F-150 differential noise


Old 12-21-05, 08:00 AM
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F-150 differential noise

I have a 2001 F-150 with the 3.55 limited slip differential. The differential makes a humming noise when you press the accelerator. There is no noise when coasting. The hum starts at about 25 mph and increases in pitch with increased speed. I changed the fluid to the recommended 75W140 synthetic with friction modifier. The old fluid was dirty but no metal filings. While I had the cover off the gears all look fine. The bearings feel good too. Does anyone have any ideas as to the cause of the humming noise? What needs to be replaced and at what cost? Thanks alot!
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Old 12-21-05, 11:32 AM
Join Date: Jan 2002
Location: Chicago
Posts: 1,915
I have a 89 Chevy G20 van that's been making this noise for the past 60,000 miles, and so far nothing "bad" has happened.

I'm not sure if the same noise on a FORD is as neglijable though.
Old 12-21-05, 05:45 PM
Join Date: Feb 2005
Posts: 579
From your description of the noise, you have a bad pinion bearing. Chances are there is fragments from that bearing floating around within the differential. The correct way to go about repairing this, is to replaced both pinion and carrier bearings. Also, clean the inside of the differential, including the axle tubes to verify there are no remaining fragments. While you have the axles out, it would be a good idea to repalce the axle bearings and seals.
If you know someone that knows how to set pinion depth, better call him up to save you some cash.

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