• TCC codes
  • Excess TCC slip RPM & related codes
  • Low converter pressure
  • Overheated converter
  • Flare shifts
  • Harsh shifts
  • Rough idle in Reverse


The bypass clutch control valve controls TC clutch apply and release pressure. As the bore wears, the apply rate of the clutch slows and the clutch release pressure will not vent.


Ream the bore to restore tolerance and install the upgraded valve and end plug.

ZF6HP21, ZF6HP28, ZF6HP34

Oversized Bypass Clutch Control Valve Kit
Part No. 95740-73K

ZF valve name: WD-V

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Common problems in vehicles equipped with ZF6HP21/28/34 (Generation 2) transmissions include an overheating torque converter, low TCC release pressure, torque converter clutch slip and firm shifts. One cause of these problems is a worn out bypass clutch control valve, resulting in slow apply and release of the TC clutch. Installing the Sonnax oversized bypass clutch control valve kit 95740-73K restores the factory torque converter clutch apply and release rates.

  • Kit fits either M-shift or E-shift valve bodies
  • Additional valve spool length at the balance port for better sealing
  • Valve is hardcoat anodized to reduce wear
  • Annular grooves for better centering the valve in the bore

Kit is NOT compatible with ZF6HP19/26/32 (Gen.1) units. To differentiate between Gen. 1 and Gen. 2 valve bodies, see ZF Identification Guide.

  • Valve
  • End Plug
  • O-Rings (2) 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.

ZF6HP21/28/34 (Gen. 2) Valve Body Layout

ZF6HP21/28/34 (Gen. 2) Valve Body Layout
  • ZF6HP21, ZF6HP28, ZF6HP34 Oversized Bypass  Clutch Control  Valve Kit 95740-73K

You need this if...

Vacuum tests at the ports indicated fail to hold the recommended minimum in-Hg.

ZF6HP21, ZF6HP28, ZF6HP34 Oversized Bypass  Clutch Control  Valve Kit Vacuum Test Locations