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What is a transfer case and what is it for

The transfer gearbox is an indispensable unit installed in SUVs and some trucks. Thanks to him, the front and rear axles are interconnected with each other, which certainly helps in overcoming obstacles. Next, consider the design features, purpose, let's figure out how the dispenser works.

What is a car transfer box

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

Why car razdatka 

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The transfer case is especially important on the road. By locking the center differential, it connects the bridges and distributes the torque equally on the axis. For greater effect in bridges, it uses interlock differential lock. The simplest razdatka works in such a way that the redistribution of forces is carried out according to the principle “where the load on the wheel is greater”. 

For sports cars equipped with an all-wheel drive system, it was previously installed a razdatka without a downshift, which rigidly connects two axles, distributing a torque of 50:50 or in another different 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 in the case of the RCP is it possible to disconnect one bridge.

Transfer Case Device

distribution of scales

A classic transfer case with a reduction gear consists of the following parts:

  • metal casing, which is attached to the body or subframe through the pillows;
  • drive shaft - transmits torque from the gearbox to the cardan shafts;
  • center differential, which distributes torque between the axles;
  • differential lock - fixes the torque of the gearboxes;
  • chain or gear;
  • oil chamber;
  • reduction gear and synchronizer, which allows activating “lowering” in motion;
  • control mechanism (levers, servo, hydraulic);
  • gears of shafts, providing torque transmission.

The razdatka works like this:

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

Varieties of handouts

chain transfer case

By type of application, there are 4 types of manual transmission:

  • RCP with coaxial shafts - the system is widely applicable, as it allows the use of an interchangeable final drive;
  • with a misaligned driven shaft - it is distinguished by reliability, the absence of a prom shaft, due to this manual transmission is compact;
  • with a drive lock - great for off-road, however, there will be increased tire wear on the track due to slippage of one side of the wheels when cornering, to avoid this, the front axle is turned off;
  • razdatka with differential - allows the wheels to rotate at different speeds, ensuring the safety of movement on an asphalt road in 4WD mode.

Types of center differential

According to the locking mechanism, the transfer gearboxes are divided into several categories:

  • Haldex friction multi-plate clutch - works automatically 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 disks and silicone fluid. The disks are connected to the bridges, with a difference in their rotation, the liquid becomes viscous and connects them, the four-wheel drive is turned on. 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% of torque, leaving 20% ​​for the towed axle. 

Transfer Case Management

transfer case lever

With a hard connection of the Partime bridge, as a rule, there is a lever with four operating modes:

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

Four-wheel drive shift modes:

  • 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 was replaced with a washer, and the servo drive is responsible for switching on the modes, and the integrated transfer case control unit helps to choose the necessary mode, depending on many factors.

Major faults

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:

MalfunctionAs manifestedHow 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 gear 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
Working out on the teeth of couplings and gears, broken or lost properties of the spring on the clamps, the drive elements are deformed or broken, a depletion has formed on the splines or gears of the box, the gaps in the mount of the transfer case have increased, the gear transmission of the drive is worn or its adjustment is 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.

Questions and answers:

What is the difference between a transfer case and a gearbox? The gearbox is installed in all vehicles. The distributor is installed only in four-wheel drive cars for even distribution of traction along the axles.

What is the function of the transfer case? Depending on the type of all-wheel drive, the transfer case distributes the torque along the axles and increases it to overcome off-road conditions.

Where is the transfer case installed? The transfer case is installed after the gearbox. A shaft comes out of it, going to an additional drive axle. The transfer case with the help of a downshift is able to increase traction on the axle.

What kind of oil to fill in the transfer case? It depends on the type of transmission. The mechanical versions use transmission oil. If an automatic transmission is installed, then ATF is poured into the dispenser.

One comment

  • anonym

    But content hopelessly translated. Verify the correctness of some concepts.

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