I recently changed the rear diff fluid on my 1999 F250 Super Duty (180k) It was due plus I was getting some chattering when making turns from a stop. The Diff fluid had about 60k miles on it and seemed to be a little low even though I don't see any leaks. I paid to have it done last time so I can't say what kind of a job they did.

I used Motorcraft diff fluid and 8oz of friction modifier. Two weeks later and about 500 miles, today I noticed on two occasions when turning a moaning sound coming from the rear of the truck. Could this be a sign of too much friction modifier and the cluthes are slipping or is something else going on?

 

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