1995-2001 BMW 750i Flex Plate: Diagnosing Noises and Vibration from the M73 V12
This guide covers the common failure symptoms, inspection points for used parts, and replacement costs for the flex plate on the E38 BMW 750i with the 5.4L V12 engine.
- Replacement is a major repair that requires removing the entire transmission, making labor the biggest cost factor.
- The most common symptom of failure is a metallic rattling or knocking noise at idle, which can be mistaken for serious engine failure.
- When buying a used part, the most important checks are for hairline cracks around the bolt holes and for damaged teeth on the starter ring gear.
- This flex plate is specific to the M73/M73N 5.4L V12 engine; parts from other BMW models are not compatible.
Common Failure Symptoms
A failing flex plate typically announces itself with distinct noises and vibrations. Because replacement is a labor-intensive job, it's important to diagnose the issue correctly. The sound is often misdiagnosed as a more serious internal engine problem, like a rod knock.
- Rattling or Knocking at Idle: The most common symptom is a metallic rattling, clunking, or knocking sound coming from the area where the engine meets the transmission. This noise is often most noticeable at idle in Park or Neutral and may change or disappear as engine RPMs increase.
- Grinding or Whining During Engine Start: If the teeth on the starter ring gear are damaged, you may hear a loud grinding or whining sound when you try to start the car. In some cases, the starter may have difficulty turning the engine over at all.
- Noise When Shifting Gears: You might hear a distinct clunk or knock when shifting from Park into Drive or Reverse.
- Vibrations: A cracked or warped flex plate will be out of balance, causing a noticeable vibration that can be felt through the floor or driver's seat. This vibration often gets worse as you accelerate.
- Transmission and Power Issues: In severe cases, a badly damaged flex plate can lead to issues like transmission slippage or a feeling of power loss.
Known Issues, TSBs, and Recalls
As of mid-2026, there are no specific recalls or Technical Service Bulletins (TSBs) from BMW or the NHTSA that directly address flex plate failure on the 1995-2001 BMW 750i. The recalls issued for this vehicle range concern other components like the auxiliary cooling fan, brake light switch, and tires. While there are no widespread, documented design flaws with the M73 engine's flex plate, failures can still occur due to age, stress, and mileage. The most common cause of a cracked flex plate is misalignment between the engine and transmission, which causes the plate to flex excessively until it fatigues and breaks.
Pro Tip: The E38 7-series is known for other issues that can cause vibrations, such as worn front suspension components (the "shimmy") and failing vibration dampers. It's important to rule these out before committing to a transmission removal for flex plate replacement.
Buying a Used Flex Plate: A Buyer's Guide
Since new OEM flex plates for the M73 engine are often discontinued or difficult to find, a quality used OEM part is an excellent alternative. A used original part is often superior to a cheap aftermarket replacement in terms of material quality and proper balance. Before purchasing, perform a thorough inspection.
What to Inspect on a Used Part:
- Check for Cracks: This is the most critical inspection. Carefully examine the entire surface of the plate for hairline cracks. Pay special attention to the area around the central crankshaft mounting holes and the outer torque converter bolt holes, as this is where stress cracks typically form.
- Inspect the Ring Gear Teeth: Look at the teeth on the outer starter ring gear. Check for any that are chipped, excessively worn, or broken off. Damaged teeth can cause starting problems and damage the starter motor.
- Verify Flatness: Place the flex plate on a known flat surface to check for any signs of warping or bending. A warped plate will cause immediate vibration issues and can damage transmission seals.
- Confirm Part Number: Ensure the part number matches what is required for your M73/M73N engine. The primary OEM part number is 11-22-1-742-699. Using a flex plate from a different engine (like the M62 V8) will not work.
Replacement Cost & Difficulty
Replacing the flex plate on a BMW 750i is a difficult and expensive job due to the high amount of labor required.
- Difficulty Rating: 5 out of 5 (Professional level)
- Primary Challenge: The transmission must be completely removed from the vehicle to access the flex plate, which is bolted to the back of the engine's crankshaft. This is a complex procedure on a V12-powered E38.
- DIY Feasibility: Not recommended for DIY mechanics without a vehicle lift, a transmission jack, and extensive experience.
| Part/Service | Estimated Cost |
|---|---|
| New OEM Part | $400 - $650+ (Often discontinued/special order) |
| New Aftermarket Part | $250 - $450 |
| Used OEM Part | $75 - $150 |
| Shop Labor Cost | $1000 - $1800+ |
Warning: Always replace the flex plate mounting bolts with new ones during installation. These are torque-to-yield bolts and are designed for single use. Reusing old bolts can lead to them backing out or breaking, causing catastrophic damage.
Frequently Asked Questions (FAQ)
What is the difference between a flywheel and a flex plate?
A flywheel is used on vehicles with a manual transmission, while a flex plate is used on vehicles with an automatic transmission, like the BMW 750i. A flywheel is much heavier and stores rotational energy, while a flex plate is a lighter, thinner disc that simply connects the engine to the torque converter.
Can I drive my car with a cracked flex plate?
It is strongly advised not to drive with a suspected cracked flex plate. A failing plate can cause a loss of power to the wheels, potentially leaving you stranded. If the plate breaks apart at speed, it can cause severe damage to the transmission bellhousing and the back of the engine block.
Do I need to replace the flex plate bolts?
Yes. BMW specifies that the bolts used to mount the flex plate to the crankshaft are single-use, torque-to-yield bolts. They must be replaced whenever they are removed to ensure proper clamping force and prevent them from loosening over time.
Is any special programming required after replacing the flex plate?
No, the flex plate itself is a mechanical component and does not require any programming or calibration after installation. However, the technician will need to disconnect the battery and various electronic modules during the transmission removal process, which may require clearing fault codes from the system after reassembly.
Technical Specifications
OEM Part Numbers: 11-22-1-742-699 11221742699 1742699
Fits M73 and M73N 5.4L V12 engines. Includes integrated starter ring gear and incremental wheel for the engine speed sensor.
The information in this article is provided for general reference and educational purposes only. Vehicle specifications, procedures, and part compatibility can vary by production date, trim level, and region. Always consult your vehicle's factory service manual and verify part numbers before purchasing or performing repairs. Safety-critical components such as airbags, seat belts, and braking systems should be installed by a qualified professional.
- BMW 750i: