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Ok a little dispute with me and a buddy of mine . I am working on a 70 350/350 I bought from original owner . It’s some what a project but the car runs strong . The car has low mileage 32k on it and the PO said he never changed the diff oil or the gear oil .. The car shifts perfect and not a sound from the rear . My buddy says change it . I say it’s not necessary . Would love to hear your thoughts
When I bought my '72 I had no knowledge of its maintenance history. In my mind changing all the fluids gave me a known starting point for future reference. Additionally, it gave me a good excuse to get under the car and examine the gearbox and differential up close.
I know this may open a large can of “Worms.” What oil and additive do you as a rebuilder recommend for our old stock differentials. Does the case cover have to be removed to see if there is sludge buildup like the one in your photos. If it needs cleaning, can the differential be cleaned while on the car? Many thanks
Eli
The diff in the picture was bad, I have seen and worked on worse. Once they are at that level, the only way to clean them is to take them apart. If you go that far then replacing the common parts and addressing the weak areas is recommended. However, I know guys that would take it apart, clean it, and put it back together without changing anything but the cover gasket.
All comes down to what you want for your car = ok, good, or the best.
As for oil, I use Lucas 85-140 non synthetic gear oil and 2 bottles of GM limited slip additive. A big thing is how the posi is built, most times sloppy with the spring pack. If tight with the spring pack it will chatter. Clutch type is important. solid steels, snowflakes, fiber. Some are junk, some are good. Both are still being sold today.
The diff in the picture was bad, I have seen and worked on worse. Once they are at that level, the only way to clean them is to take them apart. If you go that far then replacing the common parts and addressing the weak areas is recommended. However, I know guys that would take it apart, clean it, and put it back together without changing anything but the cover gasket.
All comes down to what you want for your car = ok, good, or the best.
As for oil, I use Lucas 85-140 non synthetic gear oil and 2 bottles of GM limited slip additive. A big thing is how the posi is built, most times sloppy with the spring pack. If tight with the spring pack it will chatter. Clutch type is important. solid steels, snowflakes, fiber. Some are junk, some are good. Both are still being sold today.
Diff and gear oil change
