4-37. EXCITER-AUXILIARY GENERATOR BRUSHES AND BRUSH HOLDERS (cont)
Adjust brush holder carbon box to within 1/8 inch (3.2 mm) of the commutator. Use a 1/8-inch (3.2 mm) sheet of
fiber for a gage. Tighten clamping block bolt (10).
Check the thickness of brush (9) in brush holder (13). Side clearance of brush should be approximately 0.004 to
0.010 inch (0.1 to 0.254 mm). Brushes with side clearance in excess of 0.010 inch (0.254 mm) will rattle, chip, or
break and must be replaced.
Try to maintain brush holders with equal spring
pressure. Unequal pressure will cause unequal
current distribution in the brushes.
Adjust spring tension as follows:
Attach spring scale to each spring (8) directly over brush (9) and pull straight up in line with the brush travel until
spring just lifts clear of the brush. The correct spring pressure is between 2-1/4 and 2-1/2 lb (1.02 and 1.14 kg)
for auxiliary end and between 1-1/4 and 1-1/2 lb (0.57 and 0.68 kg) for exciter end.
If the spring pressure is not in tolerance, replace brush holder (13).
11. Start locomotive in accordance with paragraphs 2-10 and 2-11. Apply soft stone to commutator and run
locomotive at half speed (no load) until the commutator is polished and brushes are seated.
Position cover (4) and install three flat washers (3), lockwashers (2), and screws (1).