Almost. The bad connection has to be on the battery side of the solenoid.
If it is the solenoid contacts that are bad the motor can run slowly (or not
at all and just give a 'clonk') but the system voltage, and hence the
voltage operating the solenoid, is actually *higher* than normal, because
less current is being drawn than normal. A bad connection adds resistance
to the circuit which causes a higher than normal volt-drop when the load of
the motor itself is applied to the circuit. When this volt-drop occurs
between the battery and the solenoid the voltage at the solenoid can drop
below its hold-in voltage, so it drops out, which removes the load of the
motor, which reduces the current through the circuit, which reduces the
volt-drop, which increases the voltage across the solenoid, so it operates
again etc. This can happen with bad connections in the battery ground
circuit or the 12v circuit between battery and solenoid. In theory it
should also happen if the engine/gearbox ground-strap is bad, but in
practice there are usually enough alternative ground paths through the
heater, choke and throttle control cables to stop the solenoid dropping out
although the starter still doesn't get enough power to crank normally. It
also knackers said cables. Chattering can also occur if there are bad
connections in the 12v feed through the ignition switch (early cars) or
starter relay (later cars) to the solenoid operate terminal. In this case
even the 'normal' volt-drop in the main circuit when the starter is
energised can be enough to drop the voltage at the solenoid to below its
hold-in value. This is also a symptom of the solenoid on the way out, and
is not unknown, particularly on V8s.
PaulH.
----- Original Message -----
> 1. A bad battery connection or corroded inner solenoid contact limits
> the amount of current the system can carry.
>
> 2. When the starter is actuated, the solenoid activates and connects the
> starter windings to the 12v+.
>
> 3. This drops the limited current so much that there is no longer enough
> energy to keep the solenoid actuated, so the connection drops out.
|