Is the alternator going bad?

DAVES89 · September 29th, 2007

Lately I have had my battery light flicker on/off. I went to the gauge screen on my '89 and watch the wild fluctuation of my volt gauge. It will go from 12.6 to 15.9 and points in between. Sometimes it will set itself and lock in at 14. Last night was the first time it acted up while the headlights were on and the lights would "pulsate" as the volts would change so fast. The pulsing would stop when it would lock in at 14 and start again if/when it started changing amps again. The battery is a relativly new one. It is 750 amps/630 cold crank amps.

Ronnie · September 29th, 2007

I would bet on the alternator, or more specifically the built in voltage regulator. Here locally we have an automotive electrical shop that will repair the alternator or sell the individual parts. I bought the parts and rebuilt mine for about $40. That included new bearings, brushes and a new regulator ($10.87). Autozone wanted over $100 for a re-manufactured.

The alternators on the Reatta are relatively easy to rebuild. The brushes just clip in and no soldering is needed (at least on mine). Just take a little care in taking it apart to avoid breaking the brushes or brush holder. You have to work the rear case from side to side to get the brushes to clear the slip rings.

harry yarnell · September 29th, 2007

There is a tiny hole in the rear housing where you can insert a nail (or other suitable instrument)to hold the brushes in their keeper while assembling the housings together. Then you pull the nail out, and the brushes spring onto the slip rings...

Tinker · September 29th, 2007

DAVES89,
In case you would like to tackle this job yourself, here is a VIDEO FROM YOUTUBE that will show you how to do it. There are two parts to the video, each about 10 minutes long.
Personally, I think this guy is a little "Ham Fisted" doing this job and he does miss a couple of minor things (like checking the rotor for internal grounding) but other than that he is pretty thorough. Also, this is not a Reatta alternator but, it is GM and the procedure is 99% the same.
Part 2 is the better video, it shows you what Harry is talking about when he mentions using the tiny hole to hold the brushes in place during reassembly.
By the way, I think all you need is a new set of brushes. You can check everything else while you have it apart.

Have fun!!!

DAVES89 · October 2nd, 2007

Because I was out at the local u-pick yard, I grabbed a alternator. Runs great except for the bearing noise. So my question is, do I leave the one with the loud bearing in or do I put back the original one and deal with the voltage fluctuation? Until I get back to the u-pick yard to swap out?

Mike_s · October 2nd, 2007

Guess it depends on how loud the bearing is.

I had an alternator with a noisy bearing but the voltages looked fine, besides the noise it ran ok for a few hundred miles until it quickly went into screach mode, stopped outputing power which stalled the car at 45mph in traffic, started smoking and was going snap, crackel, pop untill I was able to disconnect the battery.

In regards to the other one, With the voltage regulator failing and the voltage bouncing around I think your taking the chance of frying a lot of $$ electronics.

Ronnie · October 2nd, 2007

I would rebuild the one with the bad bearing as soon as possible. I would only install the front and rear bearings and the brushes if they are worn down. It appears the electronics in the one with the bad bearing are good so you won't have to change regulator or rectifier diodes unless you just want to for piece of mind. It would cost you very little money and would be quicker than going back to the junk yard. That way you would know you had an alternator that was going to last for a while.

Barney Eaton · October 2nd, 2007

Since alternators are fairly easy to install, Why don't you take the "new" one and install it to see if the voltage problem goes away. Then you can decide which one you want to rebuild. You could take the regulator from the new one and put it in the old one and you will have no additional cost.

GM had a problem with altenators used on the 3.8 and 3800 in the '80's with overheating and they would fry. Sometime around 1988 or 1989 they open up the back for more airflow and the problems went away.

TommyH · October 2nd, 2007

I had a similar problem. The car eventually died in the middle of the street, randomy. Got a new one, all was better!

DAVES89 · October 3rd, 2007

Thanks for all your advice. This am before heading out I swapped the front of the good bearing alternator to the back end of the good regulator/brush alternator to make one good one. The voltage is stable and everything works fine. Thanks for the heads up on the video, it gave me the confidence I needed, as I never took one apart before and could only envision parts falling out with no idea how to put them back..