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Symptoms:

  • Harsh engine breaking in 1st
  • Harsh engine breaking in 2nd
  • Harsh engine breaking in 3rd
  • No engine braking in 1st
  • No engine braking in 2nd
  • No engine braking in 3rd
  • Clutch failure
  • 3-2-1 Bump

Cause:

Wear at the low pressure control valve allows 1-2-3 regulated braking fluid to exhaust.

Correction:

Install the Sonnax oversized valve and end plug kit into a refurbished bore to restore correct hydraulic clearances and prevent future wear.

5L40-E, 5L50-E

Oversized Low Pressure Control Valve Kit
Part No. 55211-17K


You need this if... View Instructions

The low pressure control valve applies in 1st, 2nd or 3rd gear coast conditions, when engine braking is needed. Depending on the gear and solenoid states, 1-2-3 regulated fluid pressure is routed through this valve to provide engine braking through a controlled apply of the low/reverse clutch, 2nd coast clutch or O.D. clutch. If the bore has excessive wear, this regulated oil pressure is open to exhaust, resulting in 3-2-1 bumps on coast downshifts, no engine braking, and/or clutch failure. The Sonnax low pressure control valve kit 55211-17K easily can be installed into are furbished bore, and incorporates design upgrades to prevent future wear concerns.

  • Hard-coat anodized aluminum valve prevents wear
  • Outboard spool is 74% longer than the OE design, adding stability and critical hydraulic sealing for the 1-2-3 regulated oil pressure
  • An annular groove has been added to the outboard spool to hydraulically center the valve in the bore and prevent wear
  • Includes oversized end plug
  • Valve
  • Plug

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

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  • 55211 17k combo
  • 55211 17k

You need this if...

A vacuum test at either port indicated fails to hold 18" of vacuum or higher, or if visual wear is detected at the inboard overlap valve bores.

  • 55211 17k test