37-MT, 41-MT, and 42-MT Series Starting Motors Caterpillar

Note: The graphics that are illustrated in this section refer to the solenoids that are 24 VDC. Solenoids that are 12 VDC use the same procedure, but only one battery that is 12 VDC is used.

Table 1

Required Tools
Part Number	Description	Quantity
6V-7070	Digital Multimeter	1
225-8266	Ammeter Tool Gp	1
4C-4911	Battery Load Tester	1

Illustration 1	g00713118
Basic solenoid circuit

A basic four terminal starting motor solenoid circuit is shown in Illustration 1. The two windings that are found in the solenoid are the hold-in winding and the pull-in winding. The windings can be checked with the following procedures.

Hold-in Winding Test

Illustration 2	g00713128
Hold-in winding test

1. Refer to Illustration 2 in order to make the connections to the solenoid. Disconnect all other leads to the solenoid.

2. Close the switch. Observe the reading on the multimeter. Use the battery load tester to adjust the battery voltage until the correct voltage is obtained. Refer to Table 2.
   Show/hide table

   Table 2

   Voltage Specifications
   Model	Operating Voltage	Measured Voltage
   37-MT	12V	12V
   37-MT	24V	20V
   41-MT	12V	10V
   41-MT	24V	20V
   42-MT	12V	10V
   42-MT	24V	20V

3. Observe the reading on the clamp-on ammeter. Refer to Table 3 for the correct amperage.

   Note: A high reading indicates a shorted winding. A low reading indicates excessive resistance.

   Show/hide table

   Table 3

   Current Specifications
   Model	Operating Voltage	Measured Current
   37-MT	12V	23±2A
   37-MT	24V	6.75A max
   41-MT	12V	23.0A
   41-MT	24V	14.6A
   42-MT	12V	23.0A
   42-MT	24V	14.6A

4. The hold-in winding can also be checked by measuring the resistance. Disconnect the batteries. Select the "200 Ω" range on the multimeter. Connect one of the leads of the multimeter to the "S" terminal and connect the other lead to the "G" terminal. Refer to Table 4 for the correct resistance reading.
   Show/hide table

   Table 4

   Resistance Specifications
   Model	Operating Voltage	Measured Resistance
   37-MT	12V	.50 to .56Ω
   37-MT	24V	2.96 to 3.48Ω
   41-MT	12V	.50 to .59Ω
   41-MT	24V	1.37 to 1.77Ω
   42-MT	12V	.50 to .59Ω
   42-MT	24V	1.37 to 1.77Ω

5. Replace the solenoid if any of the above readings are incorrect.

Pull-in Winding Test

Illustration 3	g00713129
Pull-in winding test

1. Refer to Illustration 3 in order to make the connections to the solenoid. Disconnect all other leads to the solenoid.

2. Close the switch. Observe the reading on the multimeter. Use the battery load tester in order to adjust the battery voltage. Refer to Table 5 for the correct voltage.
   Show/hide table

   Table 5

   Voltage Specifications
   Model	Operating Voltage	Measured Voltage
   37-MT	12V	12V
   37-MT	24V	20V
   41-MT	12V	10V
   41-MT	24V	20V
   42-MT	12V	10V
   42-MT	24V	20V

3. Observe the reading on the clamp-on ammeter. Refer to Table 6 for the correct current value.

   Note: A high reading indicates a shorted winding. A low reading indicates excessive resistance. To avoid excessive heat, do not leave the switch closed for more than 10 seconds at a time. The current will decrease as the heat increases.

   Show/hide table

   Table 6

   Current Specifications
   Model	Operating Voltage	Measured Current
   37-MT	12V	36±2A
   37-MT	24V	89±5A
   41-MT	12V	56.5±4.5A
   41-MT	24V	92.5±7.5A
   42-MT	12V	56.5±4.5A
   42-MT	24V	92.5±7.5A

4. The pull-in winding can also be checked by measuring the resistance. Disconnect the batteries. Select the "200 Ω" range on the multimeter. Connect one of the leads of the multimeter to the "S" terminal and connect the other lead to the "Mtr" terminal. Refer to Table 7 for the correct resistance reading.
   Show/hide table

   Table 7

   Resistance Specifications
   Model	Operating Voltage	Measured Resistance
   37-MT	12V	.17 to .19Ω
   37-MT	24V	.64 to .70Ω
   41-MT	12V	.11 to .15Ω
   41-MT	24V	.43 to .49Ω
   42-MT	12V	.11 to .15Ω
   42-MT	24V	.43 to .49Ω

5. Replace the solenoid if any of the above readings are incorrect.