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I noticed that the right backing plate on my M100 has 7 mounting holes. The left one has 6 holes that mount the plate to the axle flange. The hole in the backing plate looks factory made and the right side axle flange does not have a corresponding hole.

Does anybody know what purpose this additional hole could serve?

Thanks!

Hello Tom

I would say you have what started out as rear backing plate from a M38 or M38A1 on one side of your M100. The seventh hole is not a mounting hole but a drain hole. see TM 9-8012 page 247. I believe the hole is to allow axle oil to drain clear without fouling the brake shoes in the event of a seal failure.