Mazda CX-9 This larger SUV adds a V6 option, as well as more cargo room, to the CX-7 option.

Hum from rear differential

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Old 07-21-2022, 03:41 AM
Ryan80's Avatar
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Location: Indiana
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Default Hum from rear differential

Hello,

I'm chasing a hum on our 2014 cx9 AWD touring. The vehicle has about 160000 miles on it. The hum starts to become noticable in the cabin at about 30 mph and gets louder as vehicle speed increases. There are no drivability issues. No shakes or vibrations.

​​​​​​At first I thought it was a wheel bearing but that doesn't seem to be the case. With the vehicle supported I was able to verify that the hum is coming from the rear differential. It looks like I have a little leak on one of the shaft seals. The diff bushings seem to be ok. They do show some cracking when you force them to flex, but the rubber is still soft and they are intact. I changed the oil in the diff. It was clean and the magnet had nothing abnormal on it.

My gut is telling me that the side bearing on the side with the leak is the culprit, but I'm not sure how best to verify this without dropping the diff. If the bearing is my issue, am I better off to replace the bearing, or the entire diff? I'd just like some input on what to expect if I try to repair the diff. I found some used diffs on good old eBay for a couple of hundred bucks but that option has its own concerns. Any advice or input is appreciated.
 
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