[sonicj]

i can't think of a reason to hang on to the old brushes. if you have a lathe you can turn down the commutator to make it smooth again. if not, your local motor rebuilder or machine shop can likely turn down the comm for a few $$.

this is a example of a worn commutator. the upper area is what the comm should look like. the lower portion is obviously worn. torque is a function of current; fresh brushes on a freshly turned comm will make better contact and allow for more current to pass through the motor. ie: more torque. another thing to look for is to make sure the brushes are fully seated on the commutator. if the armature isn't pushed deep enough into the motor can, the brushes won't make full contact with the comm (since they are hanging off the end) and you will lose torque. ymmv.

i would like to see how you coupled the motor to the transmission/freewheel/cassette/whatever. is shifting gears out of the question?
-sj