<VV> starter woes

[Padgett]

Hokay folks, things are getting a bit confused here. A GM starter is made 
up of two major components (and has not changed a whole lot since 1914), 
the starter motor and the solenoid.

When the solenoid fails, nothing happens (or maybe a click). Major failure 
mode after 40 years is a burned contact plate. The motor again has two 
major elements, the motor itself (armature, field coils, brushes, 
bearings). A rebuild usually consists of bearings and brushes though 
occasionally you will find a [shorted|open] armature or burned contacts on 
the armature. The other element in the motor assembly is the bendix drive 
in the "drive end". This unit slides on a splined end of the armature.

On starting the solenoid pulls a stirrup assembly which moves the drive 
from the disengaged position into contact with the ring gear on the 
flywheel. Once fully pulled out and the gear is engaged, a contact is made 
in the bottom of the solenoid that energises the motor. As long as the 
motor is trying to spin faster than the engine, a set of dog clutches 
(rollers) connect the motor to the flywheel. and the starter spins the motor.

To avoid spinning the starter at a speed greater than reasonable for an 
unbalanced assembly with smal plain bearings, when the motor stars, the dog 
clutches disengage, and the starter is not longer directly connected to the 
flywheel.

When the rollers get worn, they no longer engage properly and may only turn 
the engine for a second or two before slipping. This is when you hear the 
starter speed up without turning the engine. This is more likely to happen 
when the bendix is hot and it heats up quickly in use.

In general, the bendix drive is available as a separate  part however the 
difficulty of removing a starter means that typically a general overall 
inspection will be made and brushes, bearings, and solenoid will be 
replaced along with the drive since the starter has to be disassembled (at 
least the nose piece removed) to replace the drive.

More than you wanted to know ?

Padgett