I changed the rear differential fluid in my 2003 this past weekend, and I was surprised to find that the old stuff looked like mud. I've changed a lot of differentials in my time and this is, by far, the worst stuff I've ever seen coming out.



The outside of the cover was pretty rusty (common issue with these trucks I believe). I was surprised to find that the top half of the INSIDE of the diff cover was also pretty badly rusted.

Some history on this rig...
I know it was originally ordered and purchased by a dock builder. I'm guessing that the rear of the truck spent a fair amount of time backed into lakes, etc. So it's not a stretch to say that water got inside the rear pumpkin. The dealer I bought it from told me at the time of purchase that it had basically been parked at the back of his lot for 2 years. So, water + 2 years = rust.

What I thought would be an hour long job turned into close to a four hour job. I spent a lot of time with the wire brush and cleaned everything out with brake cleaner. Followed by a thorough drying with compressed air. There were small bits and pieces of rust in the bottom baffle type areas of the differential which I was sure to remove. I inspected the gears closely and found no damage. And they've never been noisy in the time I've owned it. So I hope to have dodged a bullet.

Front differential will be next weekend. I hope it's not as bad.

 

Shame on you! But I'd say it's normal considering the age, also the rear end is vented to the atmosphere allowing moisture to enter the oil.

 

That's some nasty stuff