How to check the automatic transmission box when buying a car

Buying a used car with an automatic transmission must be treated responsibly. In this matter, 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 sequentially. You should always start checking with oil.

Automatic transmission oil check

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

If the box has a dipstick, then it will turn out to check its fluid on its own. This must be done in the parking mode (P) and on the wound motor. While the engine is running, you need to remove the probe from the box, wipe it with a cloth and insert it into place. Then pull it out again and look at 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 is clear that the oil on the dipstick is less than the prescribed norm, this may indicate foaming, fluid leakage or poor repair.

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

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

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

Colour
You can also judge the condition of the box by the color of the transmission fluid. At low mileage, the oil acquires a dark red or dark brown hue. This is considered a good condition, lubricating fluid.

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

Automatic Gear Shift Check

After checking that the oil is in good condition, get in the car and check the gear shift. Do this after warming up the engine. Before shifting gears, apply the brake. Carefully watch and listen to the operation of the machine. Evaluate smooth shifting and make sure there are no jerks, shocks, or delays.

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

Conducting a "Stall speed test"

Stall speed test - carried out after warming the engine to operating temperature. The test helps identify box defects in drive mode (D) and reverse gear (R). During the test, the maximum engine speed is determined with the wheels locked and the throttle fully open. These values ​​can be used to judge the state of the automatic transmission.

Test results for different brands of cars are different. Specific values ​​are indicated in the service book of the machine. Wanting to conduct a test, keep in mind that it makes the machine work at the limit of possibilities. But stall speed test is safe and will not be able to harm the box under the following conditions:

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

Therefore, before testing the automatic transmission, ask the seller for permission. Failure can be regarded as uncertainty that the machine will pass the test. And if he gives his consent, stick to the technique described below.

Test Technique

1. Preheat the engine to 90–100 degrees Celsius.
2. Block the wheels completely; for this, install the wheel chocks, raise the handbrake and press the brake pedal.
3. Switch the automatic 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. Shift the machine lever to the neutral position (N), and release the brake pedal.
7. Check the result with the values ​​indicated in the technical book of this car.

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

Test results

1. If the test value is less than normal, then this indicates a poor condition of the engine, which cannot develop sufficient power.
2. If the test result exceeds the permissible speed limits, this indicates the erased clutches of the front and rear gears.

Checking the operation of the automatic transmission on the go

After completing the above preliminary checks, proceed to testing the box in motion. Offer the seller a ride. Find a safe and spacious area with few cars. While driving, check several modes of operation of the machine:

1. Smooth acceleration. Take a smooth acceleration to 60 km / h. While the machine is gaining this speed, the machine must switch at least two times. If this does not happen, then the box has problems.
2. Abrupt acceleration. Pay attention to the dynamics of acceleration. If the engine speed is high, but the car slowly picks up speed, then the box is slipping. A car with a serviceable machine accelerates quickly and without jerking.
3. Sharp braking. After acceleration, perform sharp braking. If the box is operational, then the speed will quickly drop from the fourth to the first. At the same time, jerks and delays should not be felt.
4. Enabling OverDrive mode. Accelerate to 70 km / h. At this speed, the automatic transmission will engage fourth gear. Press the OverDrive button, the machine should go into a low gear mode, i.e., slow down one step lower. If this does not happen, then the box again has problems.

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

Video: how to independently determine the state of the automatic transmission