How does this brake calliper securing nut arrangement work? This comes from a set of Weinmann Type 370 calliper brakes. The two nuts you see are normally firmly located inside the plastic hood, not as they are shown.

I think they are intended to function as some sort of self-locking/clutch system, so that the nuts don't work their way off, while still not preventing the callipers from moving.

In this particular case, I am not satisfied that the nuts are securing the callipers on the bolt as tightly as they should be. As I rotate the plastic hood, the nuts move down the bolt, but then further rotation doesn't tighten mechanism; the hood just rotates over the nuts instead of rotating them.

How is this actually supposed to work?



http://www.classiclightweights.co.uk/components/weinmann-components.html says:


  In the late '70s or early 1980s the domed centrebolt on the standard side-pull calipers was replaced by a plastic cover over two plain steel locknuts. These brakes were centred using an inverted allen key tool.


but that doesn't shed any light on the how the two-locknuts-in-a-plastic-hood arrangement is supposed to work.
IIRC, the cover slides off by pulling on it, the two locknuts are locked against each other to adjust the caliper play (usually with the goal of creating as little slop as possible with no binding of the arms), and then the cover is pushed over the two locknuts. I believe the idea is its got lots of little notches inside so it can grip both nuts at once, making it impossible for them to vibrate loose.