Possible causes of impact when engaging reverse gear in a BMW automatic transmission:
1. Faulty torque converter lock-up clutches
* Worn or damaged clutches may create a shock when engaging reverse gear.
2. Low transmission fluid level
* Insufficient fluid may result in insufficient pressure, resulting in shock.
3. Contaminated transmission fluid
* Contaminated fluid may prevent components from moving freely and cause shock.
4. Faulty gear selector position sensor
* A faulty sensor may give incorrect readings about the current selector position, resulting in bumps or failure to engage reverse gear.
5. Worn or damaged solenoids
* Solenoids control the flow of fluid into the automatic transmission. Worn or damaged solenoids can create a knock or make it difficult to engage reverse.
6. Faulty hydraulic modulator
* The hydraulic modulator controls the fluid pressure in the automatic transmission. A faulty hydraulic modulator can cause shock when shifting gears.
7. Worn or damaged transmission gears
* Worn or damaged gears can create noise and shock when shifting gears.
8. Faulty transmission control module
* The transmission control module controls the electronic components of the automatic transmission. A faulty module can lead to incorrect operation of the automatic transmission and shocks.
9. Electrical problems
* Poor connections or faulty wiring can cause shifting problems and shock.
10. Incorrect clearances in the gearbox mechanism
* Incorrect clearances between automatic transmission components can lead to shock when shifting gears.