How To Check & Replace You're Gearbox Fluids
Automatic Transmission/Transaxle Fluid Check:
The automatic transmission fluid should be checked with your cars engine running. The transmission dipstick is typically located behind the oil dipstick, and doesn't stick up quite as high. If you have trouble locating it, consult your owner's manual or call a dealership. Often, it will have the same colorful markings (yellow, red, etc.) as the oil dipstick so is reasonably easy to identify.
Start the engine and locate the transmission fluid dipstick. Before you do, though, make sure to remove anything loose hanging from your neck, such as long jewelry and tie back your hair if it is long. These could get caught in a running fan belt and cause you to have a potentially nastly accident.
With the engine running, extract the transmission dipstick. Wipe it clean and reinsert it, then extract it again. It will have similar markings to the oil dipstick, one mark for too low, another for too high.
Note: Transmission fluid will almost never be low. The automatic transmission / transaxle is a sealed system, requiring little maintenance. If your fluid is low, it most likely means you have a leak in the system, such as a worn seal or a crack somewhere and will need to see a mechanic.
Even if the level is OK, note the color and consistency of the fluid. If it is very dark or black, check your records and owner's manual and plan on getting it changed; it's probably overdue. Your fluid should be a nice pink.
Automatic Transmission/Transaxle Fluid Replace:
Unfortunately, unless you have a machine known as a "T-Tech" (in which case, you already know how to use it), you will need to take your vehicle to a mechanic in order to replace your Automatic Transmission fluid.
Manual Transmission Fluid Check:
This is done with the engine off. For most cars, you have to get under the car and remove the fill plug with a wrench. Stick your finger in and feel for fluid. If you can feel fluid on the tip of your finger, it's probably OK. Again, as above, note the color of the fluid and consult your owner's manual for exact procedures and service interval.
Manual Transmission Fluid Replace:
Place an Oil Catch Pan underneath your Tranny Drain Plug. Open the Tranny Fill Plug in order to allow fluid to evacuate faster and easier.
Slowly remove the Tranny Drain Plug and allow all fluid to drain.
Once complete replace the Tranny Drain Plug and fill transmission with manufacturers recommended fluid until it starts coming out of the fill plug hole.
Take any old fluid to your local quick lube to properly dispose of old fluid. This also gives you the opportunity to check your work for leaks.