What Causes the Sudden Jerking When Starting an Automatic Transmission Car?
3 Answers
Experiencing jerking when releasing the brake during start-up can be attributed to several factors. For instance, internal transmission issues, such as excessive wear leading to gaps, can cause looseness during start-up, resulting in a jerking sensation. The best solution to such problems is to replace the transmission fluid and perform a comprehensive transmission maintenance. Additionally, avoid aggressive driving in daily use to prevent accelerated transmission wear. This phenomenon is quite common in high-performance vehicles with significant horsepower, especially those equipped with AT transmissions. During rapid acceleration, the engine speed increases extremely quickly, causing a noticeable impact when shifting from 1st to 2nd gear. Particularly when the throttle is pressed hard, raising the engine speed to five or six thousand RPM or even higher, the transmission must abruptly reduce the speed from five or six thousand RPM to two or three thousand RPM to ensure smooth engine operation. This sudden reduction in speed generates the impact, which is the so-called jerking sensation. However, during rapid acceleration, the jerking sensation in lower gears becomes significantly more pronounced.
I've been driving an automatic transmission car for several years, and jerky starts are quite common. It could be due to deteriorated or insufficient transmission fluid. Dirty fluid can affect lubrication and power transmission, leading to uneven power delivery. Ignition system issues, such as excessive spark plug carbon buildup or aging high-voltage wires, may also cause engine shaking, especially during cold starts. Additionally, faulty sensors like the throttle position sensor can send inaccurate signals, causing the computer to misjudge shift points. When addressing this, first check the transmission fluid level and color—clear and transparent indicates good fluid, while murky means it's time for a change. Delaying repairs may damage internal transmission gears, which can be extremely costly. Regular maintenance, including fluid changes every 60,000 kilometers, is key to prevention. Safety first—don't procrastinate.
When I helped a customer solve this type of issue during car repair, I found that starting hesitation is usually related to the engine. For example, uneven fuel supply, clogged fuel injectors, or unstable fuel pump operation can cause incomplete fuel combustion, leading to vibrations. Severe carbon buildup can cause surging and shaking in low-speed ranges, and worn torque converters can also result in discontinuous power engagement. The solution is simple: cleaning the throttle body and fuel injectors, and replacing the spark plugs usually does the trick. I recommend that car owners use high-quality fuel to reduce carbon buildup and not ignore minor issues, otherwise, transmission repair costs could double. Driving safety is important—if a problem is detected, pull over and inspect it as soon as possible.
