2606 brake question

The old disks did not appear to be very worn. They were 7/16" thick and still had about 1/16" grooves on each side of both discs. The metal plate surfaces looked good with just some minor rust that I can sand off. The plates expand ok and the ball bearings inside look ok. The springs hold the plates tight together.

I inquired of the thickness of new brake discs and they are only a 1/2" thick which isn't enough difference to take up all the adjustment. My question is why did the brake adjusting ball loose all of its adjustment and need a spacer to work? The adjusting rod will only pull so far.

The only other thing I just thought of, but won't know till I look, is that the brake pedals on the shaft is missing a woodruff key or something but I believe only the left brake uses the shaft but the right brake has the same problem and the right brake is a direct pull on the adjusting rod so that can't be it.