When it comes to the oil you put in your motorcycle it’s always smart to use exactly what the manufacturer recommends. For more information about the best engine oil to use, check out our article on oil changes.
On some bikes, the engine oil also lubricates your transmission and besides oil in your forks, it’s the only oil on your bike that you really need to change. The most common exception is bikes with a shaft drive where the rear differential requires lubrication as well. If this is the case, check your owner’s manual for how often you should change this fluid and what type to use.
More than likely your bike’s rear differential will require a hypoid gear oil here. Hypoid gear oil is nothing fancy but it is designed for a very specific application: lubricating hypoid gears. Hypoid gears are found in lots of axles and differentials where the gears are not parallel but also where the gears are slightly misaligned meaning the center of the shafts they ride on would not intersect if you continued an imaginary line out from the gear. The importance here is that hypoid gears have different loads and forces on them then the gears in your transmission which ride on parallel shafts. This unique alignment of the gears requires a special lubricant that can stand up to the pressures and temperatures in your bike’s gearbox. For these reasons, if your manufacturer specifies hypoid gear oil, it’s important to use it.
Like any oil-lubricated component the oil weight is also very important. The weight refers to the viscosity and too thick of an oil won’t lubricate everywhere and too thin of an oil won’t stand up to the forces and will cause poor lubrication when it gets hot.
Most oils today are multi-viscosity oils, like 75W-90 or 10W-40. This means that they change viscosity as the temperature changes. The goal here is to keep a more consistent viscosity over a wider temperature range. When it comes to differentials in shaft driven bikes this may not be as important as the temperatures may not be that extreme. It’s also possible that the manufacturer of your motorcycle designed it to use a single viscosity oil or “straight weight”. These types of oils are getting more and more difficult to find, but don’t worry! At PJ1 we’ve got your straight weight hypoid gear oil needs covered! If you’re doing an oil change in the differential of your shaft-driven bike, use PJ1 Hypoid Gear Oil! PJ1 Hypoid Gear oil is a straight 90 weight oil specially designed to lubricate the gears in your motorcycle differential. It will maintain it’s properties even at high shear and over long service intervals while meeting GL-4 and GL-5 standards. Pick up a bottle at one of our certified dealers.