I'm not sure, Stuart. I do know the fluid in the rear end is really dirty and gritty as well. I was reading the shop manual and it talks about a 12-bolt rear end for a 3/4 ton. Mine has 10 bolts, but guess that is immaterial to the issue at hand. I read about how to pull the axles and am wondering if I pull the rear cover plate and the axles if that will give me sufficient access to clean everything up. I'm not sure if everything will fall apart inside once the cover plate is pulled or not, having never done this before. I wonder if pumping some cleaning solvent through the axle shaft after pulling the axles will flush everything back to the differential and then drain out with the rear cover plate off? And then hit the axle shafts with air from my compressor. I don't want to use any type of solvent that will damage seals etc. I am guessing that there is no seal at the end of the axle shaft where it goes into the differential since I believe the axles get their lubrication from the differential itself. I was checking Patrick's catalog looking at higher speed rear ends and I don't see one offered for the 3/4 ton. I was kind of thinking about putting in a higher speed rear end after going through all of the trouble of tearing things apart, but doesn't look like there is one for a 3/4. Again, this grinding noise wasn't happening when I first drove it. Back when I had the vibration problem, the grinding wasn't happening. So although I have driven it no more than maybe 3-4 miles total since I fixed the vibration, I suppose that could have been long enough to circulate the gear lube and pick up all of the sand. I don't think the grinding is coming from the transmission either. The sound I'm hearing is very similar to grinding of gears when you miss a gear, but it isn;t happening during shifting but more like during decelleration from a speed of about 30-40. Doesn't do it at low speed. Nor does it do it during acceleration. I had thought about trying to drive through it to see if putting a few miles on it would fix the problem, but now that I've seen the condition of the gear lube, I need to fix that first.
