Brass needs to be applied to a totally clean surface. I usually use an angle grinder and a cup brush to clean an area at least 1" wide all the way around the place I intend to braze, and get the metal hot enough to melt the brass rod by simply touching it to the red-hot workpiece. Use plenty of flux to assure a good bond to the base metal. The brass should flow smoothly over the surface it's being applied to and bond like solder does when it "tins" to an electrical connection. If the brass piles up on top of a repair, the base metal isn't hot enough. Once an initial bond is made, additional layers can be built up to strengthen the repair if desired.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
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