Transfer case and parts

The transfer case is connected to the main gearbox and distributes drive torque to the front and rear axles through propeller shafts, providing all-wheel drive. A propeller shaft also connects the main gearbox to the transfer case. Depending on the configuration, the transfer case engages the front-axle drive, provides low-range gearing or incorporates a lockable centre differential. This makes it important for vehicles operating on varied terrain: excessive play, inadequate lubrication or a drive mode that has not fully engaged can damage several parts of the drivetrain.

Transfer cases are used in MAN TGS and TGX trucks and Mercedes Arocs trucks with 4x4, 6x6 or 8x8 drive, among others. Their design varies by application: a gear-driven reduction unit for heavy off-road work has different requirements for torque capacity, cooling and bearings than a transfer case in a truck used on less demanding terrain. The presence of a centre differential, differential lock or selectable low range also depends on the configuration.

Always identify parts using the vehicle chassis number together with the transfer case identification plate. Visual comparison or selection based on the model name alone is never sufficient. Check the gear ratio, flange diameters and bolt patterns, direction of rotation, mounting points, sensor configuration and actuation system. Even the same main gearbox or engine family does not guarantee a compatible transfer case: the vehicle configuration and driven axles also determine the specification.

Typical symptoms include gear whine under load, thudding when the load changes, vibration in the propeller shafts, leaks around the shaft seals, and a differential lock or low range that does not engage fully. Worn rolling bearings increase play in the input and output shafts; damaged gear teeth or dog teeth can then cause noise and shifting problems. Contaminated transmission oil, water entering through the breather and prolonged operation with a low oil level accelerate this process.

Start the diagnosis with a test drive: note which drive mode is selected and under what load the noise occurs. Then check the transmission oil level and condition according to the vehicle procedure, and inspect the drain plug magnet for metal particles. Clean the housing before locating leaks, and check the breather and flange connections at the same time. Measure radial and axial shaft play with a dial indicator and compare the readings with the specifications for the transfer case in question. Check that the actuator completes its full travel and, on pneumatically operated versions, verify the operating pressure at the shift cylinder under the prescribed test conditions. This prevents a faulty actuation system from being mistaken for internal gear damage.

Do not replace shaft seals until the condition of the shafts and rolling bearings has been established: excessive play or a worn sealing surface will otherwise quickly cause another leak. During disassembly, inspect gear teeth for pitting, dog teeth for rounded edges and housings for cracks. Fit suitable seals and bearings with the specified fits, adjust any bearing preload according to the manufacturer’s specifications and use only the specified transmission oil.

If the transfer case has operated for a long time without sufficient lubrication, or if several gears and bearing seats are damaged, replacement is often more reliable than a limited repair. Before putting the vehicle back into service, also check the propeller shaft joints, flange alignment and axle final drives: vibration elsewhere in the drivetrain could otherwise place renewed stress on the new parts. All propeller shafts must be balanced before installation to prevent vibration. Unbalanced propeller shafts cause vibrations that place additional stress on the mechanical components of the drivetrain—namely the gearbox, transfer case and differential—and can cause premature wear or damage. Technical support with identification helps prevent downtime caused by a mismatch in configuration.