • Erratic Reverse pressure
  • Delayed Drive
  • Soft upshifts
  • Harsh upshifts


The valve within the sleeve separates Reverse boost oil from throttle signal (SLT) oil. Pressure in Reverse can either be delayed or added to SLT, which results in very high Reverse pressure. If the sleeve is worn and selector is not in Reverse, SLT is allowed to vent at the manual valve, reducing line rise, which affects engagements and shift quality.


The tightly toleranced, drop-in Sonnax boost valve kit restores proper hydraulic clearances and uses upgraded materials to prevent wear.

55-50SN, 55-51SN

Boost Valve Kit
Part No. 59947-07K

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

Vehicles with Aisin Warner 55-50SN or 55-51SN, GM AF23/33, or Jatco/Nissan RE5F22A transmissions may exhibit insufficient line rise in Reverse, delayed or slipping Reverse, and/or a burnt Reverse clutch. Continuous oscillation of the OE boost valve within the boost sleeve causes premature wear, creating a path for reverse apply boost pressure to exhaust and causing these concerns. Excess clearance/wear at the sleeve to bore interface can allow throttle signal (SLT) pressure to exhaust resulting in various shfit complaints. Installing Sonnax boost valve kit 59947-07K eliminates pressure loss, restoring proper line rise and robust Reverse action.

  • Sleeve is manufactured from highly wear-resistant billet aluminum
  • Valve is made of hardcoat anodized aluminum to prevent wear
  • Drop-in Zip Valve parts install quickly and easily

Also fits AF 23/33 and RE5F22A units. The 59947-07K should not be used with Sonnax oversized pressure regulator and boost valve kit 59947-12K.

  • 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.

Aisin AW 55-50SN, 55-51SN Valve Body Layout

Aisin AW 55-50SN, 55-51SN Valve Body Layout
  • 55-50SN, 55-51SN Boost Valve Kit 59947-07K
  • 55-50SN, 55-51SN Boost Valve Kit 59947-07K

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.

55-50SN, 55-51SN Boost Valve Kit Vacuum Test Locations