In looking at post war commutators, there is typically arcing damage at the edges of the slots. The is most noticeable on whistle motors which only run in one direction. This might argue for a higher resistance brush. It may also explain why in later years Lionel used brushes with a reduced surface area. Post war motors ran with brushes with very low resistance. They were a mostly copper, which explains the copper tinge to the brush color. There were also brushes with copper plating. I have always assumed that was an effort to improve electrical contact between the brush tube and the brush. These would have a copper color. Some early brush tubes were silver plated, probably for the same reason. There was a design change in the 700E where Lionel went to brushes with shunts. The shunts were used in the 700E, the 763E, 701 and the 227 family of locomotives. Then the use of shunts was discontinued for over 70 years. It sure would be interesting to learn that story.
The information I have on the brush composition is as follows. Note that the accurate measurement of very low resistance is difficult. My guess is that Lionel determined the resistance of the brush by running a current through it , measured the voltage drop, and then calculated the resistance. This would let them check the resistance at the operating temperature of the brush.
OO1M-33, 71.8% copper, 28.2% carbon
1-92, 25.15% copper, 74.8% carbon, resistance .000588 ohms
226E-92, 71,8% copper,28.2% carbon, resistance .00019 ohms, .0005" copper plate
622-121 and 2020M-33, Morganite Co. Brush grade CM-3, .0005" copper plate
1001M-46, 1661E-29, and WS-110, 74.8% copper, 25.15% carbon, resistance .000358 ohms
622-202, 2055-12, 50-82 and 0500-101, composition #14
This information is just a snapshot in time. Things were always changing.
I try to run post war brushes in post was equipment. I believe that Lionel, during the post war era, had a good engineering department and took design details seriously. This may have also been true again for a little while when Lionel was in Detroit. Currently I think Lionel leaves many of the design details up to their contract manufactures.
I do not like to run the newer, mostly carbon, brushes because they are soft and wear quickly. The resulting carbon dust gets all over inside the motor. Maybe it is because I am use to working with much higher voltage motors, but I do not like conductive dust all over the insulating material. The brushes are functionally too soft if the commutator gets blacks streaks on it. I do not see the high copper brushes resulting in excess commutator wear. There does seem to be a lot of grooving, which I do not understand the reason for. But the grooves can be sanded out fairly easily leaving a flat smooth commutator service. The down side of this is that the commutator bars are fairly thin, maybe 18 gauge, so there are not a lot of refinishes in the commutator.
The method I use to sand the commutator keeps the commutator surface perpendicular to the armature shaft. Using this method I have noticed that some commutators have wobble in them. Not sure how much, but I would guess 5 to 10 thousandths. This means every time the armature revolves the brushes are forced up into the brush tube. Then as the armature continues to rotate the brushes come back down. While the brushes are accelerating down the spring tension will be reduced resulting in arcing. Sanding the commutator perpendicular to the armature shaft removes the wobble, but can take quite a bit of time.
My preference would be to stay away from high resistance and/or high carbon content brushes in post war equipment. I do not have enough experience with more modern equipment to express an opinion.
