Checking the automatic transmission for defects

An automatic gearbox is perhaps the most complex and expensive part of a car. It will be very expensive to repair it in the event of a serious breakdown. Therefore, it is useful to know what to look for and how to determine the condition of the automatic transmission in order to identify possible problems at an early stage and avoid unnecessary financial costs. In addition, it is very important to correctly diagnose the automatic transmission when buying a car with an automatic transmission in the secondary market. If the operation of the transmission is in doubt, you can bargain and reduce the price or completely abandon the purchase. Otherwise, the unsuccessful purchase of a car with a problematic automatic transmission may soon result in considerable repair costs.

When buying a used car, you should be very careful. It is better if a detailed diagnosis of key components, including the gearbox, is done by specialists. But this is not always possible, and then you have to diagnose everything yourself.

First you need to conduct a thorough general inspection of the machine. The general condition of the car can tell you how difficult the conditions were in which he had to work.

Pay attention to whether there is a tow hitch (hitch). Its presence is not a very good sign, indicating that the car could carry a trailer with loads, which means that the internal combustion engine and transmission were subjected to increased loads and wear. The towbar itself can be removed, but take a closer look - there may be traces left in the place where it was installed.

Ask the owner in what conditions the machine was operated, how it was serviced, what repairs were made.

If the car worked in taxi mode, then in this case it can be assumed that the automatic transmission is seriously worn out, which means that its repair shines in the near future.

If the box was repaired, this in itself is not a negative factor. After a quality repair, an automatic transmission can function normally for a long time. But ask the owner when and why the repairs were made, what specifically changed. Ask for supporting documents - checks, acts of work performed, marks in the service book, check if there is a guarantee. The absence of such documents should alert, as well as the fact that the owner has just repaired the automatic transmission and is now selling it.

Find out how regularly the automatic transmission was serviced, when and for what reason the oil was last changed, what kind of liquid was filled in - the original or an analogue.

Compare the data obtained with the total mileage of the car. Under normal operating conditions and regular maintenance (every 50 ... 60 thousand kilometers), a classic automatic transmission runs an average of 200 ... 250 thousand kilometers, a robot and a variator - about 150 thousand. Lack of maintenance reduces the working life of the automatic transmission by 2 ... 3 times.

If a general inspection and conversation with the seller did not discourage you from purchasing this car, you can proceed to further verification. A 100% diagnosis of automatic transmission can only be made at autopsy. And only primary diagnostics is available to you, which includes checking the level and condition of the oil, the control cable and the behavior of the automatic transmission in motion.

If the gearbox has built-in sensors that monitor pressure, temperature and other parameters, they will help assess the general condition of the automatic transmission, but will not eliminate the need to check the operation of this unit.

The initial diagnosis of an automatic transmission when buying a used car is not fundamentally different from the check that you can carry out on your own car.

Unlike a manual or robotic gearbox, in a hydromechanical automatic gearbox, oil does not just act as a lubricant, but is a working fluid involved in the transmission of torque. The inclusion of a particular gear occurs by means of the pressure of the ATF fluid on the corresponding clutch packs. Therefore, the quality of ATF oil and its level in an automatic transmission are subject to more stringent requirements than for transmission lubricant in a manual transmission.

Jerks or kicks at the time of gear shifting may indicate an insufficient or excessive level of working fluid in the automatic transmission. It is the wrong oil level that is most often the root cause of serious malfunctions in the automatic transmission.

The level measurement procedure may have its own nuances in different models of machines, so first of all you should look into the service manual.

In general, the rules for checking the oil level in automatic transmissions are as follows.

The engine and gearbox must be warmed up. To reach the operating temperature level, you need to drive 15 ... 20 kilometers.

Stop on level ground and engage P (Parking) mode. Do not turn off the engine, let it run for a set of minutes at idle. For some car models, the measurement is made with the engine turned off, and the switch handle must be in the N () position. This should be stated in the user manual.

