Project Work Truck

Rebuilding The 4R100 Transmission For Towing And Hauling

- Chris Tobin

The 4R100 transmission in Vincent Uriah's 2003 Ford F-350 work truck has been a hard worker for most of its long life and despite upgrading to a triple-disc torque converter and modified valve body some time ago, the high-mileage factory clutches could not handle the heavy hauling any longer.

Unfortunately for Uriah, the heavy towing of earth-moving equipment for his concrete business, combined with the additional power the 7.3L Power Stroke engine is now making, did not bode well for the factory clutches and the transmission started to slip under load. Upon teardown, Swamp’s transmission specialist Dan Morin determined that the forward clutch pack suffered a catastrophic failure with the clutches completely self-destructing. The design and operation of the 4R100 transmission applies the clutch packs in a cumulative arrangement, meaning that the clutch packs apply and add to the previous stage to make the transmission shift gears. So once the forward clutch pack (which is engaged in all forward gears) started to slip, the clutches simply burnt themselves up, leaving the truck stranded.

Rather than rebuild the transmission to factory specs at the dealer or a local transmission shop, Uriah chose to trust the expert diesel specialists at Swamp’s Diesel Performance in LaVergne, Tennessee. They suggested upgrading the 4R100 with an Xtreme rebuild kit from Sun Coast Converters as well as their four-disc coast clutch drum and 2-3 shift valve. In addition to using higher quality Raybestos clutches and Kolene-coated steels that handle high heat better, the Sun Coast kit features machined components to allow more clutches and steels to be used in each pack for more holding power and less heat buildup. The Xtreme rebuild kit and upgrade parts will work well with the valve body modifications Morin performed previously, allowing the transmission to work well with heavy loads and engines in the 450-550 horsepower range.