• Flare shifts
  • Long shifts
  • Delayed shifts


Wear of the exhaust backfill casting bore, and lack of full OE valve bore engagement can allow clutch backfill pressure to exhaust, resulting in slower clutch apply.


Sonnax drop-in exhaust backfill valve kit restores hydraulic integrity and has been redesigned with a longer spool for better engagement in both the inboard and outboard ports to better seal the backfill circuit.


Exhaust Backfill Valve Kit
Part No. 37000-17K

Fits '00–'15 units.

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

Trucks equipped with Allison® 1000/2000/2400 transmissions can be subject to delayed, long or flare shifts. This can be caused by bore wear or minimal OE valve bore engagement at the exhaust backfill valve. If there is excess bore wear or lack of full valve-to-bore engagement, the exhaust backfill circuit can leak all residual pressure and result in the noted drivability complaints.

Sonnax exhaust backfill valve kit 37000-17K nearly doubles the amount of critical valve spool-to-bore engagement, both at the inboard and outboard areas of the bore, resulting in better sealing of the exhaust backfill circuit.

  • Lengthened critical spool operate in non-worn portion of bore for added stability and wear prevention
  • Annular grooves help center valve in bore to reduce future side-load wear
  • Hardcoat anodized aluminum valve combats premature wear
  • Drop-in Zip Valve parts install quickly and easily
Learn More About Zip Valve™ Drop-In Repairs
  • Valve
  • Spring

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 Allison® 1000/2000/2400 Valve Body Layout

GM Allison® 1000/2000/2400 Valve Body Layout
  • 1000/2000/2400 Exhaust Backfill Valve Kit 37000-17K
  • 1000/2000/2400 Exhaust Backfill Valve Kit 37000-17K

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.

1000/2000/2400 Exhaust Backfill Valve Kit Vacuum Test Locations