• Code 628, 1744, 1740
  • Reduced converter clutch life
  • Planetary failure
  • Bushing failure
  • Loss of lube oil


Casting bore wear at the bypass clutch valve and plunger sleeve wear allow converter apply and release pressure to exhaust.


The Sonnax reamer restores the bypass clutch control bore while the OS valve re-establishes bore fit and extends life through additional spool support and annular grooves.


Oversized Bypass Clutch Control Valve Kit
Part No. 73840-BK

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Worn bores in the Ford CD4E and Mazda LA4A-EL converter bypass lineup reduce TCC control and cooler flow. This results in bushing or planet failure, reduced converter clutch life from overheating and often results in codes 628/1744/1740. Slippage codes are often generated as the unit comes up to operating temperature. As the temperature rises, valve control becomes poor and excessive clearance creates excessive leakage of converter pressure.

Sonnax oversized bypass clutch control valve kit 73840-BK features a tightly toleranced sleeve and plunger valve to prevent leakage, and an oversized and improved design bypass clutch valve.

  • Plunger valve and oversized bypass clutch valve have extended spools for better support and annular grooves to prevent wear due to side-loading
  • Lubrication plugs increase lube and converter pressures by tapping into line pressure instead of depleting converter feed
  • Plunger sleeve manufactured from highly wear-resistant aluminum
  • Hardcoat anodized aluminum valves combat premature wear

This kit cannot address high line pressure in the PR balance circuit, which can break up parts and reduce flow into the converter/cooler circuits. For information on that repair, see part number 73840-RK.

  • Rivets (3)
  • Bypass Clutch Valve
  • Plunger Valve
  • Bypass Clutch Sleeve
  • Lubrication Plugs (4) 1 Extra

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.

Ford CD4E Valve Body Layout

Ford CD4E Valve Body Layout
  • CD4E, LA4A-EL Oversized Bypass Clutch Control Valve Kit 73840-BK
  • CD4E, LA4A-EL Oversized Bypass Clutch Control Valve Kit 73840-BK