The transmission is one of the most important parts of your vehicle. Without a good transmission, your car will not operate at all, and you will be left with a large, immobile piece of metal yard art. There are several things you may notice if your transmission is beginning to have problems. If you notice your car having transmission issues, you should take it to a repair shop immediately to avoid further damage.
Not engaging properly
If you put your car in gear and it does not go right away, there is a good chance that your car is having transmission problems. Your car should shift from gear to gear quickly and easily with minimal resistance. If your engine is revving to a high rpm and not shifting into another gear, your transmission may need to be serviced.
Noises
If you put your car in gear and a moment later it shifts with a clunk that makes the whole car shake, your transmission needs to be serviced or repaired. Your transmission should not be making any clunking, grinding or whining noises while you are driving your car or shifting. If you can hear your transmission, chances are you have a problem.
Fluid problems
Check your car’s transmission fluid. If the fluid is low, nonexistent or has turned a strange colour, your transmission is having some sort of problem. Transmission fluid leaks can cause your transmission to overheat and burn up. The colour of your transmission fluid should be a translucent dark pink or red. If it is brown, milky or smells burnt, you need to have your transmission looked at by a professional.
Signs of transmission trouble
The transmission is a key component of an automobile. It is also a very expensive one to replace. If you pay attention, there are many warning signs that the transmission is failing and needs attention. Taking care of problems early on can be the difference between repairing the transmission and replacing it.
Fluid leaks
Any sign of leaking transmission fluid is a sign of trouble. The larger the leak, the more urgent it is to have the transmission inspected by a mechanic. Look for a red-coloured liquid.
Low transmission fluid
If the transmission is not leaking–yet the fluid continues to run low–that’s a sign the transmission is overheating and burning fluid.
Slipping
The transmission will slip while in gear, or while shifting, meaning the car does not shift firmly and quickly as it normally should. Instead it shifts slowly, with the engine revving and a temporary lack of acceleration.
Metal shavings in fluid
If the transmission fluid has metal shavings in it, the transmission is severely damaged and will need to be replaced.
Hard shifting
A failing transmission may give the car a hard, jerky action when shifting in between gears.
Source: ehow.com