Hey guys,

I'm trying to track down a metallic scraping noises that I get when I let off throttle while still in gear. I figured it might be the differential so I'm going to replace that, the pinion bearings, and set the preload. Anyway, while I was preparing for that I spotted these scrapes on the interior of the trans. However there is no indication of there being any part on the other side of the case that would cause this because the gears on the other side don't seem damaged. Any thoughts?? You can also see that there are metal shavings in the case but they've welded themselves in place which is interesting...

 

Don't see the scrapes you mention. As a casting the diff housing can had casting flashing ground away. These could look like scraping. The metal shavings look to be casting related.The casting mold sand as some surface porosity and the molten metal flowed into porosity and well, those little bumps are the result.

Any real metal to metal contact would have the oil filled with a lot of tiny metal particles. If the housing is aluminum the diff fluid would look be an awful dark brown/black color with aluminum metal flake. If iron running a magnet through the fluid would have the magnet loaded with fine ferrous metal particles.

 

When I drained the diff fluid it was definitely dark brown. I drove it another 500 miles with redline in it which is pinkish yellow and it came up brown ish again. Taking a flashlight to the drain pan i could see it shimmer pretty good, but everything was very very fine no big chunks. The magnet which sits in the bottom of the trans has some buildup of really fine flakes on it as well. The scraping is noted in the pictures on the raised areas where the gears sit in the bearings on the transmission bell housing cover and on the perimeter of the concavity where the differential sits.