The first issue is in controlling which joint slides and which joint locks. The conventional approach would be to press the bushes into the roller ends, so the brass only slides on the steel shaft. However it might be tricky to get the shims tight enough in the roller ends, because it is difficult to press the bushes in with the shims wrapped around them - usually the shim slips as much on the bush as it does on the plastic roller, so you end up with the shim protruding at the end, and if you cut that off, only half the length of the bush is a tight fit in the roller ends. All that is a bit esoteric - it looks in the picture as if you've got the shim all the way in, somehow.
The other concern I have is metallurgical: what material are the roller ends made from? In the picture they look like aluminium. Aluminium and brass are incompatible: they set up a million little voltaic cells, and the aluminium part is the sacrificial anode, so the roller ends get eaten up fairly quickly.
All of this is resolvable, at least in part. If the roller ends are actually plastic rather than aluminium, the second issue doesn't arise. If they are aluminium, you should use aluminium bushes.
