What is a transfer case and what is it for


The transfer case is an indispensable unit installed in SUVs and some trucks. Thanks to him, the front and rear axles are interconnected, which certainly helps when overcoming obstacles. Next, we will consider the design features, purpose, and figure out how the distribution box works.

What is a car transfer case

Transfer gearbox is a unit that distributes torque between the driving and driven axles, or several axles. Also, the transfer case allows you to turn off the driven axle, lower and increase the gear ratio, which means it has its own differential, which can be rigidly blocked. The main function is to increase the cross-country ability of the car where there are no roads at all.

Why is a car hand-out

What is a transfer case and what is it for

The transfer case is especially important off-road. By blocking the center differential, it connects the axles, and distributes the torque equally on the axles. For greater effect in bridges, it uses an inter-ring differential lock. The simplest razdatka works in such a way that the redistribution of efforts is made according to the principle “where there is more load on the wheel”.

For sports cars equipped with an all-wheel drive system, a transfer case without a downshift was previously installed, which rigidly connects the two axles, distributing the torque 50:50 or in another other ratio. In modern such cars, instead of the classic manual transmission, they use "imitation" in the form of an electromagnetic clutch, which triggers a slip or a sharp change in the load on the wheels. For powerful cars, four-wheel drive is needed for maximum grip and effective acceleration, and only if the RCP is used, one axle can be disabled.

Transfer case device

What is a transfer case and what is it for

The classic downshift transfer case consists of the following parts:

  • a metal body that is attached to the body or subframe via cushions;
  • drive shaft - transmits torque from the gearbox to the driveshafts;
  • center differential, which distributes torque between the axles;
  • differential lock - fixes the torque of the gearboxes;
  • chain or gear;
  • oil chamber;
  • a gear wheel of a reduction gear and also a synchronizer, which allows activating the "downshift" in motion;
  • control mechanism (levers, servo drive, hydraulic drive);
  • shaft gears for torque transmission.

The distributor works like this:

  • from the gearbox shank, the torque is transmitted to the input shaft of the manual gearbox, then to the intermediate ones due to the constant engagement of two gears;
  • the gear, located on the ram shaft, is movable, therefore, when it moves, four-wheel drive is activated;
  • four-wheel drive is activated.

Varieties of handouts

What is a transfer case and what is it for

By the type of application, there are 4 types of manual transmissions:

  • RCP with coaxial shafts - the system is widely applicable, as it allows the use of an interchangeable final drive;
  • with a non-axial driven shaft - it is distinguished by its reliability, the absence of flaps, due to this manual transmission is compact;
  • with blocking of the drive - great for off-road, however, there will be increased rubber wear on the track due to slippage of one side of the wheels when cornering, in order to avoid this, the front axle is disabled;
  • transfer case with differential - allows the wheels to rotate at different speeds, ensuring safe driving on an asphalt road in 4WD mode.

Types of center differential

According to the locking mechanism, the transfer case is divided into several categories:

  • Haldex friction multi-disc clutch - works in automatic mode when one of the wheels slips, in this case the clutches are compressed and partial blocking occurs, part of the moment is transferred to the rear or front axle. It is used on SUVs and SUVs;
  • viscous coupling is a simple but reliable design, consisting of several discs and silicone fluid. The disks are connected to the bridges, with the difference in their rotation, the liquid becomes viscous and connects them, the four-wheel drive is included. The main disadvantage is overheating and untimely reaction;
  • Torsen - used on full-fledged SUVs, where worm gears are responsible for blocking. They slip less, but transmit no more than 80% torque, leaving 20% ​​to the towed axle.

Transfer case control

What is a transfer case and what is it for

With a rigid connection of the Parttime bridge, as a rule, there is a lever with four modes of operation:

  • 2H - drive to the front or rear axle;
  • 4H or 4WD - four-wheel drive;
  • N - neutral, used to downshift;
  • 4L - the mode of use in heavy off-road, where it is required to reduce the torque, providing better traction on the wheels.

Shift modes with permanent four-wheel drive:

  • H - four-wheel drive, the moment is distributed automatically depending on the load on the wheels or axles;
  • HL - four-wheel drive + center differential lock;
  • L0 or LL - low gear with blocking;
  • N - neutral.

On modern SUVs, the control lever has been replaced with a washer, and the servo is responsible for activating the modes, and the integrated transfer case control unit helps to select the desired mode, depending on many factors.

Major malfunctions

Since the transfer case is subjected to high loads during the movement of vehicles, their elements can wear out greatly if not properly maintained.

Here are the main faults and troubleshooting options:

MalfunctionHow does it manifestHow to troubleshoot
Gears incorrectly adjusted, little lubrication, gear wearA distinct howl is heard while driving at high speedReplenish oil volume, repair front or rear differential
The centering of the transfer case and the box is disturbed, the deformation of the bolts or flanges of the couplings, poor tightening of the bolts of the transfer case and gearbox support, a malfunction of the cardan joint, its shaft is unbalanced, the fastening bolts of the engine support are loosened, the front or rear cardan is unbalanced, the center differential is imbalancedWhen the car accelerates or starts to move, vibration is felt in the floor (transmitted from the transfer case)Diagnose what reason is currently valid; balance the parts, correctly fix the mechanism supports, set up the synchronous operation of the gearbox and hand-outs
Differential satellites rotate tightly, gears jam in the center differential, destruction of the working surface of the planetary gearbox in the differential, the differential bowl is worn outNoise when cornering or when the drive wheel is spinningReplace worn parts, check gear gap
Differential is worn or incorrectly adjusted after installation, hub or housing clutch is seized, fork or stem bending, transfer case drive lever is deformed or seizedArbitrary differential lock occursCheck the oil level, adjust the mechanism, replace worn gears
Development of clutches and gears on the teeth, the spring on the clamps broke or lost the properties of the spring on the clamps, the drive elements are deformed or broken, a depletion was formed on the splines or gears of the box, the gaps in the transfer case fastening increased, the gear transmission of the drive was worn or its adjustment was brokenThere is an arbitrary shutdown of gearsCheck if the shift lever rests against foreign objects in the passenger compartment, diagnose, replace worn gears, correctly adjust the mechanism
Worn oil seals and sealsOil is leakingReplace gasket and sealing materials and seals

It is worth considering that many breakdowns are the result of a violation of the lubricant change regulations, as well as improper use of the gearbox. In addition to scheduled maintenance, if even the slightest deviations appear, it is necessary to check the tightening of the support bolts and take the car to a specialist so that a complete diagnosis of the mechanism can be carried out.

In addition, about the work and malfunctions of the handout, see the video:

Parsing of the Niva Vaz handout 21214.


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