My understanding is that the "sabot" was a kind of shoe. In English, there is a proverb "to throw a monkey wrench, into something," i.e. to "sabotage" it. Could there be a French proverb that uses a "sabot" as a version of a "monkey wrench"?
Another possibility comes from Wikipedia, where a sabot is a projectile, which makes more sense, but which doesn't quite square with what I know of the word having been introduced around the time of the Industrial Revolution.