Contents: Checking the switching process ↡ Checking the oil level in the…↡ Transmission oil condition ↡
The list of possible independent actions to check the functionality and repair the automatic transmission is very limited even for experienced motorists. This requires a special tool and experience in this area. Therefore, even at service stations, adjustment and repair of the automatic transmission is entrusted only to well-trained specialists. Below are simple recommendations for timely detection of faults:
Fig. 6.13. If the transmission fluid level drops, look under the car. Oil stains on the automatic transmission housing will indicate the cause of the leak
1. In case of any automatic transmission failures, first check the transmission fluid level (Fig. 6.13).
2. During a test drive, check the switching points. There are special tables for this at the service station.
3. Correct adjustment of the linkage system between the automatic transmission and the accelerator is an important component of proper operation.
4. Measuring the pump operating pressure, regulation pressure and modulation pressure is a task for specialists. Some pressure values can be adjusted.
Information copied from the website: MercedesMan.ru
5. For a correct assessment of the switching process, the idle speed must correspond to the norm.
Checking the switching process
When driving, pay attention to the automatic transmission: is it working properly? The gear shifting process gives an idea of the condition of the unit.
Shifting to higher gears. When the accelerator pedal is partially depressed, the gear change is not very noticeable. In the "full throttle" ("Kick-down") the shifts are more noticeable, but the shift to a higher gear is still smooth. A short revving of the engine to high revs when shifting indicates a possible malfunction.
Downshifting. Downshifts should be barely noticeable at low speeds (foot removed from accelerator pedal). A jerk during forced downshifting with the accelerator pedal fully or partially depressed is normal. Downshifting with the selector lever with the accelerator pedal released occurs with a delay of 1–2 s. If, however, during forced downshifting with the selector lever you simultaneously add "gas", the shift will occur without a delay.
Checking the oil level in the automatic transmission
The check is usually carried out after an oil change or if a leak is suspected. The prescribed oil level in the automatic transmission is very important for its flawless operation, so the check should be carried out with special care:
1. When the oil level is low the clutches do not close tightly enough and slip because the oil hydraulic pump captures air. The resulting foaming causes premature wear of the automatic transmission parts. In addition, the oil decomposes, becomes resinous, and sediment forms in it.
2. When the oil level is high there is increased contact of oil with gearbox parts, causing it to overheat. This leads to the same consequences as when air is sucked in due to a low level.
The transmission fluid filler hole is located in the engine compartment. The fluid level is checked through it using a dipstick.
Sequence of works
1. Apply the parking brake and move the automatic transmission selector lever to the "P" position.
2. Start the engine and let it idle for 1–2 minutes.
Fig. 6.14. Checking the oil level in the automatic transmission: 1 – transmission fluid level dipstick (located on the rear right side of the cylinder head); 2 – closing clamp
3. Remove the closing clip 2 (Fig. 6.14) above the dipstick 1, pull out the dipstick and wipe it with a lint-free cloth.
4. To measure the level, insert the dipstick with the marking facing the back (then when you pull out the dipstick the reading will not be blurred).
5. At the operating temperature of the automatic transmission (about +80°C), the oil level should be between the "MIN" and "MAX" marks.
6. When the automatic transmission temperature is about +25°C, the oil level should be no lower than 12 mm from the "MIN" mark.
7. Check the condition of the oil by color and smell - both signs allow you to judge the condition of the automatic transmission.
8. If necessary, add transmission oil. Its amount should not exceed the required level. The volume of oil between two divisions is 0.3 l. In case of overflow, pump out or drain excess oil.
Transmission oil condition
1. Clean, red color - the oil condition is normal.
2. Burnt and darkened - the clutches are burnt. The automatic transmission must be replaced, the oil lines and oil radiator must be flushed.
3. Presence of solid particles in oil (metal particles) – The automatic transmission needs to be replaced.
4. Resinous and sticky oil - the automatic transmission was often overheated. Dismantling and overhaul are necessary.