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TRN-AUTO19-04 · Lesson 5 · 18 clock hours · lab

Wheel Bearings and Hubs: Diagnosis and Service

Objective. Students will diagnose wheel bearing wear by noise, play, and temperature methods, and replace both a unitized hub-and-bearing assembly and a tapered roller bearing set to manufacturer specifications.

⚠ Pending professional review

This lesson, its worked examples and its practice questions has not yet been verified by a certified examiner or master technician in the trade or by a certification or approval body. It is a study draft and may contain errors. Do not use it as instructions for work on a job site or on live equipment. Always follow your instructor, your supervising professional, and current official references and regulations.

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Wheel Bearings and Hubs: Diagnosis and Service

Wheel bearings allow the wheel and tire assembly to rotate smoothly on the spindle or axle with minimal friction while supporting the full weight of the vehicle. When a bearing fails, the result can be noise, uneven tire wear, loose steering, or—in the worst case—a wheel separating from the vehicle. Accurate diagnosis and correct installation are non-negotiable skills for any automotive technician.

How Wheel Bearings Work

Two bearing designs dominate automotive service:

Tapered roller bearings use cone-shaped rollers held between an inner race (cone) and an outer race (cup). They handle both radial loads (the vehicle's weight pressing down) and axial (thrust) loads (side forces in cornering). Because the bearing clearance is adjustable, the technician sets a precise preload or end-play during installation. Tapered roller bearings are common on the non-driven rear wheels of rear-wheel-drive vehicles and on some front hubs.

Unitized hub-and-bearing assemblies (also called sealed or cartridge bearings) contain two rows of ball or roller bearings pre-packed with grease and sealed for life inside a single flanged unit. Preload is set at the factory; the technician simply torques the hub nut and the assembly bolts to specification. These are standard on most front-wheel-drive and many modern all-wheel-drive vehicles.

Diagnosing Wheel Bearing Wear

Noise Method

A failing wheel bearing typically produces a growling, rumbling, or humming noise that changes with vehicle speed rather than engine rpm. The noise often shifts when the vehicle is loaded laterally—if it gets louder on left turns, the right front bearing is suspect (load transfers to the outside wheel). Use a mechanic's stethoscope with the vehicle on a lift and wheels spinning to isolate the noisy corner. Never reach toward rotating components.

Play Method

With the vehicle safely lifted on approved jack stands or a frame-contact lift and the parking brake released:

Mount a dial indicator on a magnetic base against the hub face or rotor hat to measure actual play in thousandths of an inch. Always compare your reading to the OEM specification—most sealed hub assemblies allow essentially zero play; tapered roller bearings on passenger cars may allow a small amount of end-play per specification.

Temperature Method

After a short road test, use an infrared (non-contact) thermometer to compare hub temperatures at all four corners. A bearing generating excessive friction will run noticeably hotter than the others. Note: brake drag can also raise hub temperature, so rule that out first.

Safety

Replacing a Unitized Hub-and-Bearing Assembly

1. Loosen the axle (hub) nut while the wheel is on the ground.

2. Lift and support the vehicle; remove the wheel.

3. Remove brake components as needed for access (caliper, rotor).

4. Disconnect the ABS wheel speed sensor connector.

5. Remove the hub assembly mounting bolts from the steering knuckle.

6. Use a hub puller if the assembly is pressed onto the axle stub; never strike the CV axle.

7. Clean the knuckle bore and mounting surfaces.

8. Install the new assembly and hand-thread all bolts; torque in a star pattern to the OEM specification.

9. Install and torque the axle nut to specification.

10. Reinstall brakes, wheel, and lower the vehicle. Verify ABS sensor connector is seated.

Packing and Installing Tapered Roller Bearings

Force fresh NLGI Grade 2 grease through a bearing packer tool until grease extrudes uniformly between all rollers. Pack the hub cavity (do not fill it completely—leave room for grease expansion). Install the inner bearing, grease seal, and rotor/hub assembly onto the spindle. Install the outer bearing and washer, then the castellated nut. Tighten the nut to specification while rotating the hub to seat the bearings, then back off and re-torque to the final specification per the OEM procedure—this sets the correct preload or end-play. Insert a new cotter pin through the nut slot and spindle hole; bend the legs securely.

Documentation

Record all measurements, torque values, parts installed, and pass/fail decisions on the repair order. Accurate documentation protects both the customer and the technician and is required for professional practice.

Key terms10

Axial (thrust) playMovement of the wheel hub along the axis of the spindle or axle; excessive axial play indicates bearing wear and is measured with a dial indicator at the 12 and 6 o'clock positions.
Radial playMovement of the wheel hub perpendicular to the spindle axis; measured with a dial indicator at the 9 and 3 o'clock positions and indicates radial bearing wear.
Unitized hub-and-bearing assemblyA factory-sealed, non-adjustable cartridge unit that combines the hub flange and double-row bearing in one assembly; preload is set at the factory and the unit is replaced as a complete piece.
Tapered roller bearingA bearing using cone-shaped rollers between tapered inner and outer races, capable of handling both radial and axial loads; end-play or preload is adjusted by the technician during installation.
PreloadA slight internal compressive force applied to a bearing during installation to eliminate play and extend service life; too much preload causes overheating, too little allows play.
NLGI Grade 2A grease consistency classification from the National Lubricating Grease Institute; Grade 2 is the most common specification for wheel bearing grease in automotive applications.
Castellated nutA fastener with slots cut into its top surface that align with a hole in the spindle, allowing a cotter pin to lock the nut in position and prevent loosening.
ABS tone ringA toothed ring integrated into or attached to the hub or bearing assembly that generates a signal for the wheel speed sensor; it must not be damaged during bearing service.
Dial indicatorA precision measuring tool that displays small linear movements in thousandths of an inch (or hundredths of a millimeter) on a graduated face; used to measure wheel bearing play.
Hub pullerA specialized tool used to separate a pressed hub or bearing assembly from the steering knuckle or spindle without damaging adjacent components.

