Alternator Mystery Part

[Sebs]

Hello all,

I have a 1984 Porsche 911 and have been having some electrical issues. Things like the battery not holding a charge and the engine suddenly stopping while I'm driving it.

I checked the battery voltage with a DMM with the car running at 2000 RPM. The voltage started at around 12.5v but I watched at it slowly climbed higher and higher. I shut the car off after it got up past 17v.

This seems to point to a faulty regulator.

I should also mention the alternator light does not come on at all, either with the ignition on and the car off or with the engine running.

I took the alternator out and here is where I'm puzzled.

Looking at the regulator brushes, they look like they have plenty of life left. However, from the photo, you can see the Blue spade connector coming from the regulator looks burned. Especially when compared with the Yellow spade connector from the other side, which is clear and looks clean.

The other issue is the part the Blue spade connector was attached to. The metal connection is very rusted and broke off when I tried disconnecting the Blue connector.

What is this rectangular plastic part? Is this something that is replaceable? Could this be the cause of the issues I've been having?

I appreciate any insight anyone may have on this issue.

Thanks!

[reclino]

That part is your diode trio, its looking pretty fried. See the below site for a good breakdown of the parts in this alternator.
Tiedemann Auto-Elektrik

When I rebuilt mine I was able to order slip rings, brushes, and other assorted parts from
https://www.aspwholesale.com/index.php?_a=category&cat_id=16
they did not have the diode trio
I ordered Japanese Nachi bearings from Amazon
front bearing 6303-2NSE
rear bearing 6201-2NSE

David

[DRACO A5OG]

17v? Really?

Time for a rebuild/swap

You should have your battery tested as it may have damaged cells now.

Welcome aboard!

[rick-l]

reclino - thanks for the link to the alternator parts.


There must be a place to get slip rings for an 88 alternator but I haven't found it.

[Sebs]

reclino, thank you for the links and the part name.

It sounds like the voltage regulator went bad, and burned out the diode trio.

Since your post, I've done some searches, but can't seem to find a diode trio as a single replacement part. Do they come as part of the rectifier? The preview images of rectifiers I've found don't show a diode trio attached. Could they be internal in newer parts?

DRACO, you mentioned rebuilding/swapping. Would replacing the regulator (and diode) not be enough to fix the alternator issues? Could there be other, underlying issues that could cause the regulator to go bad? If so, how could I check for those?

[patz]

Best to have a qualified re-builder go thru it. Remans are known to fail out of the box or soon afterwards.

With a re-builder you can talk face to face and have someone to yell at as opposed to an unknown.

[DRACO A5OG]

Originally Posted by Sebs

DRACO, you mentioned rebuilding/swapping. Would replacing the regulator (and diode) not be enough to fix the alternator issues? Could there be other, underlying issues that could cause the regulator to go bad? If so, how could I check for those?

Take a look at the Voltage Regulator's bushes.

Have the alternator rebuilt or replace a warrantied replacement, as mentioned they do fail out of the box. Ask us how we know

[Sebs]

Darn, I was hoping to fix it myself, but it seems like in cases like mine, where something has failed, the only way to be 100% sure it's fixed is to either replace it or have it rebuilt by someone who knows how to do it properly.