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  • Low line rise
  • TCC slip
  • Gear ratio codes
  • High line pressure in Reverse
  • Flare shifts


The boost sleeve increases line pressure for shift quality, engagement and proper TCC apply. As the sleeve wears, torque signal oil will leak to exhaustand line pressure will not increase as commanded.


These Sonnax kits restore proper clearance with upgrade design and material to prevent EPC and reverse boost loss. Increased performance and OEM ratio kits are available.

5L40-E, 5L50-E

Boost Valve Kit
Part No. 55209-01K

With spacer, large ratio

You need this if... View Instructions

Vehicles with a 5L40-E transmission are prone to poor line rise or high reverse pressure problems causing poor shift quality and clutch failure due to leakage at the boost valve assembly. Sonnax offers two replacement boost assemblies: the 55209-01K with large ratio (higher line rise and firmer shifts) and the OE ratio 55209-04K for factory performance.

  • Boost valves are hard-coat anodized to eliminate wear on the inside diameter of the sleeves.
  • Boost sleeves are made from alloy aluminum specifically designed to resist wear.
  • Increased performance 55209-01K or OE ratio 55209-04K assemblies are available.
  • Kit salvages costly 5L40-E pumps.
  • Valve
  • Sleeve
  • Spacer
  • Dia.: 0.531"
  • Dia.: 0.432"

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 5L40-E, 5L50-E Valve Body Layout

Gm 5l40 e vbl thumb

November 24, 2015

GM 5L40-E, 5L50-E Vacuum Test Guide

Topics: Vacuum Test Guides Vacuum Testing Transmission GM 5L50-E Transmission 5L40-E Transmission

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  • 55209 01k combo
  • 55209 01k

You need this if...

A Wet Air Test shows leakage between the EPC and Reverse ports or a Vacuum test is less than 18".

  • 55209 01k 04k test