Most cars, whether automatic or manual, use transmission fluid in their transmission case. This fluid acts as a lubricant that allows the gears to shift easily. Cars with hydraulic braking systems also require fluid to apply pressure to the brakes. Both fluids should be checked monthly to make sure they are at proper levels.
Although these fluids should be checked monthly, they generally only need to be changed or replaced every 30,000 miles. However, leaks may develop or unusual friction may eat away at some fluid, causing them to wear away faster.
The levels of both brake and transmission fluid should be check monthly. However, in many cars, indicator lights will come on when brake fluid is low; some cars also check transmission levels. If either of these lights come on, check the fluid levels immediately.
