fwiw ....
I don't even 'believe in' bad solenoids on bosch starters.
I have never actually encountered one, not that making sure the plunger
isn't all goo-ed up isn't a smart thing to do if one is going to remove
their starter and take it apart for inspection, cleaning and a touch of
psychic healing.

The solenoid is not the weak area. The electrical path through the
solenoid depends on conductivity through the brushes and commutator I
believe. And that's the area  I think of when the hammer trick makes it
work one more time..
tired brushes, commutator segments, and bushings.

    The armature itself ....those can just get faulty eventually.
Nothing you can do about it   if that happens..
Electrical rebuilder shops can check them.

remove, disassemble, inspect, clean, get way into the small details of
your starter ..
sometimes that will help for sure.

On 7/25/2012 5:32 AM, craig cowan wrote:
> I was always of the impression it was a wearing solenoid when smacking
> fixed the problem.
>
> I have this same issue intermittently with my syncro. It sucks.
>
> -Craig
>
> On 7/25/12, David Bjorkman <ddbjorkman@verizon.net> wrote:
>> Are you saying the problem is with the solenoid and not brushes wearing
>> out?  I was under the impression that having to whack the starter was
>> because the carbon blocks were getting hung up or worn out.
>> What do you think?
>>
>> Dave B.
>>
>>
>> On 07/24/12, Aaron<a.robinson.lists@GMAIL.COM> wrote:
>>
>> I've been able to use the gear lever while turning the key. I'd turn key
>> with left hand and hold it in the start position while moving the shifter
>> from 1 to 2 quickly. That was be enough to loosen then solenoid. I
>> eventually I removed the starter, then cleaned up the solenoid and it is
>> still fine 10 years later.
>>
>> On Jul 24, 2012, at 9:15 AM, Mike wrote:
>>
>>> When I had to occasionally whack the starter on my '85, I used a
>>> broomstick through the wheelwell. Didn't have to get dirty that way and
>>> it worked perfectly.
>>>
>>> Mike