Transfer case

Gearbox service

- Read general information about gearboxes here -

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» Replacement of old gearbox housing

transfer-case

What is a reducer?

A gearbox, simply put, is a circuit that distributes power from a four-wheel gearbox. We find it on all vehicles that have all-wheel drive, the so-called 4WD.

Immediately to clear two terms a to 4WD and AWD (all wheel drive). Both have all-wheel drive.

With the AWD system we have PERMANENT four-wheel drive where power is selected from the transmission to the front and rear wheels distributed in certain proportions via a central differential.

With 4WD drives, the REDUCER takes over and distributes power from the transmission to ALL or only on TWO wheels.

We will only deal with the 4WD system here.

How does the reducer work?

We said that the gearbox distributes power to the front and rear wheels, let's consider now how it does that.

The engine gives power to the transmission, which transmits the force to the gearbox, which sends power to the front and rear wheels via the output shaft. The distribution of this power can be done either through a chain or through a set of gears located in the gearbox housing itself.

Today, the chain is more used to start the gearbox because it is quieter in operation and much lighter than the gear, so it is much lighter in construction. However, it should be emphasized that gears with gears transmit more power, withstand higher torque and are less susceptible to failures.

When the driving system is not switched on in 4WD mode, the power is sent in full to the rear wheels - 2WD. When you engage driving mode, the 4WD reducer will distribute power to the front and rear wheels by driving all four wheels.

In order to distribute the power evenly, the gearbox works in coordination with the axles, differential, cardans, gearbox and wheels.

Driving speed - we usually have the marks H (HIGH which means "FAST") and L (LOW which means "SLOW")

Mode H (FAST) is used in heavy rain, mud, ice or in situations when we need additional traction.

We use the L (SLOW) mode when we need more power at lower speeds, such as when climbing on rocky or gravelly terrain or on higher ascents, especially if we are pulling a heavier load. In extreme snow or mud, etc.

Markings in vehicles are different but usually <b> 4-Hi </b> or only H or <b> 4-Lo </b> or only 4L.

Shifting is done with a lever that is usually located next to the gear lever. This is common with vehicles that are made mostly for off-road driving. In newer models, the switching is done electronically - by pressing the switch.

There are TWO MODES for 4WD

1.PART-TIME - usually marked PT - means two-wheel drive, usually rear wheels.

This is a mode where the driving conditions are met by rear-wheel drive only, which contributes to lower fuel consumption and lower stresses for the drive system.

2.FULL-TIME is switched on when two-wheel drive is insufficient and you have the already mentioned 4Hi or 4Lo modes available.

All of the above served more to understand how the gearbox works, in which situations which driving mode is used, and this only applies to off-road vehicles of all kinds that we cram into a basket from miles and out of habit, calling them JEEP.

In most modern SUVs and passenger cars, various Crossers, etc., the gearboxes engage automatically as soon as the computer registers a single-wheel slip.

Gear unit damage

The quantity and quality of oil are often neglected, which leads to damage or ignition of the blades found in all modern gearboxes.

Timely repair avoids damage to the housing when repair is not possible.

The most common symptoms of gearbox failure

  • » Constant grinding and - or whining sound under the vehicle when the vehicle is in operation.
  • » Jerk and skip in motion or ride - talks about chain damage and skipping.
  • » Damaged bearings can be easily replaced and their malfunction can be easily noticed.
  • » Black and burnt oil leaks from the gearbox
  • » Inability to switch from 4Hi to 4Lo
  • » Unable to switch from 4WD mode to 2WD or vice versa.
  • » Heavy gear shift - the gearbox interferes with the gearbox - it brakes!
  • » Oil leaks from gearbox output shaft oil seal - very common.
  • » There is no sound of the electric motor on the gear unit