Worked examples4

1. With a dial indicator mounted on the hub face, you measure 0.005 in. of axial play. The OEM specification for this unitized bearing states the maximum allowable play is 0.002 in. By how much does the measured play exceed the limit, and what is the correct service action?
  1. Identify the measured value: 0.005 in.
  2. Identify the OEM maximum allowable value: 0.002 in.
  3. Subtract the limit from the measured value: 0.005 in. − 0.002 in. = 0.003 in. excess play.
  4. Because the measurement exceeds the specification, the bearing is worn beyond acceptable limits.
  5. Service action: replace the unitized hub-and-bearing assembly.
Answer: The play exceeds the specification by 0.003 in.; the unitized hub-and-bearing assembly must be replaced.
2. After packing a tapered roller bearing, you torque the castellated spindle nut to seat the bearings, then back it off. The OEM procedure then calls for tightening the nut to 17 ft-lb while rotating the hub, then backing off exactly 1/2 turn to achieve final end-play. If each flat of the six-sided nut equals 60° of rotation, how many degrees is 1/2 turn, and how many flats does that represent?
  1. Calculate degrees in 1/2 turn: 360° ÷ 2 = 180°.
  2. Calculate degrees per flat on a six-sided (hex) nut: 360° ÷ 6 = 60° per flat.
  3. Calculate number of flats in 180°: 180° ÷ 60° per flat = 3 flats.
  4. Back the nut off 3 flats (180°) to reach the final adjustment position.
Answer: 1/2 turn equals 180°, which corresponds to backing off 3 flats on a six-sided nut.
3. You use an infrared thermometer after a road test and read these hub temperatures: LF 155°F, RF 210°F, LR 158°F, RR 162°F. The brake caliper on the RF slides freely and the rotor shows no drag. What does the temperature difference suggest, and how large is the RF deviation from the average of the other three corners?
  1. Calculate the average of the three normal corners: (155 + 158 + 162) ÷ 3 = 475 ÷ 3 = 158.3°F.
  2. Calculate the deviation of the RF: 210°F − 158.3°F = 51.7°F above average.
  3. No brake drag is present, so the heat source is bearing friction.
  4. A difference of approximately 52°F with no brake drag strongly indicates a failing RF wheel bearing generating excessive friction.
Answer: The RF hub runs approximately 52°F hotter than the average of the other three corners; with brake drag ruled out, a failing right-front wheel bearing is indicated.
4. The OEM torque specification for a hub-and-bearing assembly bolt is listed as 85 N·m. Your torque wrench is calibrated in ft-lb. Using the conversion 1 ft-lb = 1.356 N·m, what is the equivalent specification in ft-lb, rounded to the nearest whole ft-lb?
  1. Set up the conversion: ft-lb = N·m ÷ 1.356.
  2. Divide: 85 ÷ 1.356 = 62.68 ft-lb.
  3. Round to the nearest whole number: 63 ft-lb.
  4. Set your torque wrench to 63 ft-lb to match the OEM specification.
Answer: 85 N·m is approximately 63 ft-lb.
In class: Students rotate each wheel on four shop vehicles while listening for noise and checking for axial and radial play using a dial indicator; they classify each bearing and document findings on a repair order. · Instructor demonstrates hub-and-bearing assembly removal and installation on a front-wheel-drive vehicle; students repeat the procedure on an assigned vehicle, documenting torque steps. · Students pack a tapered roller bearing with the correct grease type, install it with the proper preload adjustment procedure, and install the cotter pin correctly.
Materials: Dial indicators, stethoscope, infrared thermometer, hub pullers, axle nut sockets, impact wrench, torque wrench, bearing packer tool, wheel bearing grease (NLGI Grade 2 or per OEM spec), unitized bearing assemblies, tapered roller bearing sets, cotter pins, OEM service manuals
Check: Completed repair order with dial indicator measurements and pass/fail decision reviewed by instructor; installed bearing assembly must show zero detectable play at the wheel rim and correct torque documented — pass requires both conditions met.

Practice check8

Answer each question, then check it. Nothing is recorded; this is your own practice.

Suspension and Steering (A4)
1. A vehicle produces a rumbling noise that increases when the driver turns slightly to the right but decreases when turning slightly to the left. Which wheel bearing is most likely failing?
Suspension and Steering (A4)
2. A technician measures 0.006 in. of axial play at the right front hub on a vehicle with a unitized sealed bearing assembly. The OEM maximum is 0.002 in. What is the correct repair?
Suspension and Steering (A4)
3. When installing a new cotter pin after adjusting a tapered roller bearing, which practice is correct?
Suspension and Steering (A4)
4. Which grease characteristic is described by the NLGI Grade 2 designation?
Suspension and Steering (A4)
5. A technician is about to remove a front hub-and-bearing assembly from a front-wheel-drive vehicle. What is the FIRST safety step before loosening the large axle (hub) nut?
Suspension and Steering (A4)
6. A dial indicator is placed against the hub face with the probe parallel to the axle centerline. The technician pushes and pulls the wheel in and out and reads a total movement of 0.004 in. This measurement evaluates which type of bearing play?
Suspension and Steering (A4)
7. After road testing a vehicle, an infrared thermometer shows one hub is significantly hotter than the other three. The technician confirms the brakes are not dragging on that corner. What is the most likely cause?
Suspension and Steering (A4)
8. Which condition MUST be met before a wheel bearing service job can be signed off on the repair order, according to professional practice and the lab check criteria?
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