What are automatic transmission friction clutches and how do they work?

Peculiarities of automatic transmission friction clutches operation

It is a common belief in the auto sphere that one of the frequent breakdowns of automatic transmissions (automatic transmission) is the problem of friction discs, namely their wear and tear. And this happens even if the driver takes good care of his car, changing oil on time.

The device of automatic transmission

At this problem, malfunctioning of automatic transmission gears is observed. Many drivers don’t even realize that friction clutches are important for the transmission as a whole. This article will help to understand what automatic transmission friction clutches are, the peculiarities of their work and what can be the reasons that lead to their withdrawal.

What are automatic transmission friction clutches?

Automatic transmission friction is a device related to the clutch and plays an important role during the inclusion, as well as the transfer of torque. At one moment, these elements perform clutching, which is done by means of oil pressure, this in turn causes the pinion to stop when needed. At another moment, they open, and the pinion begins to run again.


Friction clutches are divided into the following types:

  • Single-sided. These devices are steel on one side and have a special overlay on the other. Usually these friction clutches can be found in older automatic transmissions.
  • Double-sided. Considered to be the most popular elements. For their manufacture, a strong metal alloy is used. Due to the absorption of oil by the linings, an effective heat removal from the discs is performed, which are actively heated in the working state. Such pads can be made from a variety of materials, but most often the manufacturers give preference to graphite fiber. This is due to its ability for a long time to retain performance features. In addition to absorbing heat, these pads do not burn even during exposure to extreme temperatures. In addition, the graphite pads extend the life of the discs.

It is important to note that the driver can buy the pads himself and install them without any help.

Friction clutches inside automatic transmissions

Discs are also divided into metal and soft. The first are meshed with the body of the automatic transmission, and the second carry out the rotation simultaneously with the gears. For the second kind used to be used pressed cardboard, but now more use graphite sputtering.

Principle of operation

When the gearbox is off, there is free rotation of the discs, because at this time there is no pump pressure and the frictions themselves are not clamped. However, when the gearbox is engaged, the oil pump builds up pressure which is directed to a special channel by the hydroblock and the discs begin to press against each other. This activates the necessary gear while the others are forced to stop.

Simple starter, schematic

Friction disc life

Automatic friction discs are characterized by a long service life, and this is affected by the rotation in the oil fluid. There are no exact figures for the resource, but experts suggest that it is about 350-500 thousand km, subject to competent and timely maintenance of the car. Thus, if not to change oil, wear will occur much earlier, even up to 100 thousand km.

Causes of friction failure

According to the auto experts, after 100-150 km the car owner will start to notice the malfunction of friction clutches. This may be indicated by delay, sharp jerks, which are observed during shifting of automatic transmission. To diagnose friction wear you need to climb into the gearbox, which causes some difficulties.

Among the main causes of friction disruption are the following:

  • Contaminated oil. Usually manufacturers recommend changing their oil every 60 thousand km of run. After that about 50% of oil properties are lost, and then it begins to stick, it becomes contaminated, which as a result hinders the passage of oil through the channels of the hydroblock and pump. And because of the drop in pressure, the discs start to burn, which is why in this breakdown the driver smells burnt. If you ignore oil changes, the car at 80-100 thousand km mileage has these problems.
  • Insufficient oil level or dirty oil filter. This causes the same problems as the previous reason.
  • Water gets into the oil. In this situation, rapid destruction of soft friction linings is observed, we are talking about those made of pressed paper. For example, such a problem can be in recessed cars.
  • The radiator is clogged. Circulation of oil is disturbed and acquires a thick consistency. The result of the problem will be a complete failure of the automatic transmission.

The list can also be supplemented by prolonged slipping, dynamic driving, etc.

Friction Clutches

When friction discs need to be replaced

It is very important for every car owner to realize that it is very dangerous to operate a car that has worn out and burned out friction clutches. And there are reasons for this:

  • Adjacent pistons, drum and bushings can overheat.
  • The adhesive layer of the lining can get into the oil fluid, which also causes pressure drop, oil thickening, bushing friction deteriorates, valve plates wear out, etc.
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The above problems can cause the car to suddenly stop, which as always happens at the most inopportune moment.

There are quite a few signs indicating the failure of friction clutches. If they occur the driver should take urgent measures in order to avoid serious consequences. As for the signs, you should be alert if:

  • The oil becomes dark and has an odor of burning.
  • A drop in lubricant level is detected with a dipstick or test tube.
  • The gear selector is in neutral but the vehicle is still moving.
  • Difficulty with gear shifting appears.
  • Rear drive mode has failed.
  • Vehicle begins to jerk and kick when shifting gears.
  • There is a metallic noise when idling.

First aid for automatic transmission with damaged friction clutches

When the owner of the car has found the causes of friction clutch damage listed in the previous section, he should take the following measures:

  1. Immediately stop the vehicle.
  2. Call a tow truck, since continuing to drive the car in this condition may result in more expensive repairs.

In order to carry out an accurate diagnosis of the car, experts recommend entrusting this matter to the workers of specialized technical inspection stations. It is worth noting that if the car is still under warranty, it should be sent to the official dealer, where they will help to eliminate the existing problems.

Burned clutches

If the driver has the necessary skills to repair the car, it is allowed to solve the issue independently. Before you begin to replace the friction discs yourself, you need to clean the room to prevent possible ingress of dust and dirt into the elements of the automatic transmission. For successful work, it is better to use a quality repair kit, which will fit specifically for your car. Usually such a kit consists of discs, gaskets, seals, filters.

