2013-2025 Mazda CX-5 & 2014-2021 Mazda6 Rear Hub Bearing Noise: Diagnosis & Replacement

Symptoms of a Failing Rear Hub Assembly

A failing rear hub bearing typically gives several warning signs. The most common symptom is a noise that changes with vehicle speed. It's crucial to identify these sounds correctly, as Mazda has issued a service alert (SA-032/21) warning that wheel bearing noise is often misdiagnosed as a more expensive differential or transmission problem.

• Humming, Roaring, or Grinding Noise: This is the classic sign of a bad wheel bearing. The noise typically starts as a faint hum and gets progressively louder over time. It is directly related to wheel speed, not engine speed, and will be present whether you are accelerating, coasting, or in neutral.
• Noise Changes While Turning: 🎬 Watch: How to tell which wheel bearing is bad A key diagnostic clue is a change in the noise when turning or swerving. For example, if you swerve to the left, the vehicle's weight shifts to the right-side wheels. If the noise gets louder during a left turn, it often indicates the right rear bearing is failing, and vice-versa.
• Vibration or Wobble: In more advanced stages of failure, you may feel a vibration through the floor or steering wheel. In severe cases, you might feel a wobble from the rear of the car, indicating excessive play in the bearing.
• ABS Warning Light: The hub assembly contains the sensor ring for the wheel speed sensor. If the bearing develops excessive play or the sensor ring is damaged, it can cause an erratic signal, triggering the ABS and traction control warning lights on your dashboard.
• Uneven Tire Wear: A worn and loose wheel bearing can affect the wheel's alignment, leading to abnormal or accelerated tire wear on the affected corner.

Known Issues, TSBs, and Recalls

While there are no direct safety recalls for the hub assemblies on these vehicles, Mazda has released several Technical Service Bulletins (TSBs) that are highly relevant to diagnosing and repairing rear-end noises.

TSB SA-032/21: Wheel Bearing Noise Misdiagnosed as Drivetrain Failure

This is the most important bulletin for any owner experiencing a humming or growling noise. Mazda noted that many warranty claims were being filed for expensive differential, transfer case, and transmission repairs when the actual cause was a simple wheel bearing failure. A technician may mistake the sound's origin, leading to a costly and incorrect repair. If you are quoted for a differential replacement, make sure the wheel bearings have been thoroughly ruled out first.

TSB for Rear Backing Plate

Mazda issued a service bulletin related to a "howling-type sound" from the rear of the vehicle caused by a faulty hub bearing. The investigation found that unevenness on the surface of the brake backing plate (the thin metal shield behind the brake rotor) could cause the new hub to be installed improperly, leading to premature failure. The TSB instructs technicians to replace the rear hub assembly and the backing plate as a set to ensure a proper, flat mounting surface. When replacing a hub, especially if it has failed prematurely, inspecting or replacing the backing plate is a wise precaution.

TSB 02-015/18: Broken Rear Coil Spring

For 2013-2018 Mazda CX-5 models, Mazda issued a TSB regarding a knocking noise or a lower-than-normal rear ride height caused by a broken rear coil spring. Corrosion can cause the bottom of the spring to fracture. While not a hub issue, the resulting noise could be confused with a bad bearing or other suspension problem, making it a relevant diagnostic consideration.

Vehicle Fitment and Part Variants

This rear hub assembly is shared between the 2014-2021 Mazda6 and the 2013-2025 Mazda CX-5 due to their shared platform architecture. However, there are critical differences based on the drivetrain.

• 2014-2021 Mazda6: All Mazda6 models of this generation are Front-Wheel Drive (FWD). They use the same rear hub assembly.
• 2013-2021 Mazda CX-5: These models were available in both FWD and All-Wheel Drive (AWD). The FWD and AWD models use different rear hub assemblies. It is critical to order the correct part for your specific drivetrain. The hub for the AWD model is designed to have the drive axle pass through it.
• 2022-2025 Mazda CX-5: Aftermarket data suggests that from 2022 onward, Mazda may have begun using the same rear hub assembly for both FWD and AWD models, but it is always best to verify the part number with your vehicle's VIN.

Buying a Used Hub Assembly

A high-quality, low-mileage used OEM hub assembly can be a great value compared to a new part from the dealer or a cheap aftermarket alternative. OEM parts are manufactured to a higher standard than many aftermarket options, which can sometimes fail prematurely. Here’s what to look for when buying used:

• Verify Part Numbers: Check the stamped part number against the list of known OEM numbers. Pay close attention to the supersession history; a later part number like KD35-26-15XD is a revised, newer version of an older part like KD35-26-15XB.
• Check for Play: With the hub in hand, try to wiggle the center flange relative to the outer mounting bracket. There should be absolutely no play or looseness. The bearing should spin smoothly with some resistance, but without any grinding, catching, or roughness.
• Inspect the ABS Sensor and Connector: Ensure the integrated ABS sensor is not physically damaged and the electrical connector pins are clean and straight. A damaged sensor will render the part useless.
• Mileage and Condition: Ask for the mileage of the donor vehicle. While failures can happen at any time, bearings from vehicles with under 100,000 miles are generally a safer bet. Avoid hubs that show heavy corrosion or signs of impact damage.
• Confirm Drivetrain Compatibility: For CX-5 owners, double-check if the part came from an AWD or FWD vehicle to ensure it matches yours.

Cost of Replacement

The cost to replace a rear hub assembly can vary significantly based on the parts you choose and who performs the labor.

Replacement Overview & Torque Specs

Replacing the rear hub assembly is a feasible DIY job for someone with moderate mechanical experience and the right tools. The process does not require a press, as the hub is a bolt-in unit.

1. Safely raise and support the vehicle on jack stands and remove the rear wheel.
2. Remove the brake caliper and its mounting bracket. Hang the caliper securely with a hook or wire; do not let it hang by the brake hose.
3. Remove the brake rotor. If it is stuck, a few taps with a hammer on the area between the lug studs can help break it free.
4. Disconnect the ABS wheel speed sensor connector. Remove the 10mm bolt holding the sensor to the knuckle and carefully wiggle the sensor out.
5. From behind the knuckle, remove the four bolts that secure the hub assembly. Access to the top bolt may be partially blocked by the shock absorber.
6. With the bolts removed, the hub may be seized in the knuckle. Use a hammer or dead blow to strike the old hub from behind to knock it out.
7. Thoroughly clean the mounting surface on the knuckle and the bore where the hub sits. Use a wire brush or wheel to remove all rust and debris. This is critical for the longevity of the new bearing. Consider applying a thin layer of anti-seize to the knuckle surface to prevent future corrosion.
8. Install the new hub assembly, ensuring the dust shield is correctly positioned. Tighten the four mounting bolts in a star pattern to the correct torque.
9. Reassemble the remaining components in the reverse order of removal.

Frequently Asked Questions (FAQ)