How to check the automatic box when buying a car

Buying a used car with an automatic transmission must be taken responsibly. In this case, it is important not to make a hasty decision, but to carefully check the operation of the automatic transmission.

If you decide to buy a car with a gun, then you need to know how to identify possible defects. This article will help. It describes several methods that are best applied consistently. You should always start checking with oil.

Check oil in automatic transmission

It is convenient to assess the state of the transmission fluid using a probe. But not all machines have a design with a probe. To check the oil in this box, go with the seller to the service station. The specialist will conduct a full diagnosis and will tell you exactly what condition the automatic transmission is in.

If the box has a dipstick, then it will be possible to check its fluid yourself.It is necessary to do this in the parking mode (P) and on the engine. While the engine is running, you need to remove the dipstick from the box, wipe it with a cloth and insert it in place. Then again pull out and see the level, color, smell the smell.

Level
In a cold box, the oil should be at the “Cool” mark. And after warming up the machine to a working temperature of 65 degrees, the level will rise closer to the “Hot” mark. If it can be seen that the oil on the dipstick is less than the prescribed norm, this may indicate foaming, leakage of fluid, or poor-quality repairs.

Excess transmission fluid is harmful to the machine, as well as a disadvantage. At high speeds, the oil foams and flows through the nozzles. Subsequently, it will be less than the standard, and the internal parts of the box will overheat.

Smell
In good machine, the oil has a natural smell. If it smells of burning, it is a sign of overheating of the rubbing parts in the box. Low oil pressure in the hydraulic system causes poor compression of the friction between themselves. As a result, they slip and rub off.

This problem has far-reaching consequences due to the appearance of metal chips. Metal particles are able to clog the channels in the hydraulic block, which leads to oil starvation.Gradually, the structural elements will be erased, and the box will completely fail.

Colour
By the color of the transmission fluid can also be judged on the status of the box. With a short run, the oil gets a dark red or dark brown shade. This is considered to be a good lubricating condition.

High mileage automatic transmission on the same oil changes it to black. Such a transmission fluid loses its lubricating properties. If the oil is black, then most likely, the internal elements are seriously damaged and the machine requires expensive repairs.

Automatic gear shift check

After ensuring that the oil is in good condition, sit in the car and check the gear shift. This should be done after warming up the engine. Press the brake before changing gears. Carefully watch and listen to the operation of the machine. Evaluate the smoothness of switching and make sure that there are no jerks, jolts and delays.

1. Smoothness To check this parameter, move the lever. First turn on the rear speed, then neutral and drive mode. The first time, move the lever slowly over all gears.And in the second, repeat the switch, but at an accelerated pace.
2. Jerks, pushes, delays. The machine with defects will show its status during operation. When shifting gears, you should not feel jerks or jolts. Pay attention to the delay. In a good machine, transmissions turn on quickly. If the delay lasts more than one second, this is a sign of box wear.

Conduct "Stall speed test"

Stall speed test - held after the engine warms up to operating temperature. The test helps to identify defects in the box in drive mode (D) and reverse gear (R). During the test, the number of maximum engine revolutions with the wheels locked and the throttle fully open is determined. From these values ​​you can judge the state of the automatic transmission.

Test results for different car brands are different. Specific values ​​are listed in the service book of the machine. Wanting to test, keep in mind that it makes the machine work at the limit of its capabilities. But the stall speed test is safe and will not harm the box under the following conditions:

• test duration shall not exceed five seconds;
• the machine is initially in good condition.

Therefore, before conducting an automatic transmission test, ask permission from the seller. Failure can be interpreted as uncertainty that the machine will pass the test. And if you give your consent, stick to the below described technique.

Test technique

1. Heat the engine to 90–100 degrees Celsius.
2. Completely block the wheels, to do this, install wheel chocks, raise the handbrake and press the brake pedal.
3. Shift the transmission lever to drive mode (D).
4. Press the gas pedal to the floor for five seconds.
5. Look at the tachometer and remember the number of revolutions shown in the last second.
6. Move the machine lever to neutral (N), and release the brake pedal.
7. Check the result with the values ​​indicated in the technical book of this car.

The same testing should be done in reverse gear (R). But first, take a break for a few minutes to cool the oil in the box. To do this, let the motor idle.

Test results

1. If the test values ​​are less than the norm, then this indicates a poor state of the engine, which cannot develop sufficient power.
2. If the test result has exceeded the permissible revolutions, it indicates that the front and rear gear clutches have been erased.

Check the operation of the automatic transmission on the go

After conducting the above, preliminary checks, proceed to the test box in motion. Offer the seller a ride. Find a safe and spacious area where many cars do not drive. While driving, check out several modes of operation of the machine:

1. Smooth overclocking. Perform a smooth acceleration to 60 km / h. While the car picks up this speed, the machine should switch at least two times. If this does not happen, then the box has problems.
2. Sharp overclocking. Pay attention to the dynamics of acceleration. If the engine speed is high, but the car is slowly picking up speed, the box is slipping. A car with a serviceable automatic accelerates quickly and without jerks.
3. Sharp braking. After acceleration make a sharp braking. If the box is working, then the speed will quickly reset from the fourth to the first. At the same time jerks and delays should not be felt.
4. Enable OverDrive mode. Accelerate to 70 km / h. At this speed, the automatic transmission will engage fourth gear.Click on the OverDrive button, the machine should go into downshift mode, i.e., reset the speed one step lower. If this does not happen, then the box again has problems.

Now you know how to independently check the automatic transmission before buying a car. The above methods will help determine the overall condition of the box, save a decent amount in the future. The main thing is not to be lazy to use them and then you will find the car that will not let you down.

Video: how to determine the status of automatic transmission