What Causes Jerking in Automatic Transmissions?
3 Answers
Automatic transmission jerking is caused by: excessively high transmission fluid temperature leading to stubborn dirt and impurities inside the transmission, which form blockages in the valve body. This obstructs smooth solenoid valve movement, preventing proper oil pressure regulation and resulting in jerking, impact, and slippage faults. More details are as follows: 1. Lack of power during acceleration, noticeable vehicle surging and jerking at low or medium speeds, accompanied by fluctuating RPM needle on the dashboard; during medium-high speed driving when abruptly pressing the accelerator pedal, the vehicle slips with rapid RPM needle rise and distinct impact sensation. 2. Significant impact sensation when shifting from P to R or D gear, with gear clashing. Abnormal noises or even loud noises from the transmission during idling, driving, or high-load operation, accompanied by irregular, dull sounds during gear shifts. The root cause: prolonged high temperatures degrade transmission fluid's anti-wear and lubricating properties, causing wear or severe wear on transmission bearings, gears, or damage to gear side surfaces. 3. Computer displays "transmission overheating" warning during driving; or perceived excessive transmission heat after driving, even becoming too hot to touch. Cause: inability to effectively control temperature during high-load operation. If temperature rises further, the transmission begins slipping, which in turn causes even higher temperature increases.
I just dealt with a lot of automatic transmission jerking issues at the auto repair shop. It's usually caused by aging and deteriorating transmission fluid, where dirty oil affects the hydraulic shifting action. It's also common to find clogged filters during fluid changes. The solenoid valves control oil pressure, and when they stick, sudden upshifts or downshifts can cause the car to lurch forward or backward. Mechanical components like excessively worn clutch plates or excessive clearance in planetary gear sets can also lead to jerking, especially after 60,000 kilometers. When the transmission control program has bugs, it may send random shift commands, and some cars can fix this by updating the software. By the way, long-term aggressive driving with rapid acceleration and hard braking accelerates wear. It's recommended to check the fluid condition every 40,000 kilometers. If jerking occurs, don't push it—get it checked and repaired immediately.
Having driven for over a decade, I'd say 80% of automatic transmission jerks are related to driving habits. In city traffic, constantly braking and then accelerating hard causes the transmission to repeatedly shift between 1st and 2nd gear, leading to overheating. Keeping the car in D gear while braking at long red lights wears out components due to prolonged clutch semi-engagement. Uneven tire pressure can also cause the transmission to misjudge load, indirectly resulting in jerky shifts. After installing wider tires, mismatched signals between vehicle speed and wheel speed sensors can trigger this issue too. Maintaining smooth acceleration (avoiding floor-it driving), shifting to N when parked, and regular throttle body carbon cleaning all help.
