2023 Lexus RZ450e Front Knee & Hub Assembly: The Critical Hub Bolt Warning

Critical Safety Warning: Hub Bolts

Known Issues, TSBs, and Recalls

As a relatively new model, the 2023 RZ450e does not have a long history of common failures. However, a few key items are documented.

• TSB L-SB-0037-23: Understanding Hub Bolts and Hub Nuts: This is the most critical document related to the front knee assembly. It details the differences between the hub bolt system on the RZ450e and traditional stud/nut systems, emphasizing that using incorrect fasteners or wheels can cause the wheel to come loose.
• Unrelated HVAC Recall: There is a recall for the HVAC control unit software which can affect the windshield defroster's performance in very cold weather. This issue is electronic and does not involve the mechanical suspension components of the front knee.

Symptoms of a Failing Front Knee or Wheel Bearing

Failure in the front knee assembly typically originates from the wheel bearing. Because the bearing is integrated into the hub, the entire hub assembly must be replaced. Here are the signs of a bad wheel bearing/hub.

1. Grinding, Humming, or Growling Noise

This is the most common symptom. The noise comes from the front of the vehicle and typically starts as a faint hum, getting progressively louder over time. The sound changes with vehicle speed—the faster you go, the louder it gets. A key diagnostic clue is that the noise will often change pitch or intensity when you turn; for example, a failing left front wheel bearing will usually get louder when turning right, as more load is placed on it.

2. Steering Wheel Vibration

As the bearing surfaces wear and become rough, they can cause a vibration that you feel in the steering wheel. Unlike a tire imbalance that often occurs only at a specific speed range, a bad bearing vibration tends to be constant and worsens as speed increases.

3. Excessive Wheel Play or Wobble

A severely worn bearing will allow for movement or 'play' in the wheel. To check this, the vehicle must be safely lifted so the tire is off the ground. Grab the tire at the top and bottom (12 and 6 o'clock positions) and try to rock it in and out. If you feel any clunking or movement, the bearing is worn and requires immediate replacement. A healthy bearing will have no noticeable play.

4. ABS Warning Light

The wheel speed sensor for the Anti-lock Braking System (ABS) is mounted on the steering knuckle and reads a magnetic ring on the wheel hub assembly. If the bearing develops excessive play, it can disrupt the signal from the sensor to the ABS control module, triggering the ABS warning light on your dashboard. An OBD2 scanner capable of reading ABS codes can confirm a fault related to a specific wheel speed sensor.

Buying a Used 2023 RZ450e Front Knee Assembly

For a new vehicle like the RZ450e, a low-mileage used OEM knee assembly from a reputable recycler can be an excellent value, offering factory-grade materials and perfect fitment. Since these parts are not yet common in the aftermarket, a used OEM part is often the best alternative to an expensive new dealer part.

What to Inspect:

• Check for Impact Damage: Visually inspect the entire assembly, especially the steering knuckle, for any cracks, bends, or significant scrapes that indicate it came from a vehicle in a major collision. A bent knuckle will make alignment impossible.
• Spin the Hub: With the assembly on the ground, try to spin the wheel hub by hand. It should rotate smoothly and silently. Any grinding, roughness, or noise indicates the bearing is bad.
• ABS Sensor and Wire: Ensure the ABS sensor is present and that its wiring harness has not been cut or damaged during removal from the donor vehicle.
• Ball Joint and Bushings: If the control arms are included, check the condition of the rubber bushings and the ball joint boot.

Compatibility Checks:

• Left vs. Right: The driver's side (Left) and passenger's side (Right) knuckles are not interchangeable. Part number 43202-42010 is for the left side.
• Hub Assembly Part Numbers: The original hub assembly is part number 43550-42050. This has been superseded by part number 43550-46010. Both should be compatible, but the newer number is preferred.
• Included Components: Clarify exactly what is included. A 'knee' assembly should include the knuckle, hub/bearing, and brake dust shield. It may or may not include the strut, control arm, or axle shaft.

Replacement Overview & Special Procedures

Replacing a front knee assembly is an advanced repair that directly impacts vehicle safety. It requires disconnecting major suspension, steering, and braking components.

The general steps involve:

1. Lifting and supporting the vehicle and removing the wheel.
2. Removing the brake caliper, caliper bracket, and rotor.
3. Removing the axle nut and pushing the axle shaft out of the hub.
4. Disconnecting the ABS wheel speed sensor connector.
5. Separating the steering tie rod end and the lower ball joint from the knuckle.
6. Unbolting the knuckle from the base of the strut assembly.
7. Installation is the reverse of removal. Crucially, new hub bolts and a new axle nut must be used and torqued to the exact factory specification.

Cost of Replacement

Prices can vary based on your location and choice of parts. The RZ450e is new, so aftermarket options are scarce, making used OEM a cost-effective choice.

Frequently Asked Questions (FAQ)