2002 Mustang, differential

My mechanic recommended differential change @53,000 miles?? then again @70,000. Does it need to be changed if it’s not leaking?

Do you mean differential oil? My mechanic has given me similar advice because he is not satisfied with the grade recommended by Ford.
What does your Service Manual say?

I normally do 80K between diff oil changes. That’s worked well for me for the past few decades. I’m sure you’ll get more opinions, but I’ve also heard that from others. I also run synthetics everywhere.

Like Fawad said, tho, what does your service manual say?

I think (?) the interval on differential oil is about 60k miles. Changing it at 53 and again at 70 is a bit of overkill it would seem to me.

If the car has a Posi rear axle then I’d change it more frequently than 60k miles.

My daughter has a Mustang and I’ve thumbed the manual on that one but I don’t remember for sure what the interval is.

The Ford spec is;
Synthetic rear axle lubricant does not need to be changed for the life of the vehicle ( normal service use ) unless axle service is required or submerged in water.
( non-synthetic fluid , 3000m/3months )

Your service intervals are in a book separate from the owner’s manual, “scheduled mainteinance guide”.
No books ? ( silly goose ,why’d you toss them out ? )
www.owner.ford.com
upper left menu choice “vehicle basics” select owner’s manual there to view pdf.

Wow, changing your differential fluid 3 months or 3K miles. You’ll sure have some clean, fresh pumpkin juice. I think that interval might be for engine oil, or maybe it is a typo?