1. Gather your tools and materials.
You will need a new oil filter (Honda part number 15410-HM5-A01), a new crush washer (Honda part number 94109-14000), a funnel, a 17mm wrench, and a drain pan.
2. Prepare the quad.
Park the quad on a level surface and turn off the engine. Allow the engine to cool down completely before proceeding.
3. Locate the drain plug.
The drain plug is located on the bottom of the transmission case. It is a 17mm bolt.
4. Place the drain pan under the drain plug.
Make sure the pan is large enough to catch all of the fluid that will drain out.
5. Loosen the drain plug.
Use the 17mm wrench to loosen the drain plug. Be careful not to drop the bolt into the oil pan.
6. Allow the fluid to drain.
The fluid will drain out of the transmission case into the drain pan. Allow it to drain completely before proceeding.
7. Replace the crush washer.
The crush washer is located on the drain plug. Remove the old crush washer and replace it with a new one.
8. Reinstall the drain plug.
Reinstall the drain plug and tighten it until it is snug. Do not overtighten the drain plug.
9. Locate the oil fill plug.
The oil fill plug is located on the top of the transmission case. It is a 17mm bolt.
10. Remove the oil fill plug.
Use the 17mm wrench to loosen the oil fill plug.
11. Add new fluid.
Use a funnel to add new fluid to the transmission case. Add the amount of fluid specified in the owner's manual for your quad.
12. Replace the oil fill plug.
Reinstall the oil fill plug and tighten it until it is snug. Do not overtighten the oil fill plug.
13. Start the quad.
Start the quad and let it run for a few minutes to circulate the new fluid.
That's it! You have successfully changed the transmission fluid on your Honda 400ex quad.
