Rear differential / differential carrier / carrier....and loss of AWD

[bdubya]

Okay, my specific stupid noob question is just one of vocabulary - is the "rear differential" also called the rear "differential carrier" and/or the rear "carrier" (not axle carrier, just "carrier"). Do the three terms refer to the same part (which I would think of as the "rear differential", taking input from the propshaft and driving the axles shafts when needed)?

Reason I ask is, my '05 XC90 V8 AWD has been FWD for several months now (on snow or ice I can break the fronts loose pretty easily with DSTC disabled, but can't spin the rears at all, and if I put it up on stands and put it in gear, the fronts idle slowly but the rears don't move). Had it in to a local independent Volvo specialist, who diagnoses a failure of the "rear differential or Haldex clutch"; they can communicate with the DEM just fine and get no codes, the differential just isn't sending torque to the axles. So the natural fix appears to be to swap in a used differential, but when I go shopping on-line for one, I keep running into multiple terms for what sure looks to be the same part, and don't want to pull the trigger until I get this clarified.

[rattler]

Could it be the angle gear? Your symptoms sound a lot like it could be. Do the V8's have one? I have 2004 2.5t and have blown out the coupler twice and finnally stripped the input splines on the angle gear last time. It basically de-couples the rear wheels and makes lots of front wheel spin.

2004 XC90, 2.5T
204K and 46 US States.
-Brian

[hoonk]

but when I go shopping on-line for one, I keep running into multiple terms for what sure looks to be the same part, and don't want to pull the trigger until I get this clarified.

Why don't you let your "local independent Volvo Specialist" finish the diagnosis, find a new, used or rebuilt part, then give you a firm quote to fix it. (Yes there should be a diagnostic fee for that) - once you have more information you might be able to understand what is wrong with your car.

Then you could verify if they are charging a reasonable price to fix what they think is wrong. I wouldn't recommend "pulling the trigger" until you found out what is really wrong and what it would take to make it right again. If you are thinking of doing this yourself (and it needs a diff) a differential/sub frame replacement is not that difficult (just heavy/hard to manage parts) and could probably be done in your drive way if you were really ambitious.

- the rear differential has large gears and if something inside fails it's very noisy, the haldex clutch could go bad I guess, but usually it's the electronics, the DEM or pump (or both) goes bad - but you say there are no codes, and there always are codes when the DEM or pump fails.

The Carrier to me would be the rear sub frame that holds the rear differential, axles, springs, shocks, hubs, and brakes. If you are looking at used parts that is usually how that part of the car is removed. Cut the brake lines, undo or cut the e brake cables, unplug or cut the wiring to the abs sensors and DEM, undo the driveshaft, remove 6-10 bolts holding everything in and drop the sub frame to the floor. Put that in a pile with the rest of the sub frames and sell them as a unit or individual parts when needed.

Rattler suggested a bad coupler or angle gear, - easy to diagnose - does the driveshaft turn when the front wheels are turning? If yes angle gear and whatever coupler is used in a V8 is good (Angle gear and coupler failure happens on the the 5 cylinder cars)

[pbierre]

It's straightforward (car up on stands) to determine if the angle gear is stripped. When the angle gear is functioning, the propeller shaft is rotating in sync with the front wheels. If it is motionless while the fronts are spinning, then the angle gear is stripped.

If the propeller shaft is rotating but the rears are motionless, either the Haldex (AWD clutch) is inop, or (less likely) the rear axle differential is stripped.