* Torque Converter: This is the most probable cause. The torque converter acts as a fluid coupling between the engine and transmission. If it's failing, it might not be properly disengaging when the car is stopped in Drive, causing the engine's vibrations to be transmitted directly to the drivetrain and the car body. A failing torque converter often exhibits shuddering or vibrations, especially at low speeds or when stopped in Drive.
* Transmission Mounts: These rubber mounts isolate the transmission from the car's chassis. If they're worn or broken, the transmission can move excessively, transferring vibrations more readily to the car body. This would be felt in Drive, Reverse, and potentially even while accelerating.
* Engine Mounts: Similar to transmission mounts, worn engine mounts can allow the engine to move and shake more than it should, leading to increased vibrations felt throughout the car, especially when the engine is working against the resistance of the transmission being engaged in Drive.
* Driveshaft Issues (less likely): While less probable given the specific circumstance (only in Drive), a severely unbalanced driveshaft or a problem with the universal joints *could* contribute to vibrations, but it's less likely to be isolated to only when stopped in Drive.
* Exhaust System: A loose or damaged exhaust system could resonate and amplify vibrations, making them feel worse, but usually it would be a more constant vibration not specific to Drive.
What to do:
1. Don't drive it extensively: Continued driving with a severely shaking car could worsen the problem and potentially cause further damage.
2. Professional Inspection: Take your Galant to a trusted mechanic or transmission specialist. They can diagnose the problem accurately. Describe the symptoms precisely – the shaking only happens when stopped in Drive, not in Neutral or Park. This information is crucial for them.
3. Avoid harsh acceleration or braking: This can exacerbate any existing drivetrain problems.
The torque converter is the most likely suspect given your description, but a proper diagnosis is essential to pinpoint the exact cause and ensure the right repair. Ignoring the problem could lead to more extensive (and expensive) damage down the line.
