I may try sawdust in the HO52, 4.11 differential in my 51, 3600. When I bought the first set of 4.11's I found last year I could see the ring gear was pitted but the clearances and bearings all seemed fine so I went with it. With a fill of Lucas it was acceptably quite around the house and trips to town. I did later add a small bottle of STP and it got a bit quieter.
Well, on last weeks 1,300 mile (round) trip to Luckenbach I learned that constant driving causes the Lucas/STP soup to break down, it becomes less viscous and the carrier howls like a banshee.
Since a new ring/pinion set is made from unobtanium I'm likely going to pick up another set of 4.11's and be a little more picky. Till then I'm thinking of trying this.
] Which is 250W gear oil.
For those that don't click on the link;
"PSC Swepco 203 Moly gear oil features the very finest quality base stocks, suspension-grade moly, and an exhaustively tested additive package which includes Lubium, Swepco's highly effective extreme-pressure/anti-oxidant additive. This unique combination provides the ultimate in protection for high temperature, heavy load, and extreme-service operation of most industrial gear boxes, manual transmissions, final drives and power take off units. For proven performance, use Swepco 203!"
Anyone been down this path and have comments? If so I'm definitely interested.