2014-2020 BMW i8 Front Knee Assembly: Noises, TSBs, and Replacement Guide

Symptoms of a Failing Front Knee Assembly

Failure of the front knee assembly on a BMW i8 is uncommon and almost always caused by a significant impact, such as hitting a curb, a deep pothole, or being in a collision. The knuckle itself is a durable, solid part, but it can bend or crack. More often, the symptoms people notice are from a worn wheel bearing, which is housed within the knee assembly.

Noises

• Grinding or Humming: A continuous grinding, humming, or rumbling noise from one of the front wheels that gets louder with speed is a classic sign of a bad wheel bearing. The noise may change pitch or intensity when you turn the steering wheel; for example, a failing left front bearing may get louder when turning right as more weight is transferred to it.
• Clunking or Popping: A sharp clunking or popping sound when going over bumps or making tight, low-speed turns (like in a parking lot) can indicate a cracked knuckle or worn-out ball joints or control arm bushings connected to it.
• Ticking When Cornering: Some BMW models can develop a ticking noise from the front wheel area during low-speed cornering. While this can have several causes, it's a symptom to investigate in the front wheel assembly area.

Steering and Handling Issues

• Vehicle Pulling to One Side: A bent steering knuckle will alter the suspension geometry, causing the car to pull to the left or right even when the steering wheel is straight. This issue will persist even after a wheel alignment.
• Vibrating or Loose Steering Wheel: A vibration that can be felt through the steering wheel, especially at highway speeds, can be caused by a worn wheel bearing creating excessive play. The steering may feel vague or less responsive than usual.
• Uneven Tire Wear: A key sign of a bent knuckle is rapid and uneven wear on the inside or outside edge of one specific tire. This happens because the knuckle is no longer holding the wheel at the correct angle (camber), causing the tire to lean in or out.

Known Issues, TSBs, and Recalls for 2019 BMW i8

While there are no recalls specifically for the steering knuckle, several official communications are relevant to the front suspension and overall vehicle safety.

Technical Service Bulletins (TSBs)

• TSB B360121: Addresses a condition where the front end can feel slightly misaligned, causing a "jerking" or "clunking" sensation at low speeds with a large steering angle, particularly in cold temperatures (below 40°F).
• TSB B340517: Pertains to a "ticking noise while cornering without the brakes applied" that is noticeable at low speeds.

Safety Recalls

• NHTSA Recall #19V599000: This recall was issued for a faulty Electric Motor Electronics (EME) module. A problem with an internal circuit board could cause the high-voltage system to shut down, resulting in a sudden loss of propulsion. The remedy involves replacing the EME module at a dealership.
• NHTSA Recall #20V601000: Affecting some 2020 models, this recall was for potential debris inside the hybrid battery cells, which could cause a short-circuit and increase fire risk.

Buying a Used 2014-2020 i8 Front Knee Assembly

Due to the high cost of new OEM parts for the i8, a used OEM knee assembly is a smart, cost-effective option. These parts are designed for the life of the vehicle and typically only require replacement due to impact damage. Aftermarket options for the i8 knuckle are virtually nonexistent, making recycled OEM parts the best alternative to new.

Inspection Checklist

• Check for Cracks or Bending: Carefully inspect the entire part, especially around the mounting holes for the control arms, strut, and brake caliper. Pay close attention to the tapered holes for the ball joints and tie rod end; any distortion here means the part is unusable.
• Verify Hub and Bearing Inclusion: The most important check is to confirm whether the assembly includes the wheel hub and bearing. Many recyclers sell the "knee" as a complete unit with these parts pressed in and ready to install. A knuckle sold without the hub/bearing will require you to purchase one separately and have it professionally pressed in, adding significant cost and labor.
• Assess the Wheel Bearing: If the bearing is included, try to spin it by hand. It should be smooth and silent. Any roughness, grinding, or noticeable play (wobble) means the bearing is bad and will need to be replaced.
• Mileage Considerations: For the knuckle itself, mileage is not a major concern. For the included wheel bearing, lower mileage is always better. BMW wheel bearings can sometimes become noisy after 50,000 miles, especially on cars that have been driven hard.

Cost Comparison (2014-2020 BMW i8 Front Knee)

Prices can vary based on location and supplier, but this provides a general estimate for one side.

Replacement and Installation

Replacing the front knee assembly is an advanced job that is likely beyond the scope of most DIY mechanics due to the complexity of the i8's suspension and the need for special tools. The wheel hub/bearing for the i8 is a bolt-in unit, which is simpler than older press-in designs.

Key Procedures

1. The vehicle must be safely raised and supported on jack stands.
2. The wheel, brake caliper, caliper bracket, and brake rotor must be removed.
3. The axle nut must be removed to allow the drive axle to be separated from the wheel hub.
4. The connections to the upper control arm, lower control arm (tension strut), and tie rod end must be disconnected from the knuckle.
5. The lower strut bolt that clamps the strut into the knuckle must be removed.
6. The old assembly is removed, and the new one is installed by reversing the steps.

Torque and Alignment Specifications

Specific torque specs for the BMW i8 are not widely published in public-facing documents and should be sourced from BMW's official Technical Information System (TIS). Using incorrect torque values can lead to component failure or unsafe handling. Likewise, the vehicle requires a precise four-wheel alignment to factory specifications after the knee assembly is replaced. This is not an optional step; skipping it will cause poor handling and destroy your tires.

Frequently Asked Questions (FAQ)