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.