2003-2004 INFINITI M45 Rear Upper Control Arm: Diagnosing Clunks and Finding Obsolete Parts
A complete guide to understanding, diagnosing, and replacing the increasingly rare rear upper control arms on your Y34 INFINITI M45.
- The most critical issue is part availability; new OEM arms are discontinued and aftermarket options are virtually non-existent.
- Symptoms of failure include rear-end clunking, a 'wandering' feeling when driving, and uneven tire wear.
- A used OEM part is the most practical solution; inspect it carefully for bushing integrity and any signs of bending.
- A professional wheel alignment is mandatory immediately after replacement to ensure vehicle safety and prevent tire damage.
Symptoms of a Failing Rear Upper Control Arm
When a rear upper control arm begins to fail, it's almost always due to the rubber bushings wearing out or the arm itself being bent from an impact. The symptoms can range from subtle noises to significant handling problems.
Clunking or Knocking Noises
This is the most common symptom. You may hear a clunking, popping, or creaking sound coming from the rear of the car, especially when driving over bumps, potholes, or uneven road surfaces. This noise is caused by excessive play in the worn bushings, allowing the metal parts of the arm to make contact with its mounting points on the frame or knuckle.
Unstable or Wandering Rear End
A worn rear upper control arm can make the car feel loose or unstable, particularly during turns or acceleration. You might feel the rear of the car 'steering' or swaying on its own. This happens because the arm can no longer hold the wheel at the correct angle, causing unwanted changes in suspension geometry under load.
Uneven Tire Wear
Because the upper control arm is a primary factor in setting the rear wheel's camber angle, a failure will cause the tire to tilt. This results in accelerated and uneven tire wear, typically on the inside or outside edge of the tread. If you see this pattern on your rear tires, a worn control arm is a likely suspect.
Visible Bushing Damage
A visual inspection can often confirm the problem. The rubber bushings located where the arm mounts to the subframe may be visibly cracked, torn, separated, or leaking fluid in some cases. Any visible deterioration is a clear sign that replacement is needed.
Known Issues, Recalls, and TSBs
For the 2003-2004 INFINITI M45, there are no specific recalls or Technical Service Bulletins (TSBs) issued by the NHTSA for the rear upper control arms. Searches for suspension-related recalls primarily show a major campaign for an inaccurate fuel gauge that could lead to stalling.
However, owners on forums report that the Y34 platform can be prone to suspension noises and wear over time. One owner specifically noted a "banging in the rear suspension" on an M45. The most significant issue for this part is not a defect, but its availability. Many OEM suspension components for the 2003-2004 M45, including the rear upper control arms, are now discontinued by Infiniti. This makes finding a replacement a major challenge.
Part Scarcity Warning: New OEM rear upper control arms for the 2003-2004 M45 are largely unavailable. Aftermarket support is also extremely limited, with most parts catalogs showing options only for the next-generation 2006+ M45. This makes sourcing a good-quality used OEM part the most viable option for most owners.
Buying a Used Rear Upper Control Arm
Given the scarcity of new parts, buying a used OEM control arm is often the only choice. Here’s what to look for to ensure you get a good part.
- Inspect the Bushings: The bushings are the most common failure point. Carefully inspect the rubber on both inner mounting points. Look for cracks, tears, dry rot, or any signs of the rubber separating from the metal sleeve. If the bushings look worn, you will likely have the same problem again soon.
- Check for Bends and Damage: Look down the length of the arm to ensure it is perfectly straight. Any bend, no matter how slight, indicates it was likely in an accident and will compromise your vehicle's alignment and safety. Check for deep gouges or cracks in the metal itself.
- Verify Part Numbers: Compatibility is key. Ensure the part you are buying matches the correct OEM number for your vehicle's side (left or right). The 2003-2004 M45 shares its platform with the 2002-2006 Infiniti Q45 (F50), and the control arms are often listed as compatible.
- Why Used OEM is a Good Choice: For a part like this with no good aftermarket support, a used OEM arm is superior to a non-existent cheap alternative. The original Infiniti parts were built to a high standard of fit and material quality. A used arm from a lower-mileage, non-corroded vehicle can provide many years of reliable service.
Cost Comparison for Replacement
The costs below are estimates. Prices can vary based on your location, the shop's labor rate, and part availability.
| Part/Service | Estimated Cost | Notes |
|---|---|---|
| New OEM Part | $400+ (If found) | Largely discontinued and extremely difficult to find new. Prices reflect new-old-stock if available. |
| New Aftermarket Part | N/A | No widely available aftermarket options were found for the 2003-2004 model year at the time of writing. Bushings may be sold separately. |
| Used OEM Part | $50 - $150 | The most common and cost-effective solution. Price depends on condition and source. |
| Shop Labor | $150 - $350 | Typically 1-2 hours of labor per side. |
| Wheel Alignment | $80 - $200 | Mandatory after replacing a control arm to ensure safety and prevent tire wear. |
| Total Estimated Cost (with Used Part) | $280 - $700 | Includes used part, labor, and alignment. |
Installation and Repair
Replacing a rear upper control arm is considered an intermediate-level DIY task. If you have experience with suspension work and the right tools, it is feasible. However, seized or rusted bolts can significantly increase the difficulty.
Difficulty Rating: 3 out of 5
Procedure Overview:
- Safely raise and support the rear of the vehicle and remove the wheel.
- Place a jack under the lower control arm to support the suspension.
- Unbolt the upper control arm from the top of the wheel knuckle.
- Unbolt the two mounting points connecting the control arm to the subframe.
- Maneuver the old arm out and install the new one.
- Torque all bolts to factory specifications.
Important: A wheel alignment from a professional shop is required immediately after replacing the control arm. Skipping this step will result in poor handling, unsafe driving characteristics, and rapid tire destruction.
Frequently Asked Questions (FAQ)
Is the left rear upper control arm the same as the right side?
No, they are not interchangeable. They are side-specific parts with unique part numbers. The right (passenger) side is 55501-AG00A, and the left (driver) side is 55502-AG00A.
Can I just replace the bushings instead of the whole control arm?
Possibly, but it may not be practical. While some aftermarket bushings might be available, pressing old bushings out and new ones in requires a hydraulic press and specialized tools. For most people, and even many shops, replacing the entire arm with a good used unit is faster, easier, and more cost-effective.
Do I need to replace the arms in pairs?
While not strictly required, it is often recommended. Suspension components wear at similar rates. If one side has failed due to age and mileage, the other side is likely not far behind. Replacing both at the same time can save you from having to do the job twice and pay for a second wheel alignment.
Will a control arm from a 2006 M45 fit my 2004 M45?
No. The 2006 M45 is a completely different generation (Y50) with a different chassis and suspension design. You must use a part specified for the 2003-2004 M45 (Y34) or the cross-compatible 2002-2006 Q45 (F50).
Technical Specifications
OEM Part Numbers: 55501-AG00A (Rear Right / Passenger Side) 55501-AG000 (Superseded by 55501-AG00A) 55502-AG00A (Rear Left / Driver Side) 55502-AG000 (Superseded by 55502-AG00A)
The control arm is a single, non-adjustable cast or stamped metal piece with integrated rubber bushings at the chassis mounting points and a single connection point for the wheel knuckle.
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.
- INFINITI M45:
- Symptoms of a Failing Rear Upper Control Arm
- Clunking or Knocking Noises
- Unstable or Wandering Rear End
- Uneven Tire Wear
- Visible Bushing Damage
- Known Issues, Recalls, and TSBs
- Buying a Used Rear Upper Control Arm
- Cost Comparison for Replacement
- Installation and Repair
- Frequently Asked Questions (FAQ)
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