Ford 5R110W (TorqShift)

Ford's heavy-duty five-speed — behind the Power Stroke diesel in the F-250 Super Duty and the Excursion.

It replaced the 4R100 and fixed that transmission's weakness, which was heat: the 5R110W adds a cooler circuit and a sixth ratio that only engages when the fluid is cold, used to warm the transmission faster. So a truck that appears to have an extra gear in winter is behaving correctly — the marketing name TorqShift covers both.

Its recurring failure is the torque converter and the fluid that protects it. These tow at their limit, and a converter that has been cooked contaminates the fluid with the material it sheds — which is why a burnt smell on one of these points at the converter rather than only at a fluid change.

The solenoid body accounts for most electrical faults, producing harsh engagement or a limp mode, and it is a serviceable assembly rather than a rebuild. An auxiliary cooler is a preventative measure on a towing truck, not an accessory.