2 Function of wheel bearings Provides a low friction bearing surface for wheel rotation.Supports the weight of the vehicle.Transfers the lateral loads of cornering from the wheel and tire - into the body / frame.Lasts indefinitely - normally the life of the vehicle.
3 Radial loads acting on bearings Vehicle WeightRadial loads are forces acting on the bearings at a right angle to the axis of rotation.The weight of the vehicle is largest radial load.Jounce and rebound forces are applied to the bearing when the vehicle encounters bumps in the road.When the vehicle accelerates or the brakes are applied additional radial forces act upon the bearing.TractionBrakingJounce and Rebound
4 Axial forces acting on bearings Axial loads are loads that a parallel with the wheels axis of rotation.Cornering force is an axial loads.When the tires hit curbs or strike potholes sidewise high axial loads are applied to the wheel bearings.CorneringCurbs and Potholes
5 Anti-friction bearings Bearings that use rollers, balls or needles, riding between two races are considered anti-friction or low friction bearings.A rolling element, either a sphere, cylinder or tapered pin rolls along the surface of the races, reducing to a minimum the friction between the moving parts.A cage is sometimes used to separate the rolling elements.Anti-friction bearings are lightly lubricated by oil or light grease and do not require a force fed oil supply system like engine bearings.Some bearings are permanently lubricated and sealed at the factory - and require no maintenance whatsoever.Outer RaceInner RaceRolling Element
6 Bearing types Ball bearings Straight roller bearings Tapered roller bearingsNeedle bearings – not used as a wheel bearing
7 Ball bearingsBall bearings are suitable for light radial loads and very light axial loadsComponent parts:An inner race - with an external grooveAn outer race - with an internal grooveA set of ballsA stamped sheet metal or plastic cage
8 Dual row ball bearingsDual row ball bearings are one of the most common types of front wheel drive wheel bearingsWhen 2 ball bearings are placed side to side the ability of the combined bearings to handle axial loads is greatly increased
9 Dual row ball bearingsOuter raceOn most FWD cars a single outer race housing will have two grooves - for inboard and outboard ball racesTypically there will be two inner half/races - the external groove is machined for 1/2 the width of the ballsA single, plastic cage holds the balls in their proper position and helps to retain greaseOutboard inner raceInboard inner race
10 Sealed ball bearingsWheel bearing applications that utilize ball bearings are permanently sealed by 2 rubber disks installed in a groove in the outer race.These seals keep the grease from leaking out.They also keep dirt from getting into the bearing.This type of bearing should never be washed in solvent.There is no way to repack this type of bearing. If the grease has been washed away by solvent the bearing must be replaced.
11 Interference fitShaft and bearing are machined for a slight interference fitShaft is typically inch larger than the hole in the center of the inner raceWhen a force of a ton or more is exerted on the shaft the metal of the bearing will expand slightly to allow the bearing to be pressed onto the shaftIn some cases the outer race is a press fit into the housing that supports itThis will help to prevent the bearing from rotating inside the housing
12 Ball bearings for FWD vehicles FWD vehicles normally use a dual-row ball bearings for the front wheels.Some manufactures used two separate ball bearings mounted back to back.Since these are asymmetrical they must be mounted in proper orientation.Ball bearings used for FWD cars are lubricated and sealed at the factory and cannot be cleaned and lubricated in the field.
13 Cylindrical [straight] roller bearings The rollers have the same from one end of the roller to the other.Normally lubricated by oil - but can also be lubricated with light grease.Has very high radial load capacity - but very little axial load capacity
14 Cylindrical roller bearings Typically used for a rear wheel bearing on rear drive carsSince these bearings have very little axial load capability the axle shafts must be retained in the axle housing by horseshoe clips that fit into grooves machined onto the ends of the axle shaftsWithout these clips the axle shaft will literally slide out of the axle housingNo inner race required - the axle shaft is machined and hardened to allow the rollers to ride directly on the shaft
15 Tapered roller bearings Similar to a conventional [straight] roller bearing except thatRollers have a smaller diameter at one end than at the otherInner race is cone shaped - with lips at both ends to retain the rollersSheet metal cage positions and retains rollers onto the inner raceOuter race has an internal cone [cupped] shapeOuter race is not retained to the rest of the bearing assembly
16 Tapered roller bearings Have both a high axial and radial load capacity [heavy duty]Tapered roller bearings have the highest axial load capacity of all bearing typesUsed in heavy duty applications where axial load is high - such as rear axle pinion bearingsBest design for front wheel bearing
17 Disadvantages of tapered roller bearings Increased surface contact area adds strength but also adds drag - reduces fuel efficiencyTapered roller bearings must be periodically adjusted for preloadMinor wear in the races and rollers allow the bearing to loosen up - permitting looseness or wobble in the wheel assemblyAn adjustment nut, retained by a cotter pin is typically used for the preload adjustmentFront wheel drive vehicles rarely use tapered roller bearings because of thisAdded weight and complexity of an adjustment nut assembly is prohibitive in most FWD applicationsFour wheel drive vehicles generally have large and heavy steering knuckles [kingpins]Additional weight and complexity is generally not a concern
