I recently picked up a '99 F350 for a plow truck and have been changing the drivetrain fluids. This past weekend I did the rear differential, which is the Sterling 10.5" with 3.73 gears and a traction-lock. Ford says the 75w140 does not need to be changed unless the axle is submerged in water...I thought after 80,000 miles a change was in order. The oil looked pretty rough, and there was plenty of metallic paste (show in picture) on the fill plug and speed sensor. I collected a sample of the oil and sent it off for a UOA yesterday, I will share the results when available.
I also discovered that the differential cover was nearly rusted through. It looks like it got damaged at some point (hit a curb?) and rust started where the paint was missing. I ordered a “Rock Crusher” cover on ebay motors for $75 shipped; overkill for what I'm doing but it shouldn't rust out anytime soon.
Given the amount of crud in the axle housing I decided to refill it with "leftover" gear oil that I had sitting around the shop and drive the truck back and forth to work for a few days. I will use that gear oil as a “flush” and change it out with 75w140 next weekend. After looking at the local auto parts stores, I may have to order the 75w140; it seems that no one stocks more than a quart or two.
I also discovered that the differential cover was nearly rusted through. It looks like it got damaged at some point (hit a curb?) and rust started where the paint was missing. I ordered a “Rock Crusher” cover on ebay motors for $75 shipped; overkill for what I'm doing but it shouldn't rust out anytime soon.
Given the amount of crud in the axle housing I decided to refill it with "leftover" gear oil that I had sitting around the shop and drive the truck back and forth to work for a few days. I will use that gear oil as a “flush” and change it out with 75w140 next weekend. After looking at the local auto parts stores, I may have to order the 75w140; it seems that no one stocks more than a quart or two.