The stages of automatic transmission repair are as follows:

  1. The oil is drained. This is possible with the help of a drain hole or a hose disconnected from the radiator.
  2. The box is removed. Because of its considerable weight, it is recommended to use a transmission jack.
  3. The disassembly of the automatic transmission is carried out.
  4. All elements from the kit are installed.
  5. The box is assembled and installed.
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These actions will not cause difficulties, the main thing is to adhere to the correct sequence. Another important point: after assembly, oil is poured a little more than the maximum level, focusing on a special marking, and then the car is started and its running-in is performed.

Important! Such repair at home should be performed only with 100% confidence in your abilities, otherwise unskilled actions lead to even more significant problems.

Frictions of the automatic transmission. What are they, how do they work and why do they burn?

The most frequent breakdown of automatic transmission is a deterioration of frictional disks or simply – friction clutches. It happens in any case, even if you take care and timely (correctly) change oil (the truth will happen a decent mileage of 300 – 450 000 km). If they have burned out, the transmission of the car will not engage or slip (about this below). Not many people know about these discs, but they are a very important element in the structure of the whole box. If it is possible to “put it crudely” this is a peculiar clutch of automatic transmission, these elements contribute to activation of this or that gear. Personally, I have long searched for a simple intelligible article on these disks, but could not find, so for a general understanding decided to write this article …

Transmission friction clutches


Let’s start with a definition.

Friction discs (friction discs) are a clutch element between gears, similar to a manual transmission. At a programmed moment they close (with oil pressure) and stop the desired gear, at another moment they open – the gear starts to rotate.

clutch analogue


These are essentially ordinary discs, which are divided into two components:

  • Metal. They are always in mesh with the housing of the automatic transmission, almost always not moving.
  • Soft discs. Which rotate with the sun gears. They used to be made of pressed cardboard, now they’re starting to be made with graphite sputtering more and more often.

It’s also worth noting that in the old automatic transmissions, friction discs were only one-sided, that is, there was no lining on them – a metal disc and a paper one separately.

friction disks

Now in modern automatic transmissions, sophisticated discs appear, even the metal has graphite overlays on the sides. They are impregnated with oil, and effectively dissipate heat from the metal disc, and help extend the life of the soft disc.

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These discs are dialed in packs, which means one metal disc, one soft disc, and so on several times. In conventional 4-stage machines, there can be two or three such sets, it all depends on the device.

Principle of operation

As I noted above, these are essentially analogous to the clutch on a manual transmission. They are mounted on so-called sun gears, each of the gears is responsible for the transmission. The automatic has a different concept of operation, here the so-called planetary gears do all the work, with the solar gears working in conjunction with them.


There are about as many gears as gears, but they are not located separately, as say on the mechanics, they are assembled into a general design. It’s also worth noting that in a 6-speed transmission, there can be two planetary gears and about 4 to 5 friction packages.

So how do they work?

If the transmission is off, the friction discs rotate freely, there is no pressure from the pump and they are not jammed. But after the transmission is engaged, the oil pump creates pressure, it passes through the hydroblock to a special channel and the disks are pressed against each other, thus the desired gear is activated and the others are stopped. This is not easy to understand, especially for a beginner, so there will be a detailed video below where you can see the principle of action.

friction diagram

In any case, you need to understand – these particular discs are a very important element in the work of the entire automatic transmission as a whole, without them there was no principle of automatic transmission.

Friction discs resource

The discs themselves have a fairly long lifespan, I’m even now afraid to speculate. They rotate in oil (ATF fluid), not air, so the life span is really huge.

Personally, my opinion is a minimum of 350 thousand kilometers, and as a maximum of 500 thousand, after all, nothing is everlasting!


But if you do not change the lube on time, or do not change it at all, and rely on the name – the automatic machine maintenance-free (though it’s nonsense). They can break down after a small mileage, do not even till 100 000 km. So the oil is really a decisive factor for them. Why? Let’s read on.

Causes of failure

There are not too many of them and they are all related to the ATF fluid in the automatic transmission. Let’s list them point by point:

  • Dirty oil . The majority of manufacturers, regulate replacement in its automatic transmission at about 60,000 km run. However, now the so-called maintenance-free automatic machines are appearing, and the owner relaxes and does not change it at all! That is why problems appear already at 80,000-100,000 km. But why? “Transmission” is a complex mechanism, as we have already figured out with you, there is a lot going on here from oil pressure, the life of its work is just 60,000 km, after that it already loses its properties by about 30-50%. It starts to stick, a lot of dirt and chips are formed in it (because the filter is also clogged), and at the end it cannot normally pass through hydraulic cylinder and oil pump channels. The pressure drops, it is no longer able to squeeze the friction discs, and they banal begin to slip against each other – just burn! That’s why the oil smells burnt, at this failure – just from the disks.
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old and new oil

  • Insufficient level . If the fluid level for the “automatic”, will not be sufficient, it will lead to a similar situation described in the first paragraph.
  • Clogged oil filter. If the filter is clogged, oil can not pass through it, pressure drops. The discs slip – they burn.
  • The radiator. From dirty oil it gets clogged, the fluid can no longer circulate in it, and therefore is mostly in the operating zone. From high temperatures (and they can reach up to 150 degrees), it burns, becomes thick and simply kills your automatic.
  • Water ingress. Rare, but it happens, for example in sinking cars from the “West”. If water gets into the oil, it very quickly destroys the soft friction linings, because they are made of pressed types of paper and are just afraid of water.

These are the main causes of these discs failing, as you can see 4 out of 5 points are related to the ATF fluid of the automatic, or rather the timely replacement of it.

Once again I will emphasize – guys change oil in automatic – MUST! AND DO IT CORRECTLY! Then this transmission will please you not one hundred thousand kilometers.

Now watch the video version, it explains more in detail.

Goodbye at this point, read our AUTOBLOG.

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