This question must have been asked before, but my search results turned up nothing. Does anybody know why the Bob Drake repro wheel cylinders have only 3 drilled and tapped holes but the backing plates have 4 available mounting holes? There is a tab on the cylinders for a 4th bolt but its not drilled and tapped for some reason. There looks to be plenty enough meat there to drill and tap for the 4th which is what i'll probably do, but there must be a reason why its not done from new. Were original Ford ones the same? Anyone? Thanks.
The backing plates all start life as the same stamping...rears get an extra hole punched afterwards to tale the E-brake cable. After assembly they were marked for position on the car (LF, for instance) presumably for assembly line to get the in the right place, since shoes and cylinders are not symmetrical. The four cylinders have stepped bores, big and little diameters, so also have to be in correct location...the 3 holes don't actually mandate correct placement, since there are 4 holes in plate, but at least mechanic can see where there's still paint around a hole! With handedness, front and rear, and orientation of input hole all 4 are different.