I split my Ruckstell this afternoon and these pieces dropped out. Is this the babbitt thrust washer? The Ruckstell axle was fitted sometime in the 70s and has the large brake drums. I thought the babbitt thrust washer was only used in the early model Ts.
Yes, it's the sorry remains of a Ford thrust washer.
Babbitt thrust washers were used in most Model T's, at least 1915-27. The thrust washer material seems to be a different more crack prone babbitt formula (lead?) than what's in the engine bearings.
In the Ruckstell there's a bearing on the LH side that takes the side load from the pinion/crown wheel so the only Ford thrust washer would be on the less loaded RH side of the differential. Still best to use a repro bronze washer there.
That's a familiar sight. Here's my version of your picture.
An original babbitt washer.
A later bronze washer. The ones currently available have the grooves straight across like the originals.