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  • 2-3 Flare
  • 3-5 Reverse clutch burned
  • 4-5 Flare
  • Bind-up
  • Burnt Reverse clutch
  • Delayed Reverse
  • Ratio codes
  • Reverse slip


Oscillation of the 3-5-R clutch regulator valve causes bore wear that allows crucial pressure loss and prevents proper hydraulic actuation of 3-5-R clutches.


Recover hydraulic control and renew shift performance by reconditioning the bore and installing Sonnax oversized 3-5-R clutch regulator valve kit.


Measure small spool on OE valve to determine correct Sonnax oversized 3-5-R clutch regulator valve kit.

  • 124740-21K replaces 1.83 ratio OE valve with .335" dia. spool.
  • 124740-26K replaces 1.35 ratio OE valve with .390" dia. spool.

6F50, 6F55, 6T70 (Gen. 1), 6T75 (Gen. 1)

Oversized 3-5-R Clutch Regulator Valve Kit
Part No. 124740-21K

Replaces 1.83 ratio OE valve with .335" dia. small spool.

You need this if... View Instructions

3-5-R clutches in Ford 6F50, 6F55 and GM first generation 6T70 and 6T75 units are applied in third, fifth and Reverse gears in conjunction with other clutch packs. As the 3-5-R clutch regulator valve oscillates and strokes over time, bore deterioration results, which prevents proper hydraulic control of the 3-5-R clutch pack. This can cause flares, slipping, erratic clutch apply timing, ratio codes, bind-ups, and burnt 3-5-R clutches. Reconditioning the bore and installing Sonnax oversized 3-5-R clutch regulator valve kit 124740-21K restores normal shift operation by re-establishing the hydraulic integrity of the 3-5-R circuit.

  • Replaces 1.83 ratio OE valve
  • Annular grooves help center valve in bore to reduce future side-load wear
  • Hardcoat anodized aluminum valve combats premature wear
  • Valve
  • End 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 6T70 (Gen. 1), 6T75 (Gen. 1) Valve Body Layout

Gm 6t70 6t75 vbl

November 06, 2014

Ford 6F50, 6F55 Vacuum Test Guide

Topics: Vacuum Test Guides Vacuum Testing Transmission Ford 6F55 Transmission 6F50 Transmission

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September 30, 2005

Anatomy of a Transmission: Oil Flow in the Pump-PR-Converter-Cooler Lube Circuits

Gregg Nader

Topics: Diagnostics And Theory Transmission

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  • 124740 21k in combo
  • 124740 21k
  • 124740 21k measure

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.

  • 124740 21k test