2009 XC90 (3.2L) Rear Differential Replacement

[Flyredcat1]

My 2009 XC90 has a loud humming noise that has been diagnosed as a bad rear differential. There is no leak whatsoever. Car has 110K miles. Repair shop is offering a replacement from a 191K mile car with no warranty. Ugh. Does anyone know where a more reliable replacement might be found? Or does anyone rebuild these? Or car it be repaired? Thank you!

[precopster]

My 2009 XC90 has a loud humming noise that has been diagnosed as a bad rear differential. There is no leak whatsoever. Car has 110K miles. Repair shop is offering a replacement from a 191K mile car with no warranty. Ugh. Does anyone know where a more reliable replacement might be found? Or does anyone rebuild these? Or car it be repaired? Thank you!

It is indeed very rare for a rear differential to fail, especially given that these vehicles hardly perform true AWD at most times, with most of the torque bias at the front. There is a rear driveshaft carrier bearing that can play up. My money is on this.

[Flyredcat1]

Thank you! I will have my mechanics check this out before diving into differential replacement.

[ggleavitt]

One reference- https://www.swedespeed.com/threads/rear ... ne.219929/ , there are a few more on the internet.

Pinion bearing failure is not that uncommon, there are rebuild kits available with a few write-ups and there are range Range Rover techs familiar with the repair (rear diff is shared with Rover and Ford, it's in the link).

For sure check the carrier bearing as noted above but if that's in decent shape it might be worth a closer look back at the differential.

[ylwgto]

Dealing with this myself on my '09 XC90 R type (failing pinion bearing...whining noise) and recently purchased a used diff assembly from a 2008 v8 AWD.

I looked up specs for the 2008 V8 AWD (donor car) vs. 2009 3.2 R type AWD (my car) and am noticing that all aspects of the transmission and post-engine drivetrain are identical EXCEPT the "final drive axle ratio", with is different only on the R-Design (4.06 vs. 3.33).

2008 V8 2009 3.2 R
First Gear Ratio (:1) 4.15 First Gear Ratio (:1) 4.15
Sixth Gear Ratio (:1) 0.67 Sixth Gear Ratio (:1) 0.67
Transfer Case Gear Ratio (:1), Low - TBD - Transfer Case Gear Ratio (:1), Low - TBD -
Trans Description Cont. Automatic, Trans Description Cont. Automatic,
Fourth Gear Ratio (:1) 1.16 Fourth Gear Ratio (:1) 1.16
Final Drive Axle Ratio (:1) 3.33 Final Drive Axle Ratio (:1) 4.06
Trans Order Code NA Trans Order Code NA
Second Gear Ratio (:1) 2.37 Second Gear Ratio (:1) 2.37
Reverse Ratio (:1) - TBD - Reverse Ratio (:1) - TBD -
Trans Description Cont. Again Geartronic Trans Description Cont. Again Geartronic
Fifth Gear Ratio (:1) 0.86 Fifth Gear Ratio (:1) 0.86
Transfer Case Gear Ratio (:1), High 1.00 Transfer Case Gear Ratio (:1), High 1.00
Trans Type 6 Trans Type 6
Third Gear Ratio (:1) 1.56 Third Gear Ratio (:1) 1.56

Does the rear diff have to match the front transfer case ratio (like on 4x4s)? I assume the R-Type has a slightly higher ratio to help with "acceleration" off the line, which I do not need, but did I screw myself over here? I'd hate to install a unit that doesn't match the front transfer case ratio and mess things up. If all god, I'd actually appreciate the slight improvement in gas mileage a lower axle diff ratio may get me.