DC shunt generators are used on FC-150 and FC-170 trucks. Early systems are 6 volt; later systems are 12 volt. All systems are negative ground.
The generator is an air cooled, two brush unit with non-adjustable output. The 6 volt unit is rated at 45 amps; the 12 volt unit is rated at 30 amps. If either the generator or regulator is replaced, the replacements must be matched for voltage and capacity, polarity and common manufacturer. If the components are mismatched, a loss of amperage capacity and/or damage to the generator will result.
The generator should be checked every 6,000 miles for damaged wiring, loose connections, brush length and brush spring tension. If new brushes are installed, they should be first sanded to provide as complete contact as possible with the commutator. Output should not be checked until the new brushes are completely seated. Brush spring tension is very important. High tension causes rapid brush and commutator wear; low tension causes arcing and low output. The tension can be checked with a pull scale. Tension for 6 volt units should be 35-53 oz.; 18-36 oz. for 12 volt units.
TESTING Generator Output Test
- Remove the armature and battery leads from the generator and connect a multitester between them.
- Remove the field lead from the regulator, and, while operating the engine at idle, touch the field lead to the regulator base. Increase the engine speed slowly, noting the charging rate.
Do not increase the output above the rated output of the generator.
- If the output does not increase as engine speed increases, check the wiring harness for shorts and open circuits. If the wiring is not at fault, the problem is in the generator.
Wiring Resistance Test
- Visually inspect the wiring and connections. Make sure that connections are clean and tight and the wiring is not cracked or brittle.
- Remove the lead from the regulator B terminal. Connect a multitester between this lead and the B terminal.
- Run the engine at about 1,500 rpm and turn on the lights and accessories until the ammeter scale shows a 10 amp charging rate. At this charging rate, note the voltage drop between the following points:
- Replace any wiring that does not meet these specifications.
REMOVAL & INSTALLATION
- Disconnect the battery ground.
- Remove and tag all generator wiring.
- Remove the adjusting bolt, loosen the mounting bolts and remove the belt.
- Support the generator with your hand and remove the mounting bolts. Lift the generator out.
- Installation is the reverse of removal. Make sure that the belt is properly tensioned. A 1 / 2 inch deflection of the belt at the mid-point of its longest straight run indicates proper belt tension.