Bearings, Seals, and Greases Chapter 60

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

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

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

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

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

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

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

Wheel Bearings Found on all wheels of a vehicle Drive axle bearings 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

Greases Greases are used in: Properties and characteristics of grease 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

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

Greases (cont'd.) Universal joint grease Multipurpose 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

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

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.

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

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®

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

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

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

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

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

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

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

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