If your vehicle sticks when you try to change gears, or seems to be stuck in neutral, these are usually signs that you need a new transmission, or at least some major repairs for the gears and other transmission parts. However, there can also be other things wrong under the hood that might affect how the car shifts and performs when you change gears. Note a few of those problems here; this can help you know what to discuss with your mechanic and what to expect by way of repairs.
Slow pickup; hesitation
When you give your car gas, it should accelerate smoothly. While some cars may not have the fastest pickup simply because the engine is small, if you notice that there is suddenly hesitation from the vehicle, or no pickup at all, this can mean that the transmission is not engaging as it should and may be causing drag.
However, this can also mean there is a problem with the vehicle's exhaust system. When the car is idling, a clogged catalytic converter, holes in the tailpipe, and other such damage can allow oxygen to build up in the engine. In turn, the engine can't create proper combustion when you give it gas, and it hesitates. If the car's exhaust system is covered in rust, this is often a telltale sign that it's old and damaged, so have that system checked along with the transmission when your vehicle doesn't have proper pickup and acceleration.
Jumping or surging
When a transmission is failing, a vehicle may jump or surge forward after you change gears. This is often caused by worn teeth in the gears; the car jumps forward when those teeth finally line up, causing that sudden surge.
While a worn transmission is often the culprit for this surge or jump, this can also be the fault of the brakes. If the brake pads continue to squeeze the rotors even after you let your foot off the brake pedal, the car will surge or jump forward once they release. This late squeezing might be caused by bent or broken callipers, which push the pads against the rotors. It can also be the fault of worn pads that have slipped out of place, so that they continue to stick to the rotors after you release the brake pedal. If the transmission is fine, have your mechanic inspect the brakes for worn or broken pieces that would cause the car to hesitate and then suddenly jump or surge forward.
For more information on transmission and gearbox repair, contact a local mechanic.