RE: Ur-q starting (not)

["Buchholz, Steven" <Steven.Buchholz@kla-tencor.com>]

> On occasion my 88 Ur quattro will refuse to start, usually at the most
> inconvenient times and places. Tends to be when trying to restart after a
> journey, the starter just appears to be completely dead, just 'clunks' but
> doesn't turn. It did it tonight in my drive after my trip home from work
> (25
> miles fairly fast so things were hot under the bonnet) and the only
> response
> to the key was a click from the starter solenoid. It started fine later.
> The
> starter is about 18 months old.
> Theories?
> Starter suffering heat soak?
> Some sort of ignition switch fault?
> 
... most likely is a combination of the above ...

When you replaced the starter did you refit a heat shield on the solenoid?
The older ur-q's came with the bigger starter and a metal heat shield that
covers the motor and solenoid ... I'm willing to bet that yours has the one
with the reduction gear and is smaller (like on the MC's here in the states
of the same vintage) ... these have an aluminium covered fibruous shield
that covers only the solenoid.  Many people don't know that the shield is
present and rebuilt starters (once again ... here in the states anyway)
don't seem to come with the shield attached.  If the solenoid gets hot
enough the actual force generated by the electromagnet and core is reduced
(what is it, the Miller Effect?) ... which may be a contributor to starting
problems.   The funny thing is that here in the states a new heat shield can
be obtained for less than US$5.  If you don't have one you'll need to get a
hose clamp that is large enough to go around the solenoid.  On my ur-q right
now I have a new-style starter with the ur-q metal heat shield -and- a
fibruous one ... hey I had them both around.  I had to rebend the big shield
to accomodate the smaller size of the starter motor ...

Over time the internal resistance of the connection from the battery through
the ignition switch to the starter solenoid (and the ground from the battery
to the starter perhaps) can increase to the point where a significant
voltage drop occurs between the battery and the starter solenoid.  This is
probably quite likely to be a contributor to your problem.  I think that VW
put out a tech bulletin that stated that if the voltage measured from the
solenoid hot lead to ground was less than 10 volts you could experience
starting problems.  On my '83 urq I found that the ground braid that went
from the left engine mount to the frame of the car had become brittle and
many of the individual wires had broken.  This would be most likely to have
an adverse effect at times when the alternator was trying to supply a lot of
current to the battery or when the starter was running ... and might not
affect normal operation so much (but may cause intermittent behaviour).  

So ... my recommendation to you is to check the condition of the ground
braid and check to see if you have a heat shield installed on the starter.
If all is well, then measure the voltage at the starter.  If it is below
spec you might want to consider adding a relay to the circuit so that the
starter switch will only have to provide enough current to close the relay
and you can get a better battery voltage for the solenoid right there at the
alternator terminals.  My problem was resolved by simply replacing the
starter and fitting a heat shield, but when I install my headlight relays I
plan to add a relay for the starter as well.  

HTH!
Steve Buchholz
San Jose, CA (USA)