18 Wheel bearings for RWD cars RWD vehicles use 2 tapered roller bearings for each front wheelThe inboard bearing is larger and carries most of the weight of the vehicleThe outboard bearing is smaller and carries most of the outward thrust in corneringThe offset of the rim and tire places the center of the rim nearly directly over the inboard wheel bearing
20 Lubrication and Sealing The bearings are lubricated by wheel bearing greaseA lip seal is placed inboard of the inner wheel bearing to retain grease and keep dirt outA garter spring is used to maintain a slight pressure between the lip seal and the seal surface on the spindleA metal dust cap [ grease cap ] prevents grease from leaking to the outside
21 Wheel SpindleThe steering knuckle has a spindle [ tapered shaft ] to support the wheel bearingsTwo machined surfaces on the spindle support the bearingsA third machined surface is used for the lip sealThreads on the outboard end are cut for the preload adjusting nutThe outboard end of the spindle is usually drilled through to accommodate a cotter pinSeal surfaceInner bearing surfaceOuter bearing surface
22 Bearing retentionCastle nuts and cotter pins are normally used to retain the bearingsSome foreign cars use a split nut with an Allen bolt clampMany Japanese cars use a special lock nut - and a square cut groove in the spindleAfter the preload has been adjusted the soft metal lip on the end of the nut is hammered into the groove in the spindle with a hammer and chiselThis type of nut can only be used once
23 Bearing retentionInner race of the wheel bearings fit loosely over the spindleAlthough it is not desirable to have the inner races rotate on the spindle there is very little rotation that normally takes placeIf the wheel bearing fails however, the spindle may be damaged by the constant rotation of the inner race
24 Bearing retentionOuter races [ cups ] are pressed or hammered into the wheel hubOften the hub is integral with the front brake rotorsOn drum brakes the hub is usually retained to the drums by in interference fit between the wheel studs, brake drum and hub
26 Unit type – Bearing and Hub assembly Many FWD wheel vehicles have unitized bearings wheel bearings and hub assemblies that can be simply unbolted from the steering knuckleThese bearings and hubs often include the wheel flange and wheel studs.The bearing/hub assembly is normally attached to the steering knuckle by 3 large boltsThe ABS wheel speed sensor is often built into the bearing assembly.
27 Separate hub and bearing The wheel bearing is pressed into a bore machined in the steering knuckle and retained by very large snap rings
28 Separate bearing and hub When a wheel bearing needs to be replaced, the steering knuckle will need to be removed from the vehicle.A 10 ton press is typically used to press the hub out of the bearing and also to press the bearing out of the knuckleRemoval of the wheel bearings is a two part operationFirst the hub and hub flange must be pressed out of the wheel bearingOnce the hub and flange have been removed the snaprings can be removed from the steering knuckle and the bearing pressed out
29 Separate bearing and hub In some instances the hub and wheel bearing can be removed a slide hammerIn other cases special factor tools may be required for safe removal and replacement of the wheel bearings
30 Tapered Roller Bearings RemovalWith the wheel is removed the dust cap, cotter pin and preload adjusting nut can be removedThe thrust washer and outer wheel bearing can now be removedTo remove the inner wheel bearing the lip seal must be removed first
31 Grease sealsThe grease seals should always be replaced when servicing wheel bearingsIf new lip seals are not available the seal can be removed by reinstalling the rotor , without the outer bearingThread the adjusting nut back onto the spindlePull the rotor outward - while applying downward force at the same timeThe rotor will come free from the spindle - leaving the bearing, seal and nut on the spindleCaution ! - if care is not used in this procedure the wheel bearing may be ruined
32 If new lip seals are to be installed Remove the old lip seals with a seal puller once the rotor / drum has been removed
33 Inspection The wheel bearings can be cleaned using safety kleen Lightly polished bearing surfaces [ satin ] is normal on any bearing with a few thousand miles or more of wear
34 Examine the wheel bearings for: Spauling - large pits or chunks on the surface of the bearingGenerally caused by fatigue and high mileageBrinelling - imprint of parallel lines on the bearing surfaceCaused by impact loading or vibration while the wheels are not turning - as when it is transported on a flat bed truckGauling - surface of the bearing appears as though flakes of bearing material have pealed offCaused by overheating and / or insufficient lubrication [ or wrong lubricant ]Scuffing [ abrasive wear ]Scratches and pitting on the bearing surfacesCaused by abrasive material in the lubricantSmearing - polished edge near the outside edge of the bearingCaused by the bearing cup rotating in the hub boreRepair necessitates replacement of both the bearing and hub [ rotor ]Bent cage - dents or distortion in the bearing cageCaused by mishandling during assembly
36 Replacement As a rule wheel bearings are generally replaced in sets If there are any signs of damage to the bearing the entire bearing assembly must be replaced [ inner and outer races ]The outer race can be removed by hammering it out of the hub with a long tapered drift [punch] – a small brass drift is preferableMost hubs have two cast slots in the bore to facilitate bearing removalWipe all of the grease out of the bore to find themA special bearing installer tool is used to press or hammer the new bearings into the hub
