Machinery Lubrication magazine published by Noria Corporation
Issue link: https://www.e-digitaleditions.com/i/1005929
52 | July - August 2018 | www . machinerylubrication.com BACK PAGE BASICS able to mix with the in-service grease. When in doubt or if there are compatibility concerns, try to perform as thorough of a grease changeout as possible. A utomot ive g re a s e s h ave performance specif ications that are similar to the gear designations of oils. ese specifications, which were originally classified by NLGI, follow a testing protocol outlined by ASTM International. e clas- sifications for automotive greases fall into two categories: chassis and wheel bearings. Some greases that pass both testing protocols may bear the dual-service mark. Chassis greases are classified as "LA" for light duty and "LB" for severe duty. Wheel bearing greases have three classifications: GA, GB and GC. Like the chassis classi- fications, the main difference is how robust the grease is and how severe the driving conditions are. ey range from mild duty (GA), to moderate duty (GB) and severe duty (GC). e regreasing frequen- cies follow the same pattern, with more frequent relubrication for GA to less frequent with GC. Most greases employed in automo- tive applications tend to hold the dual-service mark, which includes LB and GC. The GA-GC wheel bearing classifications have similar testing performed per the specification, but the protocol varies based on the classification. All wheel bearing classif ications are subjected to consistency, dropping point and low-temperat u re per forma nc e tests. ey also all have the same criteria for consistency, which puts them in the NLGI consistency range of 1-3. e most common grease consistency is NLGI 2. For the other two tests, the acceptance limits change according to the classification, with GC requiring higher values in most of the other tests. Additional testing for corro- sion protection, water resistance, leakage, high-temperature life, wear protection and elastomer compatibility is performed for GB and GC greases. e GC greases are tested for extreme-pressure performance as well. During installation, grease is often packed into these bearings by hand. Not only should grease be packed into the bearing, but some grease should be applied to the housing and on the wheel end's inside surfaces where the bearing sits. is will help prevent corrosion. e housing should also have some grease in the cavity surrounding the bearing, but it should not be filled. is space in the cavity will permit grease to be spun out of the bearing as well as provide room for thermal expansion of the lubricant. If the cavity is completely filled, grease churning and excessive heat will result. Certa in wheel ends have grease fittings that enable peri- odic regreasing of the bearing. If regreasing these with a grease gun, be sure to apply grease slowly and stop if abnormal back-pressure is experienced. Keep in mind that a grease gun can generate enough pressure to blow out seals and create an opening that will allow contam- inants to enter and oil to bleed out. Key Considerations W hen lubricated correctly, wheel ends should meet or exceed their estimated design life. e key items to consider include main- taining the oil level, regreasing at the proper frequency, using the right specification for oils and greases, and routinely monitoring the wheel assembly for any signs of leakage. If the seals are leaking and the lubricant is allowed to be flung out of the housing, it may reach the brakes, which could lead to a malfunction. Also, if lubricant is no longer present, the bearing may heat up and cause a fire. e wheel could even become unattached and result in damage or harm to other motorists. erefore, wheel ends should be properly maintained for the perfor- mance of the vehicle as well as the safety of the public. eir lubrica- tion doesn't need to be mysterious and can often be performed during normal maintenance of your vehicle. If you take your vehicle to a repair shop, be sure the principles outlined here are followed so you will be set for your next road trip. ML References ASTM D7450-13 Standard Specifica- tion for Performance of Rear Axle Gear Lubricants Intended for API Categor y GL-5 Service, ASTM International 2018 Annual Book of ASTM Standards ASTM D4950-14 Standard Classifi- cation and Specification for Automotive Ser vice Greases, ASTM International 2018 Annual Book of ASTM Standards Fitch, J.C., Scott, R., & Leugner, L. (2012). "The Practical Handbook of Machinery Lubrication - Fourth Edition." Pirro, D.M. & Wessol, A.A. (2001). "Lubrication Fundamentals - Second Edition, Revised and Expanded." About the Author Wes Cash is the director of technical services for Noria Corpora- tion. He serves as a senior technical consultant for Lubrication Program Development projects and as a senior instructor for Noria's Oil Analysis II and Machinery Lubrication I and II training courses. Wes holds a Machine Lubrication Technician (MLT) Level II certification and a Machine Lubricant Analyst (MLA) Level III certification through the International Council for Machinery Lubrication (ICML). Contact Wes at wcash@noria.com to learn how Noria can help you choose the right lubri- cants for your application .