Good Morning:
As the title says, I've got a question regarding the 2009 AWD system, but please allow me a moment of venting about the overall frustration of this situation.
I'm an entry level, professional mechanic. Although still inexperienced with many things regarding drive train systems, the basic, mechanical principles of operation are not a mystery to me. But sometimes the most obvious answers are right in front of us and we need someone else to point them out. That said, here's a shorter version of a long story:
A few years ago, my wife and I were looking at a 2009 AWD (2.4L) with just under 90K miles. It was in very good condition. On the test drive, I did notice a slight vibration from the rear end, but based on the sound, I thought it was a heat shield or something body-related and didn't give it its due concern, and we bought the car.
About 20K miles later, the vibration had gotten worse and is clearly related to the drive train as it changes depending on the speed and engine load. I found the rear most u-joint on the drive shaft had dried out and was "rough" when moved by hand. Since the u-joints are stamped in place, I had no way to replace them (I talked to a local shop that specializes in drive shafts and axles and they couldn't do anything with it) and installed a replacement drive shaft from a junk yard with good u-joints in it.
That didn't fix the vibration.
Just for the sake of exploration, I pulled the viscous clutch off the front of the differential and found that the bearing that supports the clutch coil (electromagnet) had been almost completely shredded. Since the metal shavings from that had destroyed the pinion seal, I decided it was best to rebuild the differential since there was most likely bearing damage inside the case.
I found a replacement bearing for the clutch coil at a local bearing supplier and got the remaining parts for the rebuild from the dealer.
Fast forward a couple years later, and that oh-so-identifiable vibration is back.
Here's my question: WHY is there a clutch coil in the viscous clutch? When looking back to earlier AWD models (compare with a 2006, for example), that clutch coil isn't there.
I've been doing a lot of research in trying to figure out why the clutch coil was added - I was hoping to find a TSB, recall or other info on earlier models stating something to the effect of "the AWD systems were having this issue, we think adding a clutch coil will solve it" but no such luck. I haven't been able to find anything more than generic info from GM on the 2009 system.
When you look at how the drive train is set up, the drive shaft hooks to the viscous clutch and the VC is splined directly to the drive pinion - there doesn't seem to be any practical purpose for the clutch coil to be there.
Can somebody please explain the purpose for this?
Thank you.