Actually, I reread the OP, and noticed that these were hydraulic, and deleted my post. It's still possible that these are some sort of brake force limiters, but I don't know the specific details of these brakes and can't say for sure.

I suspect that if there's any kind of adjustment of both ends, then they are a variable volume chamber and used to fine tune the pad clearance. If there's no ability to adjust anything, then they're probably a force limiter.

If they are a force limiter, I suspect that if cut open, we might find a piece of slightly soft elastomer, which would compress as the surrounding oil pressure increased.