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Bearings, Seals, and Greases

Bearings, Seals, and Greases

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Bearings, Seals, and Greases

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  1. Bearings, Seals, and Greases Chapter 60

  2. Objectives • Understand terms that relate to wheel bearings • Select the correct grease to use for a particular application • Describe the various wheel and axle bearing arrangements • Service wheel bearings on front and rear axles

  3. Introduction • Automobiles contain many types of bearings • This chapter deals with fundamentals of bearings, seals, and lubricants • Last part of chapter covers bearing service

  4. Plain Bearings • Example: engine crankshaft bearings • Do not use rolling parts • Provide sliding contact between two mating surfaces • Also called friction bearings

  5. Frictionless Bearings • Provide a rolling contact • Ball, roller, or needle bearings • Made of hardened steel alloys • Ground to a precise finish and size • Must be lubricated • Some are sealed • Ball or roller bearings • Balls or rollers ride between an inner race and an outer race • Bearing cage holds balls or rollers in position

  6. Bearing Loads • Bearings are made to handle different loads • Radial load: bearing load in up-and-down direction • Thrust load: load in front-to-rear direction • Also called axial thrust

  7. Ball Bearings • Ride in machined grooves • At rest: load is distributed equally wherever balls and races are in contact • Control end thrust and radial movement • Must control thrust: groove in bearing race will be offset to one side • Single-row bearings • Susceptible to damage when shaft is misaligned

  8. Roller Bearings • Used great load-carrying capacity is needed • Provide more surface area of contact with the race • Several types • Do not control end thrust • Most popular is the tapered roller bearing • Used for front-wheel bearings • Can control end thrust when installed with tapers facing in opposite directions • Needle bearing • Very small roller bearing

  9. Wheel Bearings • Found on all wheels of a vehicle • Axle bearings are on live axles • Drive axle bearings • Located at ends of rear axle housing on RWD car or on hub on FWD car • Full-floating axles • Found on ¾ ton and larger trucks and vans • FWD bearings • Compact and need to fit in a tight space

  10. Greases • Greases are used in: • Wheel bearings and chassis joints • Universal joints and gear boxes • Properties and characteristics of grease • Limited by quality of oil it is made of • Greases are fibrous • Different sizes of fibers available • Greases do not have a sharp melting point • Viscosity of oil used in making grease is important to grease's apparent viscosity

  11. Greases (cont'd.) • Automotive grease • Classified by NLGI • Grease types • Extreme pressure lubricants • Same as those found in gear lubricants • Chassis grease • Consistency allows application through zerk fitting • Wheel bearing grease • Resistant to heat

  12. Greases (cont'd.) • Universal joint grease • Made for universal joints • Multipurpose grease • Satisfies requirements of chassis, wheel bearing, and universal joint lubricants • Solid lubricant grease • Often used to lubricate speedometer cables, emergency brake cables, splines, and leaf springs

  13. Wheel Bearing Seals • Automobiles and equipment use seals to: • Seal in lubricants • Keep different lubricants separated • Keep out dirt • Maintain vacuum or pressure

  14. Seal Materials and Design • Most popular seals are made of synthetic materials • Most lip seals made of nitrile • Silicone seals • Often used in engines and transmissions • Fluoroelastomers • Used with special lubricants and chemicals • Non-synthetic seals • Leather, felt, etc.

  15. Seal Tolerance • Seals can accommodate shaft that is undersized up to 1/64” if parts are in perfect alignment • RMA recommends runout tolerance be held to ±0.003” for shafts up to four inches in diameter • Surface finish should be smooth

  16. Wheel Bearing Diagnosis and Service • Seal and bearing failure • Lubricant can leak out • Moisture can leak in • Boat trailer bearing failures • Common wheel bearing problem: trailer is towed for a long distance before launching • Possible solution: Bearing Buddy®

  17. Wheel Bearing Adjustment • Wheel bearings must be adjusted correctly • Designed to operate with very little clearance • Generic method of adjusting a loose bearing can be done with tire raised off ground • Spindle nuts are kept in place with a cotter pin • Remove to tighten • Washer under spindle nut has a tab that fits into spindle groove • Prevents bearing from loosening or tightening • Wheel bearing nuts are typically hexagonal

  18. Wheel Bearing Adjustment (cont’d.) • Selecting and installing a cotter pin • Use largest diameter cotter pin that will fit into hole • Pull longer end of cotter pin to seat fully in its hole • Cut it off • Cut off remaining end flush with spindle

  19. Disc Brake Caliper Removal • Procedure for repacking disc brake wheel bearings • Same as that followed for drum brakes • Except disc caliper must be removed in order to gain access to the inside wheel bearing • Caliper must be supported or wired to the steering knuckle support

  20. Repacking Wheel Bearings • Major steps and considerations • Remove hub and bearings from spindle • Seals are replaced during a bearing repack • Use a long dowel or drift to remove the seal • Clean out the old bearing • Look for metal flakes • Let the clean bearing air dry

  21. Bearing Inspection and Diagnosis • After cleaning inspect for damage • Spalling: pieces break off the bearing metal • Brinelling: bearing or race has indentations • Add grease to bearing • Pack with new grease by hand or pressure bearing packer • Put small amount of grease in cavity of hub • Inspect the spindle • Clean and lubricate

  22. Diagnosing Wheel Bearing Noise • Driving car can help pinpoint problem • Check tires and bearings • Make slow left and right turns • Shifts weight of vehicle from one side to the other • Weight increases on bearing: noise increases

  23. Replacing Bearing Races • Anti-friction bearings usually have one race that is pressed fit and the other is push fit • When a damaged wheel bearing is replaced: pressed-fit race must be removed • Old bearing race: removed by pounding it with a drift punch or special tool • New race must fit the hub tightly • New race can be chilled in refrigerator to make easier to install

  24. Servicing Front-Wheel-Drive Bearings • Most bearings on FWD vehicles are sealed • Require no service • Remove axle to get to bearing • Puller often required • Front-wheel bearing • Pressed or bolted onto the steering knuckle • Some manufacturers recommend bearing replacement any time FWD assembly is removed • Special care required during reassembly