2014-2020 BMW i8 Door Hinge and Strut Guide: Fixing Sagging and Failing Doors

Understanding the i8's Unique Door System

The 2014-2020 BMW i8's doors are a defining feature, but they also have unique service points. It is critical to distinguish between two key parts: the main door hinge assembly and the gas-pressurized strut. The hinge is the large, robust metal pivot (OEM part numbers 51007312702 for the right side, 51007312701 for the left) that attaches the door to the car's A-pillar. The gas strut (OEM part number 51227375528) is the component that most commonly fails. It looks like a small shock absorber and is responsible for lifting the door and holding it in the open position.

Symptoms of a Failing Door Hinge or Strut

Diagnosing door problems on an i8 usually points to one of a few common issues. Pay close attention to how the door behaves during opening and closing.

1. Door Will Not Stay Open or Sags

This is the most common symptom and almost always indicates a failed gas strut. You may notice that you have to manually push the door up the last few inches, or it may not stay up at all, especially in cold weather. If you open the door and it immediately starts to fall, the gas strut has lost its pressure and can no longer support the door's weight.

2. Creaking or Grinding Noises

A creaking sound when opening or closing the door can also be a sign of a failing gas strut. In some cases, simply rotating the plastic sleeve around the strut can resolve the noise, but if it persists, the strut is likely the culprit. A more severe grinding or popping noise could indicate a problem with the main hinge assembly itself, often from a previous impact or stress.

3. Door Fails to Latch or Open Electronically

If the door closes but doesn't latch, or if it fails to unlatch when you use the handle, the problem is likely with the door lock actuator, not the hinge. This can sometimes be caused by a weak 12-volt vehicle battery or a weak key fob battery, which causes the door lock to enter a temporary failsafe mode. A blinking LED on the door release switch is an indicator of a fault in the lock system.

Known Issues, TSBs, and Recalls

Service Bulletin SIB 51 31 19: Door Will Not Open or Close

BMW issued a technical service bulletin for i8 models where a door will not latch or unlatch. The cause is often a low voltage supply from the main 12V battery or the key fob battery. This can put the door lock actuator in a failsafe mode. The official procedure involves fixing the underlying battery issue and then resetting the door lock by disconnecting the door's isolating plug, which is accessible after removing the rear section of the front wheel arch cover.

Gas Strut Wear and Tear

The gas struts are considered a wear-and-tear item by BMW, with some service schedules recommending replacement every few years or every second oil service. Owners report them weakening in as little as one year or 16,000-17,000 miles. This is not a defect, but a regular maintenance item due to the stress of lifting the heavy doors.

Cracked Wiring Harness Cover

Some owners have experienced the protective plastic cover over the door's wiring harness becoming brittle and cracking over time. This is caused by the stress of the door's movement. If the cover breaks, it could potentially allow moisture to damage the wiring within, leading to electrical issues. Applying a plastic and rubber protectant can help keep the material flexible and reduce the risk of cracking.

Buying a Used BMW i8 Door Hinge

A used OEM hinge assembly can be a cost-effective solution, especially since quality aftermarket options are not available. However, careful inspection is crucial before buying.

• Test the Gas Strut: The most important check. If the used hinge assembly comes with the gas strut attached, you must assume the strut is likely worn. There is no reliable way to test its strength without installing it. Budget for a new pair of gas struts (~$200) as part of the job.
• Inspect for Cracks and Bends: The hinge is made of metal but can be damaged in a collision. Carefully inspect the entire assembly for any hairline cracks, especially around the mounting points and pivot areas. Check for any signs of bending or deformation that would prevent proper alignment.
• Verify the Part Number: Double-check that you are buying the correct part for your vehicle. The left (driver) and right (passenger) side hinges are different parts. Ensure it is for a Coupe (I12) and not a Roadster (I15).
• Check All Included Components: A complete used assembly should include the main hinge body and potentially the mounting bolts. Clarify with the seller exactly what is included.

Replacement and Installation

The difficulty of this job depends entirely on which part you are replacing.

Gas Strut Replacement (DIY)

• Difficulty: 2 out of 5
• Time: 0.5 - 1 hour
• Summary: This is a straightforward DIY job. You will need a prop (like a telescoping hood prop) to securely hold the door in its fully open position. The strut is held on by a metal locking clip at each end. Using pliers, you pull the clip to unlock it, then pop the strut off the ball joints on the hinge and door. The new strut snaps into place, and the locking clips are re-secured.
🎬 Watch this video for a step-by-step gas strut replacement walkthrough.

Full Hinge Assembly Replacement (Professional Recommended)

• Difficulty: 5 out of 5
• Time: 3 - 5 hours
• Summary: This is a complex and difficult job that is not recommended for beginners. It requires at least two people to manage the weight and position of the door. The process involves removing the front wheel, the wheel arch liner, and the entire front fender to access the hinge bolts on the car's body. The door's wiring harness must be disconnected. After swapping the hinge, the door must be painstakingly realigned to ensure proper panel gaps and that it latches correctly. Specific torque specs are required for reassembly.

Cost Comparison

Frequently Asked Questions (FAQ)