Starter "flat spot" - what's causing this?

[Kneale Brownson]

I had a starter that "worked like a champ" when power was applied on the
bench, but couldn't muster any power to turn the engine over under load.
Before you reinstall it, I'd have someone check it under load.

At 04:07 PM 10/25/2005 +0000, radek at istar.ca wrote:
>Thanks guys!
>
>I took the starter out and counted the teeth on the flywheel:  lost track of 
>the number 
>but all are OK.  Next, I took the starter to the rebuilder who put it in a 
>vise and
>applied 
>power:  worked like a champ.
>
>I'm going to clean up all electrical connectors and the housing where it 
>attaches 
>to transmission, for good ground.  I'm also going to try to install some 
>sort of 
>heat shield on top of the starter to protect it from the exhaust manifold.  
>It sits
>directly 
>beneath and the original heat shield had rusted out a long time ago.
>  
>Hopefully, this will cure the problem.  Looks like it's not been getting 
>sufficient 
>amperage to operate, especially when hot (I understand the power draw will be 
>greater when the starter is hot).
>If all this doesn't help, it's rebuild time and it will be a different 
>rebuilder.
>
>Thank you for all for your help and support.
>
>Radek
>88 90Q
>91 V8Q 5-sp.
>
>> 
>> Message: 9
>> Date: Mon, 24 Oct 2005 01:23:25 -0400
>> From: Huw Powell <audi at humanspeakers.com>
>> Subject: Re: Starter "flat spot" - what's causing this?
>> To: Radek <radek at istar.ca>
>> Cc: quattro at audifans.com
>> Message-ID: <435C6FCD.4090004 at humanspeakers.com>
>> Content-Type: text/plain; charset=us-ascii; format=flowed
>> 
>> 
>> > For quite a few months now, my 1988 90Q has suffered from this
intermittent
>> > problem.  Sometimes the car starts like a champ, other times you turn the
>> > key and ... silence.   There is power draw (voltage drops) but nothing
>> > moves, clicks or otherwise.  Total silence.  Push start.
>> 
>> If it's truly silent but you get a power draw, it's almost certainly the 
>> starter.  In the meantime, the old trick is to whack it lightly with a 
>> hammer to see if it will work on the next try.
>> 
>> > As a note, I found one way of dealing with the issue:
>> > When the starter wouldn't work, I put the car into second gear and
rock it,
>> > trying to get the engine to rotate forward.  After such treatment it would
>> > often start. 
>> 
>> That might have had the "hammer" effect - or, if you don't get true 
>> silence but a click and whirring sound, you could be missing a few 
>> flywheel teeth, as suggested.
>> 
>> > However, a strange, grinding noise persists for a few seconds
>> > after the engine has started and then something disengages, everything
>> > returns to normal.
>> 
>> That could be the starter solenoid thing sticking and keeping on the 
>> flywheel after you release the key.
>> 
>> Prior to replacing the starter, I would use a test light on the starter 
>> trigger wire to make sure it's not the ignition switch at fault.
>> 
>> -- 
>> Huw Powell
>> 
>> http://www.humanspeakers.com/audi
>> 
>> http://www.humanthoughts.org/
>
>
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