HiOSilver said:
Can someone help me understand what I have? I have a 2004 Envoy XUV with 4WD. I was under the impression that the front differential turns all the time - meaning there are no wheel locks or disconnects.
You and I and trailblazers have selectable 4WD systems. The OP has an AWD with a slightly different system.
On ours:
1) The
passenger side CV shaft has a disconnect on the right side of the oil pan to disconnect the CV shaft from the intermediate shaft that goes through the oil pan to the differential. This slightly helps you get better mileage because the differential won't totally spool up and back-drive the front driveshaft that adds a bit of friction to the system.
2) The
driver's side CV shaft is always connected to the front differential, so parts of the diff spin at all times (the end gears and spider gears) That's why it's important to keep up regular diff servicing even if you never use 4WD.
3) The front driveshaft from the transfer case to the front diff will not spin in 2WD mode because the transfer case clutches are not engaged.
4) But many other parts of the transfer case *do* spin in 2WD mode, which is why it's important to keep up with regular transfer case fluid change intervals, which is a surprisingly short 50K mile interval.
5) I've posted many times before about why A4WD mode is damaging to the transfer case clutches and it only helps poor drivers in marginal traction conditions. In certain less rare conditions, the shock of A4WD engagement can break you loose and CAUSE accidents.
