i have grease coming out of the vent ,and it filled it up ...what do i do??If you have water / mud inside, it needs to be split like mentioned above. If not, you can just drain the oil, remove vent hose, take fill cap and drill and tap a grease zert. Lift bike off the ground so tires can be rotated. While pumping grease, slowly rotate the tires as you pump the grease into the differential. First you will see grease begin to push air and oil out of the bottom drain hole. Once you start getting pure grease out of drain hole, put plug back in. Keep pumping until grease starts coming out of vent tube on top of differential. Keep pumping until all air is pushed out and differential is completely packed with grease. Tighten plugs and put vent hose back on and ride around the yard for 15 mins or so. Remove vent hose and pump some more grease. If you get pure grease with no air coming out of vent, your good to go. If you still have air, keep pumping until all air is pushed out.