All-wheel drive and four-wheel drive systems are designed to provide the maximum amount of torque to each wheel without causing the tire to slip. All-wheel drive means full-time four-wheel drive. This system typically can’t be switched off and is designed for all types of surfaces. Four-wheel drive usually refers to a part-time system that can be switched off or on. It is meant for low-traction conditions only.
Engaging four-wheel drive causes the transfer case to lock the front driveshaft to the rear one so that each axle receives half of the torque produced the engine. This gives you better traction than a two-wheel-drive vehicle; the downside is that it can also create a safety issue under certain conditions. If one wheel is on a slippery surface, the torque to that wheel will drop to zero. And since torque is split evenly, the other wheel will also receive zero torque.
All-Wheel Drive and Four-Wheel Drive Components
The main components of all-wheel drive and four-wheel-drive system are the front and rear differentials, the transfer case, and advanced electronics such as ABS brakes and sophisticated clutches for better torque transfer. Four-wheel-drive systems also have locking hubs.
Differentials come in various types: open, limited-slip, and locking. Each kind has a different effect on how a car or truck can utilize available traction.
The transfer case is a combination of gears, shafts and drive chain that optimally splits the power between the front and rear axles.
Locking hubs are used to disconnect the front wheels from the differential and driveshaft, which lets the driveshaft stop spinning when the car is in two-wheel drive.
All-wheel drive and four-wheel drive systems are complex engineering marvels. Correctly diagnosing and repairing problems takes a trained profession. Grant Houston, the owner and chief mechanic at Denver Transmission has more than 25 years of experience servicing transmissions and drive train components on all-wheel drive and four-wheel drive vehicles. Grant provides a two-year unlimited mileage warranty on all his work.