quattro Digest, Vol 79, Issue 18

[Tom Leppke-Hennig]

>
> Message: 2
> Date: Sat, 15 May 2010 17:35:42 -0400
> From: Cody Forbes <cody at 5000tq.com>
> Subject: Voltage reg?
> To: quattro at audifans.com
> Message-ID: <43A1FA88-ECF5-4AFF-89AE-32B4D59E7658 at 5000tq.com>
> Content-Type: text/plain;	charset=us-ascii;	format=flowed;	delsp=yes
>
> I haven't seen a failure mode quite like this before so I shal employ
> the collective wisdom. Seems like a voltage regulator failing, but
> could maybe be bigger.
>
> So I'm cruising down the road in my '87 5ktq taking the family to the
> mall. At one point I noticed the tach fluctuate a little. Not quite
> like the old bouncing tach syndrome, just a lazy ~300rpm occillation
> while the engine was definately steady. I pulled up the volt meter in
> the climate control head and noticed that we were down to 10.3v. I
> immediately turned off the A/C and the voltage came quickly up to
> about 12.5v. This car has never been a great charger for the 4 years
> I've known it and two that Ive owned it, usually 12.8-13.0 daytime and
> low 12's at night with lights and everything going. Anyways, when I
> stopped at the next light the voltage very quickly rose to 14.0v with
> the engine at idle. As soon as I raised the revs to pull away it
> dropped back to 12.5v. We were more than halfway to our destination so
> I decided to motor on. On the highway voltage fluctuated 12.3-12.9.
> Back off the highway I noticed the voltage fluctuating with the
> cooling fan as it should, but it was swinging from about 12.3 with the
> fan on to near 13.8 when it turned off.
>
> -Cody (mobile)
>


Cody,

Someone else hinted at it. The failure usually attributed to the voltage
regulator is actually the brushes. They are integral to the VR. I
personally have never had a 'bad' VR from an electronic standpoint other
than they tend to run about .5V less that I think they should. Many on
this list have talked about how to replace just the brushes. There is also
plenty of information out there about how to trick the VR into running a
bit higher with a diode placed somewhere or other. I never bother as I
haven't been able to find replacement brushes. I just buy a new regulator.

Everything you describe is right in line with the way they act with worn
out brushes. There is a stop in there to prevent the brushes from grinding
all the way down to the spring, so while they are in the transition phase
between still good and worn out, they act utterly unpredictably. I pull
the alternator every other VR change and put new bearings in it as well,
but you can get away without that if they aren't howling.

Finally, I have found that the Taiwanese knockoff VR available at on of
the FLAPS actually seems to run at the correct voltage, but has a steel
cover and steel (!) contacts that rust here in salt country, so I have to
grease the shite out of it and inspect it every year.

Have fun

Tom LH