Bottom Line Up Front: If you are seeing excessive metal shavings on the front diff drain plug magnet and in the gear oil when you drain it, I strongly recommend you have the front diff checked.
Here's the story: I bought my 2007 AC 4cy/5spd/4x4 in May 2010 with 23k miles on it.
In March 2011, at 42K miles I changed all my drive train fluids to synthetic (front and rear diff/xfer case/manual trans).
- I noted at that time that there were as much or more metal shavings on the front diff drain plug magnet as the rear diff.
Towards the end of November 2011, after our first big snowfall, I noticed quite a bit of noise coming from the front diff the first time I used 4Hi at hwy speeds.
- I changed out the front diff gear oil, and again noticed a lot of metal shavings on the drain plug magnet and in the used oil. After changing out the gear oil, things seemed to quiet down.
- But some of the noise still seemed to be there, and as I had been planning to change out the front wheel bearings in the Spring, I went ahead and changed out the wheel bearings on both sides. When I broke open the old driver side bearing, I noticed what appeared to be light brown scorching on the racer. When I put it all back together, it seemed noticeably quieter. I assumed the low hum noise I was hearing at that point, was "normal" drive train noise in 4Hi. I now know I was wrong.
- Around Christmas a tell tale circle about silver dollar size appeared on my Garage floor. When I crawled under the truck it was clearly coming from the back side of the front diff. When I had changed the oil in Nov, I didn't notice any leakage or seepage, but I didn't look real close either. I did it with the truck on jack stands and just enough room to get under and change out the oil. Since the plugs are on the driver side, the back section of the diff is partially blocked by the frame. I suspect the seal may have been seeping at that time, and I just missed it.
Please note the technicians words on the attached invoice, "Found excessive metal shavings in differential fluid. Recommend new front differential."
I was lucky that spot showed up on the garage floor before I crossed the magic 60K powertrain warranty expiration! Front diff is a $2200 job!
The front end is now quieter than it has ever been in the time I've owned the truck; both in 2Hi and 4Hi. I suspect there were issues in the front diff when I changed out the oil at 41K. I'll be interested to see how the front diff oil looks when I change in another 20K. At the rate I'm putting on the miles, that'll be around next Oct/Nov.
If the "sometimers" doesn't get me , I'll try to remember to post the results then.
Felt this was worth sharing here!