Like an engine, a transmission has oil and a filter that needs to be changed every 20,000-30,000 miles, or once every 18 months. For newer cars, you should also have the transmission flushed every 40,000-50,000 miles or every 2 years, to remove all of the sediment and debris from the torque converter and cooler lines.Click to see full answer. Keeping this in consideration, how long do transmissions last? approximately 7 years Also Know, how much does it cost to replace a transmission? Average Cost of Rebuild, Repair, and Replace: According to Transmission Repair Cost Guide readers, the average cost of transmission replacement ranges from $1800 to $3400. A used/salvage transmission ranges from $800 to $1500, a rebuilt transmission from $1100 to $2800 and a remanufactured from $1300 to $3400. Also to know is, how do I know if I need to replace my transmission? Here are a few warning signs that your car may be in need of transmission repair. Problems with shifting gears. Grinding or shimmying between gears. Unusual noises and “whines” Burnt, cloudy transmission fluid. Burning odor. Leaking transmission fluid. How long can you drive on a bad transmission?Driving on a bad transmission is never a good idea and you should not do it. Technically the vehicle can still be driven, but every time you do drive it you are risking your chances. If metal shavings begin to chip off and get into your coolant, you will have a much larger repair on your hands.