1997-2001 Infiniti Q45 Flex Plate: Diagnosing Ticking Noises and Preventing Repeat Failures

Symptoms of a Failing Flex Plate

A failing flex plate can produce a range of symptoms, many of which can be easily misdiagnosed. The most common signs point to cracks developing in the plate, usually around the crankshaft hub or the torque converter bolt holes.

• Knocking or Ticking Noise: The most frequently reported symptom is a rhythmic knocking, ticking, or clattering sound coming from the lower engine area or bell housing (where the engine and transmission meet). This noise often changes with engine RPM and can sound very similar to a serious internal engine problem like a rod knock, leading to misdiagnosis. The sound may be most noticeable at idle or when the transmission is in Park or Neutral.
• Grinding or Scraping Sounds: If the flex plate is cracked or warped, it can make contact with other components. This can cause grinding noises when starting the engine or when shifting gears.
• Vibrations: A cracked or unbalanced flex plate will cause vibrations that can be felt through the floor or seats. These vibrations often get worse as engine speed increases.
• Starting Problems: If the teeth on the outer ring gear are broken or worn, the starter motor may struggle to engage. This can cause a whining or grinding sound when you try to start the car, or the engine may fail to crank over at all.
• Loss of Power: In cases of severe failure where the center of the flex plate breaks away from the outer ring, the connection between the engine and transmission is lost. The engine will rev up, but no power will be sent to the wheels.

Known Issues and Causes of Failure

While there are no specific recalls or Technical Service Bulletins (TSBs) for the flex plate on the 1997-2001 Q45, the most common cause of failure is well-documented across many vehicles. A cracked flex plate is often not the root problem, but a symptom of another issue.

Engine and Transmission Misalignment: The leading cause of repeat flex plate failure is misalignment between the engine and transmission. This can happen if the transmission was previously removed for service and not reinstalled correctly. Two small, hollow cylinders called dowel pins are used to precisely align the transmission housing to the engine block. If these dowel pins are missing or damaged, the transmission can be bolted on slightly crooked, putting constant stress on the flex plate and causing it to crack over time. Improperly or unevenly torqued bell housing bolts can also cause this issue.

Buying a Used 1997-2001 Q45 Flex Plate

A used OEM flex plate is often a better choice than a cheap aftermarket alternative. OEM parts are made to exact specifications for balance and material strength. Given the high cost of a new OEM part, a quality used one provides excellent value.

What to Inspect:

• Check for Cracks: This is the most important check. Carefully inspect the entire surface of the plate, paying close attention to the area around the central crankshaft bolt holes and the smaller torque converter bolt holes. Use a flashlight and look for hairline fractures.
• Inspect Ring Gear Teeth: Examine the teeth on the outer edge of the flex plate. Look for any that are chipped, excessively worn, or broken. Damaged teeth can cause starting issues and damage the starter motor.
• Check for Warping: Lay the flex plate on a flat surface to check for any warping or bending. A warped plate will cause vibrations and will fail prematurely.
• Examine Bolt Holes: Look for any elongation or damage to the bolt holes, which could indicate it was run with loose bolts.

Replacement Overview and Difficulty

Replacing the flex plate is a major repair that requires removing the entire transmission from the vehicle to gain access. This is not a task for a beginner or someone without a proper vehicle lift and transmission jack.

• Difficulty Rating: 5 out of 5
• Estimated Time: 6-9 hours
• DIY Feasible: Not recommended for most DIY mechanics due to the need for specialized equipment and the complexity of removing the transmission.

Key Torque Specs:

Proper torque is critical to prevent future failures. While you should always consult the factory service manual for your specific vehicle, common torque values are:

• Flex Plate to Crankshaft Bolts: Approximately 65 ft-lbs (88 N·m). Some sources suggest a torque-plus-angle procedure. Always use a star pattern when tightening.
• Torque Converter to Flex Plate Bolts: Approximately 38 ft-lbs (52 N·m). It is often recommended to use a thread-locking compound like blue Loctite on these bolts.

Cost Breakdown

The majority of the cost for this repair is labor due to the time it takes to remove and reinstall the transmission.

OEM Part Numbers

The 1997-2001 Infiniti Q45 uses the VH41DE engine. The following part numbers are associated with this vehicle, but be sure to verify fitment with the seller using your car's VIN.

• 12331-6P000: This is listed as the direct fit for the 1997-2001 Q45.
• 12331-87U00: This part number supersedes several older numbers, including those for the previous generation Q45 (12331-60U02, 12331-60U03), and may be used as a service replacement.
• 12331-60U02, 12331-60U03: These are primarily for the earlier 1993-1996 Q45 but have been superseded by 12331-87U00.

Frequently Asked Questions (FAQ)