Polaris Sportsman 850 Gearcase Fluids Change

Changing the transmission and diff fluids in a Polaris ATV is an important part of its routine maintenance schedule. Drive system fluids break down over time, causing greater wear on the precision parts of the drivetrain. 

Changing these fluids can prevent that from happening. Polaris recommends changing the drive system fluids after every 50-75 hours of use. Watch the video above and follow the steps below to change the transmission and diff fluid on a Polaris Sportsman 850 ATV.

Tools and Supplies - Polaris Sportsman Drive System Fluid Change

• 3/8th ratchet and extension
• 8mm Allen
• Pick tool
• Torque wrench
• Fluid pump

• 5/16 clear hose
• Polaris AGL gearcase lube (two bottles)
• Polaris Demand Drive fluid
• Polaris Angle Drive Fluid

Polaris Sportsman Front Gearcase Fluid Change

Step 1. Remove the 8mm Allen fill bolt for the transmission. See #23 in the front gearcase diagram for the Sportsman 850. 

NOTE: We removed the front wheel on our Sportsman so you can see the process, but it's not necessary to do this job.

Step 2. Get a drain pan to catch the fluid, and remove the 8mm Allen drain bolt located underneath the front differential. Check the fluid to make sure it's not milky, which is an indication of water in the transmission. Once the fluid has completely drained, replace the drain bolt. 

Step 3. Insert one end of the clear tube into the fill bolt opening, and attach the other to the hand pump. Use the hand pump to fill the gearcase with Demand Drive fluid.

NOTE: The tank holds about 10 oz., or roughly a third of the bottle. You'll know it's full when the fluid starts to run out of the opening. When it's full, replace the fill bolt. 

Active Descent Control Fluid Change

Step 1. Remove the front storage compartment. Next, flip up the two anchors located inside the compartment, then close the compartment back to make it easier to lift it straight off the nose of the unit. 

Step 2. Remove the plastic cover over the reservoir cap by taking off the two Torx head bolts and pulling the cover away.   

Step 3. Remove the reservoir cap and the rubber seal underneath it.

Step 4. Flush the system by first topping off the reservoir with Demand Drive fluid.    

Step 5. Locate the bleeder valve in the wheel well of the unit. There's one on either side, so you can choose which one you prefer. Remove the dust cap, then place a box-end-wrench over it and attach a length of clear hose. 

Step 6. Turn the wrench to the left to open the valve so the fluid will drain. 

NOTE: Keep adding fluid up at the reservoir during the draining so the system doesn't run dry. 

Step 7. Once you've flushed it and seen 4-5 ounces drain through the bleed valve, close the valve by turning it to the right. Next, replace the seal and the yellow cap at the top. 

Step 8. Replace the cover and its two Torx screws. Next, replace the cargo compartment and secure it by closing the two anchors inside.   

PRO TIP: Removing the skid plate can help make the following steps a little less messy. Check out our Polaris Sportsman 850 rear skid plate diagram to see how it's attached.

How to Change the Transmission Fluid on a Polaris ATV

Step 1. Find the drain bolt and fill bolt by looking at the transmission from right rear. Get a drain pan underneath the transmission and remove both bolts. 

NOTE: Make sure you get the Allen inserted completely into the head of the bolt, otherwise it could strip.  

Step 2. Clean off the magnet on the drain plug to capture any filings from inside the transmission, then replace it in the transmission housing. 

Step 3. Fill the transmission with Polaris AGL gearcase lube using the hand pump. It takes about 37 oz., so you'll need two bottles. You'll know it's full when fluid starts to run out of the opening.  

Step 4. Replace the fill plug and tighten it to 12-14 foot-pounds. Don't overtighten it.  

Polaris Sportsman Rear Diff Fluid Change

Step 1. Get a drain pan underneath, and remove the rear diff drain and fill plug bolts. Wait for the differential to completely drain. 

Step 2. Clean and replace the drain plug after the differential is finished draining. 

Step 3. Follow the same process you used to fill the transmission, but use Polaris Angle Drive fluid instead. Again, you'll know it's full when fluid begins to run out of the fill plug opening.   

Step 4. Replace the fill plug and you're done.