Owner's Problem Description
The owner of a 1995 Subaru Legacy reports a new noise after replacing the axle and CV joint. The noise is described as pulsating and may vary with speed. They have previously replaced the axle and CV joint but are unsure if the installation was correct. The vehicle currently has no warning lights, but the owner is concerned about the noise and its implications for safety.
Professional Technical Analysis
This 1995 Subaru Legacy is experiencing a pulsating noise following a recent axle and CV joint replacement. The vehicle is equipped with a 2.2L flat-four engine and an automatic transmission, with an estimated mileage of approximately 180,000 miles. The noise is most noticeable when driving, particularly during acceleration and deceleration, suggesting a possible issue with the installation or related components. Given the history of axle replacement, potential causes include improper installation of the axle leading to misalignment, bearing damage during installation, or issues with the CV joint itself. The pulsation may also be symptomatic of a faulty wheel bearing or a warped brake rotor. It's crucial to assess the interconnection of these systems; for example, a damaged wheel bearing can cause misalignment of the axle, leading to abnormal wear and noise. Additionally, the brake rotor condition must be verified, as a warped rotor can create pulsation felt through the brake pedal and vehicle body. Safety concerns arise if the noise indicates potential failure of critical components, which may lead to loss of vehicle control. This Legacy's current condition necessitates a thorough inspection of the axle installation, wheel bearing integrity, and brake rotor condition, ensuring all components are operating within their specified parameters.
Possible Causes
Most common causes (ordered by frequency):
- Improper Axle Installation: If the axle was not seated correctly during installation, it could lead to misalignment, causing abnormal noise. The torque specifications for the axle nut should be adhered to, typically around 150 lb-ft. Additionally, any damage to the CV joint during installation can result in noise and vibration. Signs include visible wear or damage to the boot or joint itself. - Pulsating noise during acceleration, visual inspection may reveal misalignment, signs of wear on the CV joint boot, and improper torque on axle nut.
- Wheel Bearing Failure: The wheel bearings are critical to smooth rotation and alignment of the wheel assembly. If the axle was removed and reinstalled, there is a chance the bearings were damaged during this process. Typical failure modes include excessive play or grinding noises, indicating the bearing may need replacement. The correct bearing preload should be checked, typically between 0.001-0.005 inches. - Noise increases with speed, possible grinding or humming noise, play in the wheel assembly when checked manually.
- Warped Brake Rotor: If the brake rotor is warped, it can lead to pulsation felt through the brake pedal and can create noise during wheel rotation. The rotor should be checked for runout, typical specifications allow for a maximum of 0.002 inches. If found warped, resurfacing or replacement is necessary. - Pulsation felt in the brake pedal during braking, visual inspection of rotor surface may show scoring or uneven wear.
Diagnostic Steps
Professional Diagnosis Process
Follow these systematic steps to accurately diagnose the issue. Each step builds on the previous one to ensure accurate diagnosis.
- STEP 1 - Visual Inspection: Begin with a thorough visual inspection of the axle installation, ensuring it is properly seated in the hub and any retaining clips are intact. Check for signs of damage on the CV joint boot and inspect the wheel hub for any abnormalities. Verify the torque on the axle nut is approximately 150 lb-ft to ensure proper assembly.
- STEP 2 - Test Drive Assessment: Conduct a test drive to replicate the noise under different driving conditions. Pay attention to the frequency of the pulsating noise during acceleration, deceleration, and turning. This can help narrow down whether it is related to axle installation, bearing failure, or brake issues.
- STEP 3 - Component Checks: Use a dial indicator to measure rotor runout and check for wheel bearing play by checking for excessive movement of the wheel hub when rocked back and forth. If necessary, disassemble the brake components to inspect the rotor and bearings more closely.
- STEP 4 - Torque and Preload Verification: Confirm the torque settings for the axle nut and verify the correct bearing preload settings between 0.001-0.005 inches. Adjust as necessary and reassemble components to ensure all settings are within specifications.
