Followup:  it turns out the culprit was the park/neutral starter
cutout switch.   It had slipped out of alignment and was making just
enough contact so that the van would only start when conditions were
just right.    Glad it wasn't my starter.

On Jul 10, 2006, at 11:23 AM, Michael Diehr wrote:

> My 85 vanagon has developed a problem where the engine won't crank at
> all when the starter battery voltage has dropped to about 1/2 charge
> or around 12.0 volts.   When you turn the key, there is a "click" and
> you can hear the voltage drop a little, but the starter doesn't move
> at all.  I've verified this behavior with two different batteries,
> and checked all the battery connections.
>
> Is this a known failure mode of the starter or starter solenoid?
>
> Thanks!