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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.

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Presentation Transcript
objectives
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
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
Plain Bearings
  • Example: engine crankshaft bearings
    • Do not use rolling parts
    • Provide sliding contact between two mating surfaces
    • Also called friction bearings
frictionless 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
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
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
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
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
  • 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
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 d1
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
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
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
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
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 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
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
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
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
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
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
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
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
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