How to Clean a Transmission

Your vehicle’s transmission plays a crucial role in keeping your car running smoothly, whether it’s automatic or manual. Over time, dirt, grime, and transmission fluid residue can build up, reducing performance and even leading to overheating or premature wear. Cleaning your transmission—both inside and out—is an important part of vehicle maintenance that can help extend the life of your car.


Why Clean Your Transmission?

Before we get into the step-by-step process, let’s look at why cleaning your transmission is important:

  • Prevents overheating: A dirty transmission can trap heat, which may lead to breakdowns.
  • Improves performance: Clean transmissions shift more smoothly and operate efficiently.
  • Detects early signs of trouble: Cleaning allows you to inspect for leaks, cracks, or worn parts.
  • Prolongs lifespan: Removing grime and old fluid can help prevent damage over time.


Types of Transmission Cleaning

There are two main ways to clean a transmission:

  1. External Cleaning – Removing dirt, oil, and debris from the outside of the transmission housing.
  2. Internal Cleaning (Flush) – Replacing old, dirty transmission fluid with fresh fluid and cleaning the internal components.

We’ll go over both.


Tools and Materials Needed

Here’s what you’ll need:

For external cleaning:

  • Degreaser or transmission-safe cleaner
  • Nylon brush or toothbrush
  • Rags or microfiber towels
  • Safety gloves and eye protection
  • Jack and jack stands (if needed)
  • Garden hose or pressure washer (optional)

For internal cleaning (flush):

  • New transmission fluid (check your owner's manual for the correct type)
  • Transmission filter (if required)
  • Drain pan
  • Funnel
  • Ratchet and socket set
  • Transmission flush kit (optional for advanced DIYers)


How to Clean the Outside of Your Transmission

This is the easier and less technical process and can be done as part of regular maintenance.

Step 1: Safety First

  • Park your vehicle on a flat surface.
  • Turn off the engine and let it cool completely.
  • Wear gloves and protective eyewear.

Step 2: Raise the Vehicle (If Needed)

  • Use a jack and jack stands to safely lift the vehicle if you need better access underneath.
  • Always use jack stands for safety—never rely solely on a jack.

Step 3: Apply Degreaser

  • Spray a transmission-safe degreaser or all-purpose automotive cleaner directly on the transmission case.
  • Let it sit for 10–15 minutes to break down grime and oil.

Step 4: Scrub the Surface

  • Use a nylon brush or old toothbrush to scrub around seals, bolts, and hard-to-reach areas.
  • Focus on areas with heavy buildup or residue.

Step 5: Rinse and Dry

  • Use a garden hose or low-pressure washer to rinse the area (avoid using high-pressure water near sensors or wiring).
  • Dry with clean rags or let air-dry before starting the car again.


How to Clean the Inside of a Transmission (Fluid Flush)

Cleaning the inside of your transmission requires replacing the old fluid and filter (if applicable). Here’s how to do it safely:

Step 1: Gather the Right Fluid and Filter

  • Make sure you have the correct transmission fluid for your vehicle. Using the wrong type can cause serious damage.

Step 2: Warm Up the Engine

  • Run the engine for a few minutes to warm the fluid. This helps it drain more thoroughly.

Step 3: Drain the Old Fluid

  • Place a drain pan under the transmission.
  • Remove the transmission drain plug (if available) or unbolt the pan carefully.
  • Let all the fluid drain. This may take 10–15 minutes.

Step 4: Replace the Filter

  • If your transmission has a serviceable filter, remove the old one and install the new filter according to the manufacturer’s instructions.

Step 5: Clean the Transmission Pan

  • Wipe out the transmission pan with a clean rag.
  • Remove any sludge or metal shavings (these may indicate wear).
  • Reinstall the pan with a new gasket if required.

Step 6: Refill with Fresh Fluid

  • Use a funnel to slowly pour the new transmission fluid into the dipstick tube or fill port.
  • Add the recommended amount—typically between 4 to 12 quarts depending on the vehicle.

Step 7: Check the Fluid Level

  • Start the car and let it run for a few minutes.
  • Cycle through all the gears.
  • Check the transmission fluid level with the dipstick and add more if needed.


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