Transfer Case Basics
A transfer case is part of the drivetrain system in four-wheel-drive and some all-wheel-drive vehicles. Its primary function is to engage the secondary axle, normally the front axle, of your truck or 4 x 4. The T-Case, as it’s often called, is typically positioned underneath the vehicle, behind or beside the transmission. It consists of a case, or housing, made of aluminum or cast iron, containing a complex system of gears, chains, and/or belts. The transfer case works by engaging or disengaging the secondary axle. When engaged, the T- Case transfers the engine torque from the transmission to both the front and rear output shafts. The output shafts connect, via slip yokes and universal joints, to leading to the front and rear differentials, and from there to the drive axles and ultimately to the wheels.
Most transfer cases can mechanically lock the front and rear together, so each axle gets an equal amount of engine torque. More advanced T-Cases can electronically adjust the percentage of torque between front and rear axles. Sometimes the vehicle will have a manual override for this function but it’s primarily done with an electronic control module. This may be a stand-alone T-Case control module but it’s more often part of the Powertrain Control Module or the Transmission Control Module. These modules may require reflashing from time to time as vehicle manufacturers develop better software that improves drivability, durability, or fuel economy.
Why is Transfer Case Fluid so Important?
Transfer case fluid is either synthetic or traditional organic gear oil, and like many other vehicle systems certain T-Cases need certain types of fluid. This is because the fluid has several functions and must work in conjunction with the mechanical design to ensure optimum performance and longevity. Transfer case fluid removes heat and lubricates the internal parts of the transfer case to keep its gears and bearings cool and lubricated so they turn smoothly and don’t expand or distort too much due to heat.
With usage, transfer case fluid becomes contaminated with minute metal particles as the gears and other metal components wear down. These particles in the fluid eventually become a sort of grinding compound that wears down the gears, bearings, shafts, chains, etc. even faster. The fluid also breaks down due to heat, and loses some of its friction reducing properties and its viscosity (the ability to stick to metal components to lubricate them). This may affect a vehicle’s performance, causing it to shudder or emit whining sounds under certain drivetrain loading conditions. If the fluid runs low or becomes contaminated it will eventually lead to failure of the T-Case.
Transfer cases do not have any fluid filter or fluid cooling system. Replacing the fluid periodically is the only way to remove contaminants and restore the lubrication properties.
How Often Should a Transfer Case be Serviced?
To avoid all of the above issues, it is recommended that the transfer case fluid be changed regularly with the manufacturer’s specified fluid. For normal driving this means every 50,000 Km. If you are towing heavy trailers and using four-wheel drive frequently you should consider T-Case service every 25,000 Km. So, while it may be seem more economical to wait till 100,000 Km to change the transfer case fluid, waiting could cost a lot more than regular drivetrain service.
Wheel and Tire Sizing – CRITICAL
When a transfer case is locked in four wheel drive it typically splits the engine torque evenly between the front and rear axles. Unlike a differential, most T-Cases can not automatically adjust torque between the two axles. This means that if your tire diameter on the front wheels is different from the rear, something has to give. In this situation you will get tire slipping/skidding against the road because none of the driveline components allow for any slip. This isn’t a big deal if you’re plowing through mud or snow, but on dry pavement it causes enormous stress on your transfer case and universal joints, and usually results in whining noises indicating rapid wearing of components. Tire circumference is the determining factor in terms of distance traveled per revolution of the wheel, and circumference is pi (about 3.14) times the diameter. So if you have 1/4 inch less tread depth on your front tires than your rear tires, the rears will have to skid by over 3/4 of an inch (1.8 cm) for every tire revolution. This adds up to about 26 meters of skidding per kilometer of driving. If you actually have mismatched tire or wheel sizes it’s even worse than uneven tread wear and will cause significantly more tire skidding. These situations lead to massive overloading of your entire drivetrain, but are particularly damaging to your transfer case.
Bob’s Driveline is your best choice for professional transfer case rebuild and repair in Abbotsford, Langley and the Fraser Valley. We provide the best value for regular maintenance on your transfer case, and can economically repair leaks or even rebuild the entire transfer case if necessary, ensuring years of reliable service from your 4×4 vehicle. Call today to schedule an appointment.