Wheel Bearings and Wheel Bearing Service

1. Wheel Bearings and Wheel Bearing Service

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 Weight • Radial 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. Traction Braking Jounce 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. Cornering Curbs and Potholes

5. Anti-friction bearings Outer Race • 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. Inner Race Rolling Element

6. Bearing types • Ball bearings • Straight roller bearings • Tapered roller bearings • Needle bearings – not used as a wheel bearing

7. Ball bearings • Ball bearings are suitable for light radial loads and very light axial loads • Component parts: • An inner race - with an external groove • An outer race - with an internal groove • A set of balls • A stamped sheet metal or plastic cage

8. Dual row ball bearings • Dual row ball bearings are one of the most common types of front wheel drive wheel bearings • When 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 bearings Outer race • On most FWD cars a single outer race housing will have two grooves - for inboard and outboard ball races • Typically there will be two inner half/races - the external groove is machined for 1/2 the width of the balls • A single, plastic cage holds the balls in their proper position and helps to retain grease Outboard inner race Inboard inner race

10. Sealed ball bearings • Wheel 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 fit • Shaft and bearing are machined for a slight interference fit • Shaft is typically .0005 inch larger than the hole in the center of the inner race • When 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 shaft • In some cases the outer race is a press fit into the housing that supports it • This 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 cars • Since 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 shafts • Without these clips the axle shaft will literally slide out of the axle housing • No 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 that • Rollers have a smaller diameter at one end than at the other • Inner race is cone shaped - with lips at both ends to retain the rollers • Sheet metal cage positions and retains rollers onto the inner race • Outer race has an internal cone [cupped] shape • Outer 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 types • Used in heavy duty applications where axial load is high - such as rear axle pinion bearings • Best design for front wheel bearing

17. Disadvantages of tapered roller bearings • Increased surface contact area adds strength but also adds drag - reduces fuel efficiency • Tapered roller bearings must be periodically adjusted for preload • Minor wear in the races and rollers allow the bearing to loosen up - permitting looseness or wobble in the wheel assembly • An adjustment nut, retained by a cotter pin is typically used for the preload adjustment

18. Wheel bearings for RWD cars • RWD vehicles use 2 tapered roller bearings for each front wheel • The inboard bearing is larger and carries most of the weight of the vehicle • The outboard bearing is smaller and carries most of the outward thrust in cornering • The offset of the rim and tire places the center of the rim nearly directly over the inboard wheel bearing

19. Non-driven wheels with tapered roller bearings Thrust Washer Inner cup Outer cup Castle cap Nut Dust cap Grease seal Inner bearing Outer bearing Hub Rotor

20. Lubrication and Sealing • The bearings are lubricated by wheel bearing grease • A lip seal is placed inboard of the inner wheel bearing to retain grease and keep dirt out • A garter spring is used to maintain a slight pressure between the lip seal and the seal surface on the spindle • A metal dust cap [ grease cap ] prevents grease from leaking to the outside

21. Wheel Spindle • The steering knuckle has a spindle [ tapered shaft ] to support the wheel bearings • Two machined surfaces on the spindle support the bearings • A third machined surface is used for the lip seal • Threads on the outboard end are cut for the preload adjusting nut • The outboard end of the spindle is usually drilled through to accommodate a cotter pin Seal surface Inner bearing surface Outer bearing surface

22. Bearing retention • Castle nuts and cotter pins are normally used to retain the bearings • Some foreign cars use a split nut with an Allen bolt clamp • Many Japanese cars use a special lock nut - and a square cut groove in the spindle • After 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 chisel • This type of nut can only be used once

23. Bearing retention • Inner race of the wheel bearings fit loosely over the spindle • Although it is not desirable to have the inner races rotate on the spindle there is very little rotation that normally takes place • If the wheel bearing fails however, the spindle may be damaged by the constant rotation of the inner race

24. Bearing retention • Outer races [ cups ] are pressed or hammered into the wheel hub • Often the hub is integral with the front brake rotors • On drum brakes the hub is usually retained to the drums by in interference fit between the wheel studs, brake drum and hub

25. Wheel Bearing Service and Replacement

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 knuckle • These 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 bolts • The 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 knuckle • Removal of the wheel bearings is a two part operation • First the hub and hub flange must be pressed out of the wheel bearing • Once 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 hammer • In other cases special factor tools may be required for safe removal and replacement of the wheel bearings

30. Tapered Roller Bearings • Removal • With the wheel is removed the dust cap, cotter pin and preload adjusting nut can be removed • The thrust washer and outer wheel bearing can now be removed • To remove the inner wheel bearing the lip seal must be removed first

31. Grease seals • The grease seals should always be replaced when servicing wheel bearings • If new lip seals are not available the seal can be removed by reinstalling the rotor , without the outer bearing • Thread the adjusting nut back onto the spindle • Pull the rotor outward - while applying downward force at the same time • The rotor will come free from the spindle - leaving the bearing, seal and nut on the spindle • Caution ! - 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 bearing • Generally caused by fatigue and high mileage • Brinelling - imprint of parallel lines on the bearing surface • Caused by impact loading or vibration while the wheels are not turning - as when it is transported on a flat bed truck • Gauling - surface of the bearing appears as though flakes of bearing material have pealed off • Caused by overheating and / or insufficient lubrication [ or wrong lubricant ] • Scuffing [ abrasive wear ] • Scratches and pitting on the bearing surfaces • Caused by abrasive material in the lubricant • Smearing - polished edge near the outside edge of the bearing • Caused by the bearing cup rotating in the hub bore • Repair necessitates replacement of both the bearing and hub [ rotor ] • Bent cage - dents or distortion in the bearing cage • Caused by mishandling during assembly

35. Spauling damage

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 preferable • Most hubs have two cast slots in the bore to facilitate bearing removal • Wipe all of the grease out of the bore to find them • A 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 spindle • Tapered 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 cage • Bearing packers force grease to fill the voids between the rollers and between the cage and rollers

39. Wheel bearing grease • Wheel bearing grease is a specialized lubricant that is designed to stay solid at relative high temperatures • Wheel bearing grease is sold in one pound plastic tubs that look like margarine containers • Chassis grease is not recommended for wheel bearings – it is normally sold in cardboard tubes that fit in grease guns • Whenever repacking wheel bearings always thoroughly clean the bearings and hubs to remove the old grease • Intermixing 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

40. Coat spindle with wheel bearing grease

41. Install rotor

42. Install outer bearing and thrust washer

43. Pre-torquing after bearing replacement. • Many manufactures recommend a bearing pre-torquing procedure • The bearing is initially pretorqued to a very high level - let’s say 60 lbs/ft • It is then loosened and then properly set for preload • The 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 preload • In 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 through • The thrust washer should be free to slide back and forth a little bit

45. Adjust the bearing • Spin the rotor while tightening the nut. When a slight drag is felt the back off one flat [1/6 turn].

46. Adjusting • Some manufactures require that the wheel bearing be preloaded with an inch / lb torque wrench • Typically 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 failure • Insufficient [ 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.

48. Install dust cap

49. Wheel bearings - rear wheels of FWD cars • Tapered roller bearings • Smaller but otherwise identical to tapered roller bearings used on the front wheels of RWD cars • Single row ball bearings • Used 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 it • Usually 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 vehicles • Single tapered roller bearing – some older domestic cars • Cylindrical [straight] roller bearing – domestic RWD cars and light trucks • Two tapered roller bearings on full floating axle – heavy trucks