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Jerry, Auto Mechanic
Category: Ford
Satisfied Customers: 2948
Experience:  Mechanic with over 30 years experience with N.Y.P.D. fleet service division
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2002 mercury mountaineer: the front differential..rear wheel..assembly

Resolved Question:

I have a 2002 mercury mountaineer. My mechanic tells me that I will need to replace the front differential very soon and probably the rear one before too much longer. He just replaced the right rear wheel bearing assembly. He believes that the damage to the differentials was caused by a mismatched set of tires. One of the four is 1" smaller in circumfrance than the other three tires. Could this be the cause of the damage to the differential. And how can i be sure that the differentials need to be replaced.
Submitted: 9 years ago.
Category: Ford
Expert:  Jerry replied 9 years ago.
Hello Mountaineer, Your mechanic is correct about the tires, they must all be the exact same size and condition. Any difference in diameter will cause the wheels to spin at a different speed and cause the differential to work against each other. The problem you would be feeling is a binding or lock up, when making turns at slow speeds, like a U turn in a parking lot. I would have the fluids drained and refilled with the correct gear oil, it may be best to purchase the oil from the dealer and get any additive that they recommend be added. This will usually stop this type condition. I hope this will help you with your truck ,thanks, Jerry.
Customer: replied 9 years ago.
Reply to Roadside Jerry's Post: But, how can I be sure that the differentials need to be replaced.
Expert:  Jerry replied 9 years ago.
Hi, If the problem is a chatter or locking feeling on turns and the fluid change and additive don't help, the differential unit would have to be overhauled. If the problem is a howling or whine type noise the while driving or coasting , the rear end bearings or gears are worn. The rear end would either have to be rebuilt, new bearings and/or gears replaced as needed.
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