Can you clarify what you're trying to do? How and why are you trying to lock something to put a drum on?

when putting on the new rear brake shoes, there is a small bar (horizonally) across the top that holds the shoes to the wheel cyclinder with two springs. There is a small catch on it that keeps the shoes to gether until you have put the brake drum on. When you step on the brakes it should expand the brakes to release the catch, but it is not doing this. I would think that the car would have to be running in order for the power booster to apply pressure to release this catch. Maybe the power booster is leaking and not enough pressure to actually expand the brakes?

Any chance you can post a closeup photo of the assembly?