© 2012 delmar, cengage learning bearings, seals, and greases chapter 60
TRANSCRIPT
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© 2012 Delmar, Cengage Learning
Bearings, Seals, and Greases
Chapter 60
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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
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Introduction• Automobiles contain many types of bearings
– This chapter deals with fundamentals of bearings, seals, and lubricants
– Last part of chapter covers bearing service
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Plain Bearings• Example: engine crankshaft bearings
– Do not use rolling parts
– Provide sliding contact between two mating surfaces
– Also called friction bearings
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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
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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
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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
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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
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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
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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
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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
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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
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Wheel Bearing Seals• Automobiles and
equipment use seals to:– Seal in lubricants
– Keep different lubricants separated
– Keep out dirt
– Maintain vacuum or pressure
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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.
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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
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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®
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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
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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
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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
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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
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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
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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
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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
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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