Mercedes-Benz W123 starter motor faults
Why does the W123 starter not turn but only click or stay completely silent?
The cause is usually worn brushes or a faulty solenoid (the starter motor's engagement relay). Poor connections at the battery terminals or the wires to the starter, as well as a loose earth, cause the same symptom, so check them first.
Why does the W123 starter turn slowly or spin freely?
Slow cranking is usually caused by worn brushes, worn armature bushes, oxidised wires or a loose winding. If the starter spins but the engine does not turn, the fault is in the bendix (the gear's freewheel clutch). Tapping with a hammer may help for a moment but does not fix the fault.
How do I overhaul the W123 starter?
The starter comes off with two bolts. The gaps between the commutator segments are cleaned and the brushes checked. The solenoid plunger and cylinder are cleaned. If the armature and bushes are worn, it is worth renewing the brushes, solenoid and bendix as well.
Why does the W123 starter not have the strength to turn the engine in frost?
Dirty or thick grease stiffens in the cold, and the bendix spring may be worn. Worn armature and bushes are a common cause. Dismantling, cleaning the commutator, greasing and a new bendix help. Also check the battery charge and the wires of the starter and the alternator.