Help needed with a 2001 LX470 with 116k miles that started making noise during deceleration. I've read through forums and have tried to check the possible causes for the noise, and I think I've more or less isolated the problem to the front differential. The sound seems characteristic of a pinion bearing that lost preload (if there is loss of preload it's not so bad that I can feel it by wiggling the pinion flange). A description of the symptoms and what I've done so far is listed below. Would appreciate anyone's thoughts on whether this is enough data to incriminate the front diff. Is there anything else I should check or troubleshoot before spending the time/money on repairing the front diff?
Symptoms
Key Findings (pointing to the front of the vehicle as the source of the noise)
Road tested and investigated by two professionals
Completed activities (process of elimination to isolate the cause of the noise)
Symptoms
- Whirring sound (woo-woo-woo) only upon deceleration/coasting
- Sound remains with engine braking, shifting to neutral, and braking
- Sound goes away with gas/acceleration
- Sound frequency and volume matches vehicle speed (most notable at highway speeds)
- Sound seems to be coming from the front but it’s hard to tell
- No vibration is felt in the steering wheel
Key Findings (pointing to the front of the vehicle as the source of the noise)
- The sound is gone after removing the front drive shaft and driving with the center diff locked (i.e., rear wheel drive mode)
- The sound is present when the rear drive shaft is removed and driving with the center diff locked (i.e., front wheel drive mode)
Road tested and investigated by two professionals
- Differential specialist: could not guarantee sound was coming from the differentials nor isolate to either the front or rear diff
- General mechanic: suspected tires as cause of noise
Completed activities (process of elimination to isolate the cause of the noise)
- Removed the front and rear driveshafts and checked the differential pinion bearing for play by grabbing the pinion flange and pulling it in/out and rocking it side-to-side/up-and-down; no play was felt - no play was felt in the transfer case outputs either.
- Jacked up the front of the car and rotated the front wheels individually - no unusual noises or drag
- Balanced and inspected all tires - performed by Costco; noise is still present
- Swap out front tires, one at a time with spare tire; noise still present
- “12/6 position” check on all wheel bearings (front wheel bearings were serviced 3k miles ago)
- Inspected CV axle cir-clips; cir-clip is fully seated and no gapping to the CV axle observed
- Inspected for loose/rattling parts, like heat shields; nothing found to be loose
- Update: Inspected and greased front and rear drive shaft u-joints and slip shafts; u-joints felt smooth and did not feel any play (tested by hand only)
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