A rear differential is also called the "rear end".  The only worry for the rear diff is scheduled replacement for its gear fluid.  If you do not know when the last time the fluid was changed, it doesn't hurt to change fluid now.  The rear diff contains the limited slip differential or LSD.

On a bad rear diff, you'll usually hear a lot of whining or grinding toward the rear of the car.  This noise gets louder as speed increases.  It is possible to rebuild these units, but it's easier (and cheaper) to swap in a good, used rear diff.

For differential fluid (viscosity) recommendations, check your owners manual or the Mazda FSM for more details.  We highly recommend using synthetic gear oil for your rear diff.
Click here for synthetic rear differential fluid recommendations!

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