Fluid Color and Quality | The color and quality of your transmission fluid is a good indicator of transmission health. Transmission fluid is often red (although it does come in other colors) and tends to get darker as it deteriorates. A burnt odor coming from the fluid or dirt and debris in the fluid are also indications that it's time for a transmission flush.
Grinding or Whining Noises | Strange noises indicate either low fluid levels or the need for a flush. If you notice grinding or whining noises, pull over and check the fluid level while the engine is running. If the level is acceptable, it may be time for a transmission flush.
Problems Shifting Gears | If your vehicle changes gears too quickly or too late while driving, or if your manual vehicle is hardly changing gears at all, it's likely an indication that the transmission has too much built up dirt and sludge to properly shift and needs a flush.
Slipping Gears | A buildup of dirt and contaminates may results in the loss of hydraulic power. Sludge and grime prevents the transmission from creating enough pressure to stay in the appropriate gear.
Surge or Delay in Movement | If your vehicle stalls for a few seconds after you put it in gear, it could be an indication of contaminated transmission fluid. If your car is quick to respond, a flush could help.