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Silver soldering will have, as awmawson suggests have annealed the wire. Alternatively, if you rapidly cooled the joint you will have embrittled it. Either course of action is fatal to the high carbon cold drawn steel wire that makes up a brake cable.
If you ever have to go down the route of terminating a cable using a non mechanical method then the end of the cable needs to be un ravelled for a very short distance and the resultant "brush" needs to be drawn into a conical cavity which can then be filled with low melting point metal such as soft solder.
With a small diameter cable tinning using a soldering iron rather than a flame is essential(a flame will inevitably anneal the odd single strand here and there)
Typically the depth of the conical cavity needs to be 5 times the cable diameter and the included angle of the cone would be around 15 degrees.
This is an over simplification of what is a method of cable termination that , for safety's sake needs to be tightly controlled.
As Lew says, got to an expert and pay.