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Automatic transmission clutches (friction discs). Automatic box: device

Automatic transmission clutches (friction discs). Automatic box: device
Automatic transmission clutches (friction discs). Automatic box: device

Recently, more and more motorists prefer automatic transmission. And there are reasons for that. This box is more convenient to use, does not require frequent repairs with timely maintenance. The automatic transmission device assumes the presence of a number of components and mechanisms. One of these are automatic transmission friction discs. This is an important detail in the structure of an automatic transmission. Well, let's look at what automatic transmission clutches are for and how they work.

automatic transmission clutches


Also, this mechanism is called friction discs. The part is a clutch element between gears. At a certain point, with the help of oil, they close and stop the necessary gear. After switching on the transmission, they close again. The mechanism consists of several parts. Which ones - we will consider below.


Examining the devicesuch a mechanism as an automatic transmission clutch package, two main components of the assembly must be distinguished:

  • Metal part. It is constantly in engagement with the body of the automatic box. The metal part of the clutches is practically motionless in the box.
  • Soft. It rotates with the sun gears of the transmission. Previously, automatic transmission soft clutches were made of pressed cardboard. Modern boxes are equipped with graphite-coated mechanisms. They withstand higher loads.
box machine repair

By the way, in the 90s, the clutch package was one-sided, without overlays. The design used separately paper and metal discs. Now they have a graphite coating, even on steel elements. Automatic transmission clutches are impregnated with oil, thanks to which they are protected from friction and overheating. Typically, a package consists of two sets of discs. First comes metal, then soft. Both alternate.

About friction lining

This item has a cellulose base. The lining of the discs is impregnated with special resins. This is necessary so that the disc has good engagement and does not slip when transmitting torque. Since the mechanism is subjected to constant loads, spiral-shaped notches can be seen along its perimeter. They are installed in the direction of movement of the disks. Thanks to them, the temperature of the clutches, which arose from friction, is significantly reduced.

Note that the smaller the notch depth, the higher the risk of burning the disc. Oil cannot pass throughgrooves as needed. As a result, the temperature reaches 400 degrees Celsius and above. By the way, the lining can be made not only on a graphite, but also on a Kevlar basis. It is less prone to wear. The manufacturers themselves do not disclose the full composition of the Kevlar lining material.

friction discs

Depending on the design, this element can be of different types. There are monolithic linings with split channels for oil drainage and elements consisting of separate segments. In the latter case, the segments are separated by seams up to the adhesive layer. Such pads are used only on expensive cars. Segment elements have a complex manufacturing technology. The pads have good heat dissipation properties. This characteristic is achieved due to the depth of the oil channels.

Clutch Adhesive

To apply this overlay to the surface of the disc, a special varnish coating is used. It includes resinous compounds having a high melting point. The pad is placed on the metal surface of the disc and pressed on.

Working principle

Automatic clutches are responsible for the same function as the clutch on a manual transmission. The elements are mounted on sun gears, each of which is responsible for a specific gear. They are placed in a common structure. The number of clutch packages can be from two (on the simplest 4-speed "automatic machines") to four (on modern 6-speed automatic transmissions).

So let's see how it worksthis mechanism. In the "neutral" mode, the automatic transmission clutches rotate freely from each other. They are impregnated in oil, but do not operate under pressure. After the driver has moved the gearshift lever to the "drive" position, the pump pressure increases. The oil in the box passes to a special channel through the valve body.

automatic transmission clutch replacement

As a result, the friction discs are pressed against each other under pressure. The desired planetary gear gear is engaged. The car starts moving. The speed of rotation of the wheels depends on the selected gear on the gearbox (in other words, on the gear on the box).


Automatic transmission friction linings must meet the following requirements:

  • Durability.
  • High thermal conductivity (should absorb oil well).
  • Heat resistance (quality clutches operate at temperatures up to 200 degrees Celsius without changing properties and characteristics).
  • Dynamic qualities. The disc pack must transmit torque with modulated slip.
  • Static qualities (high friction slip threshold).

About this resource

How long can a clutch pack last? The resource of disks is large enough. Since they are constantly running in oil, they are subject to minimal wear. With the timely replacement of the transmission fluid, the clutch resource will be 200-350 thousand kilometers. Experts focus on the regulations for changing the oil in automatic transmissions. Indeed, if the deadlines are ignored, the lubricant will quickly lose itsproperties.

automatic transmission clutches price

As a result, automatic transmission elements (including clutches) will work in the mode of increased loads. Their resource is reduced by 3-5 times. Therefore, it is so important to change the gear oil on time. On automatic transmissions, this regulation is 60 thousand kilometers (does not apply to transmissions with a dry clutch). Both full and partial replacements are made. Experts recommend using the first option. At what temperatures does the lining begin to fail? Critical values ​​for it are 140-150 degrees. Yes, the material can withstand a load of 300 degrees, but only for a fraction of a second. Then the paper begins to crumble and burn. By the way, not only the lining suffers from this, but also the thrust discs.


Is it possible to restore such a transmission as an automatic transmission? Clutch repair involves a complete replacement of the disc pack. It makes no sense to restore them (the same as repairing brake pads). What is the price for automatic transmission clutches? The cost of a new package starts from 8 thousand rubles, and this is without taking into account the work. Such a service as the replacement of automatic transmission clutches costs in Moscow from 10 thousand rubles.

automatic transmission clutch package

Moreover, they do not change individually, but as an assembly, as a whole package. Having learned the cost of the work, you will understand why it is so important to change the transmission fluid on time. ATP oil, although it costs an order of magnitude more expensive than usual, however, this price cannot be compared with the repair of a burnt box. If the automatic transmission is serviced on time, it will not need repairs forover two hundred thousand kilometers.


So, we found out what automatic transmission friction discs are. As you can see, this mechanism performs far from the last function in the operation of a mechanical box. And in order to protect it from wear, it is recommended to follow the oil change schedule. Dirty grease is the main enemy of friction discs. Also note that this clogs not only the filter, but also the radiator. As a result, the box is constantly overheated.

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