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How to Flush a 4L80E

The transmission fluid is vital to the health of the transmission on the Chevrolet Silverado, Suburban, Tahoe, Van, Express, Avalanche, and the GMC Sierra, Yukon and Savana. These makes and models are all part of the 4L80-E transmission series designed by General Motors for longitudinal engines. This fluid provides the hydraulic power necessary for the transmission to engage and disengage, provides lubrication to the gears, and lowers the operating temperature of the unit.

Your transmission fluid needs to be replaced at regular intervals just as you replace your oil at regular intervals. While it is not replaced as often as your oil, it is still imperative that you keep clean fluid running through your transmission to avoid damage to the moving parts.

While you can take your Chevrolet or GMC to the dealership in order to have the fluid changed, you may find that it is less expensive and not that hard to do the fluid change yourself.

Here are the instructions for changing the transmission fluids on a 4L80-E transmission.

Tools Needed:

  • Hose clamps
  • 3/8-inch clear tubing
  • 3/8-inch brass transmission cooler line fitting
  • Adjustable wrench
  • 5/8-inch crescent wrench
  • Catch pan
  • 15 quarts of ATF

Before you start, place your vehicle on a solid, flat surface and wear any safety equipment needed for the procedure. Goggles will protect your eyes from splashing fluids, and gloves will keep your hands clean.

Transmission Fluid Removal

  1. Place the catch pan on the driver’s side of the vehicle in order to monitor the flushing of the fluid.
  2. Find the upper transmission line. It is on the passenger side. Remove it from the radiator. There is a black plastic bracket that you need to pull back, but be careful because it is shielding an e-clip that you do not want to remove. A wrench is necessary to loosen this fitting.
  3. After you have the line removed, you will connect the brass transmission cooler line fitting and the clear tubing. Secure it so there are no leaks.
  4. Place the end of the tube into your catch pan and secure it.
  5. Start your engine. You will see the fluid begin pumping into the catch pan. Watch this closely because as soon as you see any bubbles or hear any bubbling sounds, you need to shut off the vehicle immediately. It only takes about 30 seconds for three or four quarts of fluid to leave the vehicle.
  6. Add three or four more quarts of new fluid to the transmission by pouring it into the transmission dipstick tube. Add it until you see that it reads FULL.
  7. Start the engine again and repeat the above steps. You will do this refill and repeat three times as you watch the transmission fluid change colors. It will go from the dark color of a dirty fluid to a red color that is clean. As soon as you see the fluid running red, you know that you have fully flushed out the system.

Refilling the Transmission Fluid

  1. As soon as you have flushed the fluid, you will reconnect the transmission line after you remove the brass fitting and clear tubing.
  2. Add new, clean transmission fluid through the transmission dipstick tube until the dipstick reads “Full Cold”.
  3. Start your engine and let the transmission warm up.
  4. After you have reached operating temperature, look at the dipstick again and add more fluid if needed to reach the right level.

That is all you need to change out the transmission fluid in your 4L80-E transmission vehicle.

NOTE: Please discard your waste transmission fluid in an environmentally responsible manner. Save the penguins! :)