There is a tool to hold the brushes back for assembly.
You can make a similar tool by taking any narrow piece of spring steel, banding or sheet metal and bend it into a long "U' shape. The open end of the "U" holds the brushes while you slide the armature together. As for removing the pinion, there are 2 types. One type in held on with a roll pin that has to be driven out with a punch. The other type is held on with a C-clip on the end of the shaft above the gear. The C-clip type is very challanging without the proper tools.
Rick
April 2006