37 Packing the bearing with grease With the new inner bearings repacked with grease the hub is reinstalled onto the spindleTapered roller bearings can be repacked by hand by scooping up a few ounces of grease in one hand and dragging the open end of bearing cage through the grease until you see grease oozing out of the openings between the rollers and the cage
38 Packing the bearing with grease A less messy way of packing bearings is by way of a packing tool that forces grease through the cageBearing packers force grease to fill the voids between the rollers and between the cage and rollers
39 Wheel bearing greaseWheel bearing grease is a specialized lubricant that is designed to stay solid at relative high temperaturesWheel bearing grease is sold in one pound plastic tubs that look like margarine containersChassis grease is not recommended for wheel bearings – it is normally sold in cardboard tubes that fit in grease gunsWhenever repacking wheel bearings always thoroughly clean the bearings and hubs to remove the old greaseIntermixing greases from two different manufactures may produce a chemical reaction between the two greases that either turns the grease to a very thin oil [ that will leak out ] or may reduce the greases ability to prevent friction between metal parts
43 Pre-torquing after bearing replacement. Many manufactures recommend a bearing pre-torquing procedureThe bearing is initially pretorqued to a very high level - let’s say 60 lbs/ftIt is then loosened and then properly set for preloadThe pre-torquing helps to insure that the new bearing is properly seated in the hub bore
44 Adjusting Manufactures procedure is found in any good shop manual Typically tapered roller bearings on the front wheels of RWD cars are adjusted for zero preloadIn most cases this means that the adjustment nut is tightened ‘finger tight’If the cotter pin does not line up with the slots in the castle nut - the nut is backed off until the cotter pin will pass throughThe thrust washer should be free to slide back and forth a little bit
45 Adjust the bearingSpin the rotor while tightening the nut. When a slight drag is felt the back off one flat [1/6 turn].
46 AdjustingSome manufactures require that the wheel bearing be preloaded with an inch / lb torque wrenchTypically the bearing is set to a higher level first [ let’s say 20 ft/lbs. ] then backed off and re-torqued to a lower value [ let’s say 25 inch / lbs ]Excessive bearing preload can cause premature bearing failureInsufficient [ loose ] preload may cause shimmy, loose steering , pulling, premature tire wear, noise and bearing damage
47 Install the retainer cap and cotter pin When a retainer cap is used the cotter pin is wrapped around the outside.
49 Wheel bearings - rear wheels of FWD cars Tapered roller bearingsSmaller but otherwise identical to tapered roller bearings used on the front wheels of RWD carsSingle row ball bearingsUsed on lightweight economy cars -Low load carrying ability of the single row bearing is not an issue here since there is so little weight being carried by itUsually permanently lubricated - but some manufactures build them with an external seal that allows them to be repacked
50 Wheel bearings - rear wheels of RWD vehicles 4 types.Single row ball bearing – light vehiclesSingle tapered roller bearing – some older domestic carsCylindrical [straight] roller bearing – domestic RWD cars and light trucksTwo tapered roller bearings on full floating axle – heavy trucks
51 Single row ball bearing Permanently lubricated by greasesInternal bearing seals keep out dirt & help retain greaseExternal axle seal prevents axle lubricant from reaching the bearingIf axle seal fails - bearing is ruined - because axle lubricant washes away grease inside bearing
52 Single row ball bearing Retained by a pressed on collar on the axle shaftCollar must be replaced when ever the bearing is replacedRemoving old collar generally requires chiseling through [ or drilling through ] the hard steel collarBearing retained to the axle housing by the brake backing plate or a separate retaining plate [ 4 bolts]
53 Single tapered roller bearings Pressed onto axle shaftsOccasionally retained to the shaft by large nutsLubricated by grease - can be repackedSeal in axle housing prevents axle lubricant from contaminating wheel bearing greaseOuter cup retained to the axle housing by retaining plate [ brake backing plate ]Preload normally adjusted by thin sheet metal shims placed between the axle housing and retaining plateSteel block in the center of the differential gearset carries axial load from the left side axle shaft to the right side shaft [ & vice versa ]
54 Cylindrical roller bearing Pressed into axle housingAxle shaft rides directly on rollersLubricated by axle lubricantLip seal on the outboard end of axle housing retains lubricantAxle shafts retained by circlips at their inboard ends
55 Service requires opening differential Service of axle and wheel bearing require that the differential cover and differential pinion shaft be removed firstWith the differential pinion shaft removed the axles are pushed slightly inward - until the circlips fall out - then the axles can be removed to gain access to the wheel bearingsIf the wheel bearing fails - the entire axle will have to be replacedSince the axle shaft rides directly on the rollers any damage to the rollers will cause damage to the axle shaftWhenever servicing these axle shafts they should be checked for spauling, brinelling and gauling