How often you need to flush your transmission depends on the make and model, with specific recommendations available in your owner's manual. Generally, though, the service is necessary every couple of years on average. Your transmission is one of the vital systems on your car, and it depends on the fluid to stay well lubricated and working well. The following symptoms indicate it may be time to drain and clean the transmission fluid.
1. Grinding Gearbox
Odd grinding noises from the transmission gearbox are often one of the earlier signs of dirty transmission fluid. The noise will be most obvious when you are changing gears on a manual transmission, or when giving an automatic gas so that it is going through gears as you accelerate. If you hear grinding, schedule service right away before further damage occurs.
2. Sticking Gears
Being stuck in gear doesn't necessarily mean transmission failure is imminent, but it does mean you need to schedule a draining, flush, and servicing right away. When the gears stick due to dirty fluid, it may be almost impossible to shift the gears. With automatic transmissions, you may hear the engine rev loudly or acceleration may be slow because the transmission isn't shifting properly.
3. Vehicle Surging
Surging feels like the car is jumping forward. When dirty transmission fluid is the cause, you may not even notice a pattern to the surging, as it will seem to happen randomly. The surging is a result of a stuck gear finally engaging fully thanks to poor lubrication from dirty fluid. The gear eventually releases and the car surged forward with the gear change.
4. Gear Slippage
Restricted transmission fluid full from contaminants in the lines may make it difficult for the car to stay in gear even once it is put into gear. The gear knob for a manual transmission will physically pop out of place and put you back in neutral, for example. An automatic vehicle will rev loudly before losing speed as it drops back into the lower gear. The revving and hesitation is a sign that a transmission flush is necessary.
Sometimes the signs of dirty transmission fluid are more subtle. You may not hear a lot of noise, and the vehicle may not rev or show drastic surges. Instead, you may just notice a bit of hesitation upon acceleration, particularly around the normal speeds when your transmission typically shifts. The car may recover quickly from the hesitation, but you should still take it in for servicing.
Contact a mechanic for more information about automobile transmission fluid draining.