I detected a noise in my rear diff last week. 2021 CX-5 GT AWD, 124,000 miles. I had changed all fluids at purchase ~65k miles using Amsoil products. The car had been a rental before I bought it. After that first fluid change, I saw an oil residue on the housing on subsequent trips under the car for other tasks, so I checked it at every motor oil change just to be sure it wasn't running dry. I could not find a crack mentioned in another thread, nor any seepage from a seal. I cleaned and continued to monitor. I might have overfilled, resulting in some fluid coming out of the breather. Anyway, I did another change at 124k after hearing the noise and there were lots of shiny flakes on the magnet. Looks like a bearing is going. We have recently purchased a small camper (2,500 lbs) but have only pulled it maybe 200 miles so far. Otherwise, my tow bar has only been used for a bike rack. I don't typically engage the parking brake unless I park on an incline, which is infrequent.



Does anyone rebuild these, or just plug and play with a new units?
What is the expected lead time for one, or are they readily available in the US? I see one on realmazdaparts.com
What is the reliability of the viscous coupling? That's an expensive piece! Just curious.

 

Not sure I'd mess with a used or rebuilt, but others here may say otherwise.
A new rear differential is around $850 and they are usually in stock at most online Mazda parts dealers,
The viscous coupling on the other hand is as you say expensive, around $1200.
Parts is parts, generally you get better ones from better manufactures but that isn't a 100% statement.
Should it last as long as your vehicle yes, but then the OEM one should still be good at 124,000 miles.
Which means, if maintenance is done properly and the vehicle isn't beat on...it still all comes down to the luck of the draw.

 

Thank you for your input.
After further research, it is not common practice to rebuild these units. I did find a new one at the price point you mentioned. Prices are all over the place, from $850 to $1600. It pays to keep shopping around and enter the VIN at each site for a match.

 

Yep generally these ones don't seem to get rebuilt. It's either new or trying used if you can find one. If it's going to be a long term vehicle I'd bite the bullet and go new.