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Hi all, I recently rebuilt the diffs of the 870C I am restoring.
The front one is smooth like new, but unfortunately the rear is quite gritty, due to wear of the ring plates.
I already chose the less worn sides to be mated with the balls, but the previous owner already swapped sides, so both are worn.
I imagine that finding replacements for those plates is really difficult now, so I ask you: what can I do?
Shall I try to rework the worn plates to restore the surface finish? If so how?
I don't want to definitely ruin those plates..
Bye!

Use some really fine wet n dry sandpaper (1000 grit is good) and place it on top of a piece of glass (glass tables tops are great for this). Choose the diff ring side which is the least worn and work on it. Use some light oil and start lapping in a figure eight motion. No need to polish up the diff ring just enough to remove the worn areas (if anything leave the sand marks on the diff plates). This will work with the trust rings as well. Once satisfied the worn areas have been removed.....rebuild the diff with brand new diff balls on the pulley and also new trust bearings (this is critical).

If the diff rings are too badly worn this trick will not work but will be better than it was.