Common transmission problems include transmission fluid leaks, worn or damaged torque converters, solenoid damage and clutch problems. When the engine hesitates while driving or won't shift into gear, this typically indicates that it is time to replace the clutch, while grinding and shaking can indicate a problem with the clutch or damage to the gear synchronizers.
Low fluid levels or an improper transmission fluid thickness also causes shifting problems. Slipping out of the designated gear unexpectedly while driving, which is especially serious if the engine slips into neutral, is a sign that the link that holds the gears requires repair or replacement as soon as possible. Grinding or brushing sounds while driving usually indicate torque converter problems. Worn or damaged torque converter needle bearings can cause transmission damage or failure.
Gear slippage or slow shifting, which are symptoms of solenoid problems, may also signify low fluid levels caused by leaks. The absence of leaks typically indicates damage to the solenoid caused by low fluid levels or electronic problems. Leaks usually indicate a problem with the transmission, drive shaft or gasket seals.
Transmission fluid is usually the culprit when the car makes a bumping noise in neutral gear. To correct this problem, add or change the fluid. Worn bearings, gear teeth or the reverse idler gear can also cause a noisy transmission in neutral.