BOLT 8T7505 - Caterpillar

The brushes are located at the back of the armature on the following graphics. On some starting motors, the brushes are at the front of the armature. The electrical operation for the starting motor is consistent for all starting motors. The graphics are for the 12 Volt starting motor.General Information
Illustration 1 g00584068
Rest Position (1) Armature reduction gear (2) Armature (3) Field winding (4) Brushes (5) Idler reduction gear (6) Overrunning clutch gear (7) Pinion (8) Overrunning clutch (9) Solenoid contacts (10) Plunger (11) Return spring (12) Hold-in winding (13) Solenoid (14) Pull-in winding (15) Key start switch (16) BatteryA DC Series wound motor is used as the starting motor. The starting motor has a field winding (3) and armature (2). The excitation and armature windings are connected in series. The armature drives overrunning clutch (8) through gears (1), (5) and (6). The end of the solenoid (13) has splines for the overrunning clutch (8). The solenoid is an integral part of the starting motor. The solenoid pushes the overrunning clutch (8) with pinion (7) toward the flywheel ring gear. The end of plunger (10) is a spool which is connected to the overrunning clutch through splines. Return spring (11) helps return the overrunning clutch to the rest position after the key start switch (15) is released and solenoid contacts (9) are opened. Overrunning clutch (8) protects armature (2) from an overspeed condition. The clutch also allows a smooth engagement of pinion (7) into the flywheel ring gear. The overrunning clutch is held on the splines of the solenoid. The reduction gears will reduce the speed of the pinion. The speed of pinion (7) is reduced by 25 percent to 33 percent of the armature. Operation
Illustration 2 g00584084
(1) Armature reduction gear (2) Armature (3) Field winding (4) Brushes (5) Idler reduction gear (6) Overrunning clutch gear. (7) Pinion (8) Overrunning clutch (9) Solenoid contacts (10) Plunger (11) Return spring (12) Hold-in winding (13) Solenoid (14) Pull-in winding (15) Key start switch (16) BatteryWhen switch (15) is closed, battery current will flow in two directions. Current flows from battery (16) to switch (15). The current from the battery flows through the pull-in winding (14), field winding (3), armature (2), brushes (4), and ground. Current also flows through hold-in winding (12) to ground. The activation of pull-in winding (14) and hold-in winding (12) produces a magnetic force. The force that is produced pulls plunger (10) to the left. This moves clutch (8) and pinion (7) toward the flywheel ring gear.
Illustration 3 g00584092
The Solenoid Contacts Closed. (1) Armature reduction gear (2) Armature (3) Field winding (4) Brushes (5) Idler reduction gear (6) Overrunning clutch gear (7) Pinion (8) Overrunning clutch (9) Solenoid contacts (10) Plunger (11) Return spring (12) Hold-in winding (13) Solenoid (14) Pull-in winding (15) Key start switch (16) BatteryWhen plunger (10) is pulled to the left, solenoid contacts (9) close. At this point, pinion (7) is close to meshing with the flywheel ring gear. When this happens, pull-in