TM 10-3930-653-14&P Fig. 4-159.  Ground Test of Field Coil (3) BRUSHES AND BRUSH LEAD WIRE Check surface condition of brush contact and wear of   brush.      If   a   loose   contact   is   found,   it   should   be replaced. If brush is worn and its length is less than 11.5 mm (0.453 in), replace. Check connection of lead clip and lead wire. Check brush holders and spring clip to see that they are not deformed or bent, and will properly hold brushes against commutator. If brushes or brush holders are dirty, they should be cleaned. (4) BRUSH SPRING TENSION Check  brush  spring  tension  with  a  spring  scale  as shown  in  Fig.  7-11.    Replace  spring  if  tension  is  lower than specified value. Brush spring tension: More than 1.4 kg (3.1 lb) Fig. 4-160.  Inspecting Brush Spring Tension (5) ARMATURE ASSEMBLY Check     external     appearance of armature and commutator. (1) Measure  the  armature  shaft  for  any  bends  with  a dial  gauge.    Replace  armature   shaft   if   bend   exceeds specified value. Armature shaft bend: Less than 0.08 mm (0.0031 in) Fig. 4-161.  Inspecting Armature Shaft for Bend (2) Inspect  commutator.    If  surface  of  commutator  is rough,  it  must  be  sanded  lightly  with  a  No.    500  emery cloth.    Commutator   must   be   checked   also   for   out-of- roundness.    If  out-of-roundness  is  more  than  0.2  mm (0.008  in),  or  depth  of  insulating  mica  is  less  than  0.2 mm 4-97