How to Change the Diff Fluid on a Honda Rancher 420

Changing the final drive and front diff oil on an ATV is an often overlooked maintenance task.  

A Honda Rancher 420 takes the same type of fluid on both ends, and you should change the differential fluid and the final drive fluid in your TRX420 once every two years, regardless of mileage. Watch the video above and follow the steps below to change the drive shaft oil on a Honda Rancher TRX420. 

Tools and Parts Needed – Honda TRX 420 Rancher Oil Change

Tools

  • 3/8th ratchet
  • 10mm, 12mm,17mm sockets
  • Torque wrench

 

Parts

  • Honda drive shaft oil 

 

NOTE: Two bottles of Honda drive shaft oil are needed to change both the front differential and final drive fluid.

Honda Rancher Front Differential Fluid Change

Step 1. Remove the top fill bolt (located on the right-hand side of the differential as you’re facing the ATV) with a 17mm socket. 

Honda Rancher 420 front diff fluid change

Step 2. Get a drain pan to catch the fluid, and remove the 10mm drain bolt located underneath the front differential.  

Honda TRX 420 front diff fluid change

Step 3. Replace the drain bolt once the fluid has completely drained, and tighten it to 9 foot-pounds.   

Honda Rancher front diff fluid change

Step 4. Pour Honda diff fluid into the fill bolt opening from Step 1. 

NOTE: It should take between 7.5 and 8 oz. of fluid, but you’ll know yours is full when the fluid starts to run out of the opening. 

Honda Rancher ATV front diff fluid change

Honda TRX 420 Rancher diff oil change

Step 5. Replace the fill bolt, and tighten it with your 17mm socket. 

NOTE: Don’t overtighten it. If you have a little excess fluid around the bolt when you’re done, clean it up with some contact cleaner.   

Honda Rancher TRX differential oil change

Honda Rancher Final Drive Fluid Change

Step 1. Remove the three 12mm bolts (one at the front and two at the back) underneath the drive housing that hold the skid plate in place, followed by the skid plate itself. 

Honda Rancher 420 final drive fluid change

Step 2. Remove the rear 17mm fill bolt on top of the housing.  

Honda Rancher ATV final drive fluid change

Step 3. Get a drain pan underneath, and remove the check bolt using a 10mm socket.  The check bolt is low on the left-hand side, facing the rear of the unit.

Honda TRX420 final drive fluid change

Honda Rancher 420 rear diff fluid change

Step 4. Clean around the drain bolt to remove any dirt or mud caked around it, and remove the drain bolt with a 10mm socket. The drain bolt is low and on the right-hand side. 

Honda TRX 420 ATV final drive oil change

Step 5. Replace the drain bolt once the fluid is finished draining, and use a torque wrench to tighten it to 9 foot-pounds.  

Honda TRX Rancher final drive oil change

Step 6. Fill the rear drive with Honda drive shaft oil. 

NOTE: It will only take about 2.5 oz., but you’ll know it’s full when fluid begins to run out of the check bolt opening on the bottom left of the housing.

Honda Rancher rear diff fluid change

Honda TRX 420 rear diff oil change

Step 7. Replace the check bolt, and torque it to 9 foot-pounds.  

Honda TRX Rancher 420 rear diff fluid change

Step 8. Replace the fill cap, and tighten it just enough.  

Honda Rancher ATV rear diff oil change

Step 9. Reattach the skid plate, tighten the three 12mm bolts that hold it in place and you’re done.  

Honda TRX 420 ATV rear differential fluid change

The steps to change the differential fluids on a Honda Rancher are the same or similar across the board for all models. However, if you want to see a slightly different take for another model, watch the video below to see how to change the rear differential oil on a Honda Rancher TRX 350

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