Columbia ParCar Expediter EX21-24A, Service Manual

Page: 87 / 94

Section 10 – Traction Drive System
ARMATURE TESTING
Before the armature is reassembled into the motor, the
following test should be performed.
1. Check armature for grounded circuits by placing one test
lead of a Dielectric Breakdown Tester, also referred to as a
“growler”, on the commutator and other lead at armature
shaft. The ground test light should not f ash. A flash
indicates failed insulation between core and armature
wiring. See Figure10-11.
2. For short circuit connection, use a hacksaw blade to locate
any shorted windings. Rotate armature slowly in growler
jaws and hold a hacksaw blade in parallel against top of
armature. The steel blade will be attached to the core and
will vibrate when two shorted armature coils are located.
See Figure 10-12.
BRUSHES
Brushes should be inspected for uneven wear and signs of
overheating, such as discolored brush leads and brush springs.
Check brush box for physical damage. Make sure brush holders
are not loose on the brush box assembly. See
Figure 10-9.
Check brush for correct clearance and freedom of
movement in the holder.
New brush length:
1.20” (30.5 mm)
Minimum brush length:
0.60” (15.2 mm)
Rep
lacement brush length: less than 0.60” (15.2 mm) If any
brushes are worn to the point that replacement is necessary, the
complete brush set should be replaced. Never replace just one
pair of brushes. Do not substitute brushes. The brushes are
matched to the motor type and application to provide the best
service. Substituting brushes of the wrong grade can cause
commutator damage or excessive brush wear.
BRUSH SPRINGS
Check the brush springs for correct alignment on the brush. A
brush spring that does not apply equal pressure on the center of
the brush will cause the brush to wear unevenly.
Use the following procedure for checking brushes for
proper tension. See Figure 10-13.
1. Place paper strip between brush face and commutator.
Figure 10 - 6
Figure 10 - 7