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© 2012 Delmar, Cengage Learning

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

– 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:

– 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

– 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


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


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

Documents

[PPT]Bearings, Seals, and Greases - Higher Ed eBooks & · Web viewTitle Bearings, Seals, and Greases Last modified by Rita Document presentation format On-screen Show (4:3) Other titles