To prevent debris from getting inside the automatic transmission, wipe the neck, then remove the dipstick and blot it with clean white paper. Assess the quality of the liquid. Normally, it should be transparent and have a pink color. If the oil has been in use for some time, it may darken slightly and acquire a light brown tint, this is a correct phenomenon. But brown or black color indicates that the liquid has overheated. The presence of dirt or metal chips indicates serious wear. And if there is a smell of burning, it means that the friction clutches are slipping and probably worn out. A high degree of wear means that the box will soon need expensive repairs.

Wipe the dipstick with a clean, lint-free rag and reinsert it for a set of seconds, then remove it again and diagnose the ATF oil level. In some models, the probe has only one mark, but, as a rule, there are two of them - Hot and Cold. The level should be in the middle, without significant deviations in one direction or another. Both high and low fluid levels are equally harmful to automatic transmissions. If there is a significant deviation and the level is close to the COLD or HOT marks, you need to add or pump out excess oil.

If the fluid is old and dirty, it must be replaced. Do not forget that the ATF oil must meet the requirements of the automaker for this model, otherwise the automatic transmission will not function normally and may fail. At the same time as the oil, the automatic transmission filter should also be changed.

The situation is more complicated with the so-called maintenance-free boxes, in which there is no oil dipstick. In this case, it will not be possible to determine the level of the working fluid, but you can at least evaluate the smell. Although formally an oil change is not provided for in such a unit, in fact it is worth changing it periodically in order to extend the life of the box. To check such an automatic transmission, you should contact service specialists.

The adjustment cable gradually wears out, its adjustment is disturbed. Normally, the cable should not have free play. But often it sags, as a result, the gears can switch too quickly, at the moment of switching, double jerks and slips will be felt. The transition to kick-down mode, which is activated when the gas pedal is pressed all the way down sharply, will occur with some delay and a slight jerk.

Those who prefer an aggressive driving style often pull the cable harder. In this case, the kick-down mode is activated with a sharp jerk and without the slightest pause. And gear shifting with a smooth press of the gas pedal will be delayed and tangible jolts.

The vehicle repair and maintenance manual usually describes the adjustment procedure in detail. Each motorist can adjust the cable according to their preferences. However, not everyone has the skills and patience, because you need to adjust a little, and then drive for some time, checking how the gears switch from lower to higher and vice versa. An excessively loose or overtightened cable may interfere with the proper functioning of the automatic transmission. If you do not pay attention to this for a long time, the automatic transmission will wear out at an accelerated pace.

After the transmission has warmed up, stop the car on a level surface, press and move through all positions of the gear selector. First move the lever and hold each position for a set of seconds. then do the same quickly. A slight twitching during shifting is quite acceptable, in contrast to strong jolts, which indicate incorrect operation of the automatic transmission. There should also be no significant delays in gear engagement, vibration or extraneous noise.

diagnostics on the road will provide an opportunity to test the operation of the transmission in various real modes. To do this, you need to find in advance a suitable, sufficiently long and even section of the road.

Engage D (Drive) mode and accelerate smoothly from a standstill. As you accelerate to 60 km / h, at least two shifts should occur - from 1st to 2nd gear, and then to 3rd. Switching should occur with minor shocks. The engine speed should be within 2500 ... 3000 per minute for a 4-speed automatic transmission or about 2000 for a 6-speed automatic transmission. If the automatic transmission is working, there should be no strong shocks, jerks and delays in gear shifting, as well as suspicious sounds.

Try to accelerate sharply to diagnose acceleration dynamics. If the engine speed is high, but the car does not accelerate well, then this indicates a probable slipping of the clutches in the box.

Next, apply gentle braking to check the downshift. Here, too, there should not be strong shocks, jerks, delays and an increase in the speed of the internal combustion engine.

When braking hard, the transition to 1st gear should occur without jerks and delays.

The checks described above will help make a further decision. If you are the owner of the car, you can decide whether your automatic transmission needs more detailed diagnostics with the help of car service specialists.

If we are talking about purchasing a used car, then depending on the results of the inspection, it will be possible to make a decision to refuse the purchase or to make a reasonable bargain. If the test results satisfy you, then you should go to a service station and conduct a more detailed diagnosis of the automatic transmission, internal combustion engine, and other components of the car to be sure that the purchase will not bring you disappointments.