What Are the Symptoms of a Faulty Gearbox?
3 Answers
The gearbox, commonly referred to as the transmission, can exhibit numerous symptoms when damaged. For example, difficulty in shifting gears, failure to move when in D gear, and jerking sensations. Below is extended information on different types of transmissions: AMT Transmission: This is one of the earliest automatic transmission technologies. Its structure is similar to a manual transmission but includes an additional control mechanism to assist the driver with clutch operation and gear shifting. The most common issue with this transmission is control mechanism failure, which can result in the inability to shift gears or move when in D gear. AT Transmission: Also known as a torque converter transmission, this is the most mature and widely used automatic transmission. It primarily relies on hydraulics for gear shifting and contains numerous solenoid valves and oil passages. The most frequent problems with AT transmissions are solenoid valve failures and oil passage blockages, the latter often caused by prolonged neglect of transmission fluid changes. Dual-Clutch Transmission (DCT): Often referred to as DCT, this transmission is structurally similar to a manual transmission but features two sets of clutch plates. It offers fast gear shifts, high transmission efficiency, compact size, and lightweight, making it the most popular transmission today. Common issues include clutch overheating or internal control mechanism failures. Dry-type dual-clutch transmissions are particularly prone to clutch overheating. CVT Transmission: Known as a continuously variable transmission, it lacks gears and instead uses two pulleys and a steel belt for speed variation. CVT transmissions generally experience few problems. However, over time, the steel belt may slip. Additionally, CVTs are not suitable for high-power engines, as this can easily lead to belt slippage.
I've repaired many cars with transmission issues, and the most obvious symptom is sudden jerking during gear shifts, as if someone kicked the car from behind. When accelerating, the engine revs but slips, and even with the pedal to the floor, the speed won't increase, accompanied by a burning smell. Noise problems are particularly common—the transmission hums at low speeds and makes terrifying clunking sounds when turning. A lit dashboard warning light is basically a confirmation signal; at this point, the transmission may enter protection mode, locking the vehicle in a single gear. Even worse, reverse gear often gets stuck, requiring repeated engine restarts. If these signs appear, don't push your luck—head to a professional repair shop immediately, or the cost of a full transmission replacement could be half the price of a used car.
That time when my car's transmission failed really scared me. In the morning when I started the car and shifted to D gear, it just wouldn't move. Repeatedly stepping on the gas pedal only made the engine roar. On the highway when overtaking, it suddenly lost power, and the truck in the rearview mirror almost rear-ended me. Later, driving in the city, I found the car shaking like a sieve when shifting gears, and starting from a red light was so slow that cars behind me honked furiously. The strangest thing was the tachometer needle jumping wildly while the speed stayed stuck at 30 mph. When I parked to check, I found a pool of oil under the car that smelled fishy and greasy. The mechanic said it was transmission oil leakage causing internal overheating, and if I had kept driving, the gears would have melted. Since then, I check the transmission dipstick every month and replace the oil immediately if it turns black.
