Machinery Lubrication

Machinery Lubrication July - August 2018

Machinery Lubrication magazine published by Noria Corporation

Issue link:

Contents of this Issue


Page 55 of 76

www . | July - August 2018 | 51 ML when compared to grease lubrication. e oil is applied either directly to the hub via a fill port or supplied inter- nally from the differential utilizing a piping mechanism. In both cases, maintaining the correct oil level and selecting the appropriate oil are key to preserving the bearing and ensuring that the hub functions properly. Bearings that share oil from the differential will commonly be lubricated with gear oil. Even hubs that are splash lubricated in their own individual bath may be lubricated with an approved gear oil. W hile most people may be familiar with gear oils, the ones used in automotive applications are slightly different than those for industrial applications, which have their own designations and viscosity grade systems. Gear oils for these applications should meet the specifications of the American Petroleum Institute (API). For drive wheel ends, where the oil is shared between the hub and the axle, this becomes very important, as the oil will be lubricating a gear set as well as a bearing set. Be sure to consult the original equipment manufacturer's recom- mendations to see which gear oil designation is preferred. e most current and widely used is GL-5. is designation is employed with most hypoid gear sets and has stan- dard performance levels listed in the ASTM D7450 specification. Much of this specification is dedicated to testing the lubricant's ability to reduce wear on gear components. Other tested parameters include foam stability, rust protection, and thermal and oxidative stability. e full range of gear oil desig- nations span from GL-1 through GL-6. e only active designations are GL-4 and GL-5. GL-4 is utilized in many manual transmissions and transaxles. ese tend to be used more at lower speeds and loads when compared to GL-5. e other designations are considered inactive and usually are not recommended in these applications. Breaking the mold is the MT-1 designation, which is frequently employed in non-syn- chronized manual transmissions. These oils are more specialized, and care should be taken to prevent accidentally mixing these with other fluids. In order for a lubricant to meet these specifications, there must be a healthy dose of additives to fortify the base oil. The most common additives in these types of fluids are antioxidants, viscosity index improvers and extreme-pressure (EP) additives. Some EP additives contain active sulfur phosphorus, which can be corrosive to softer metals, so always check your equip- ment manual before selecting and using any oil for your particular application. In addition to the oil designa- tion, you must also choose the proper oil viscosity to replace or refill the system. e viscosity will be denoted by the SAE viscosity grade and typi- cally will be listed in the same place as the oil designation. Many auto- motive applications utilize a 75W-90 viscosity oil in these applications, but it is not uncommon to find some viscosities higher than SAE 140. e higher viscosities are often used for higher loads and higher torque applications or for those experiencing higher temperatures. Oil Levels W hen using oil to lubricate a wheel end, the oil level will be critical to the system's health and overall performance. If the wheel end has its own individual reser- voir, there likely will be a sight glass which can be used to monitor the oil level. Depending on the type of wheel end, the oil level can vary, so be sure to check the sight glass for the "full" mark and not simply look for signs of oil in the glass. For wheel ends that share a sump with the rest of the axle assembly, you may need to pull the level plug from the differential or gear assembly to verify that the oil is at the appro- priate operating level. Ideally, you should check these levels when the vehicle is on level ground, as the slope of the surface could impact the oil level and give you a false reading. Remember, having too high of an oil level can be just as dangerous and destructive as having an oil level that is too low. Grease Lubrication e vast majority of wheel ends are grease lubricated. Unlike oil, grease does a better job of staying in place within the bearing and housing. It also can resist breaking down while in service better than a traditional oil. e downside is that grease can be difficult to replace, and overgreasing is common in many applications. Passenger-car wheel bearings are typically grease lubricated and sealed for life, which means the lubricant can't be replaced. Not only must the in-service grease provide the same lubricating properties as oil, but it also must be able to resist the temperatures present in the wheel end to avoid excessive bleeding of oil from the thickener. is is very important in applications that require frequent braking, as the fric- tion in the brakes is often transferred into the wheel bearings. When selecting a grease for a wheel bearing, start by considering the recommended lubricant or the grease that is already in use within the bearing. Greases are known to have compatibility issues when different types are mixed. is risk is greatly minimized if you can fully replace the grease charge by cleaning out all remnants of the old lubricant. Some research into the grease's thickener and base oil can shed light on whether the new grease will be 61% of lubrication professionals consider wheel-end lubrication during normal maintenance of their vehicles, according to a recent survey at

Articles in this issue

Links on this page

Archives of this issue

view archives of Machinery Lubrication - Machinery Lubrication July - August 2018