Question: how do you know if your transmission needs to be flushed?
Answer: Transmission Grinding or Strange Noises. If you are wondering if your transmission is contaminated with dirt, sludge, and grease you will notice that it will show symptoms similar to inadequate levels of transmission fluid. ... 
Problems Shifting Gears. ... 
Slipping Gears. ... 
Surging Of The Vehicle. ... 
Delay in Movement.