How a Ford 4WD Worksby Rachel Steffan
Ford four-wheel-drive (4WD) systems allow a vehicle's engine to send power to all four wheels, instead of the front wheels or rear wheels only. Many 4WD vehicles can be switched back and forth between rear-wheel drive using a switch or a gear lever in the cab. Some require lock-out devices on the front hubs to be turned manually to engage four-wheel drive.
Ford four-wheel drive systems rely on a transfer case adjacent to the vehicle's transmission and the front output shaft that powers the front wheels when four-wheel drive is engaged. The transfer case switch is actuated either physically or electronically by controls in the passenger area. Some systems use locking hubs on the front wheels to engage the front axle and differential when four-wheel drive is in use but disengage it when the vehicle is in two-wheel drive, thus saving wear and tear on components in the front end.
Ford began offering the outsourced "Marmon-Herrington All Wheel" system on it's new line of F-Series trucks in 1948, utilizing technology developed for military vehicles during the Second World War. In 1959, it brought four-wheel drive production in-house, with several systems available over the years, notably the Borg-Warner Control Trac and Control Trac II and the Haldex Traction. Four-wheel drive was limited to trucks and SUVs until 1986, when the 4x4 Ford Scorpio passenger car was introduced.
Difference from AWD
Four-wheel drive is not the same as all-wheel drive (AWD). Four-wheel drive vehicles have an option called low range that sends more torque to the wheels but at lower speeds. Many also have a neutral option in the transfer case that disconnects all four wheels from the engine. All-wheel drive vehicles can't be switched back and forth between two- and four-wheel drive, nor do they have low-range or neutral options.
Older Ford four-wheel-drive systems like the Borg Warner Control Trac I cannot be used on dry pavement without damaging the drive train. As the vehicle turns and changes speed on dry pavement, stresses build up between the different wheels, causing wheel jumping and torsion on the drive shaft and axles. Some systems also lose power to the gripping wheels when one or more wheels lose traction.
- Golden Gate viewed from the truck image by Alex "Stranger" from Fotolia.com