I recently purchased an 80 amp upgrade kit for my original 42 amp series 10SI 1970 alternator. Kit included new brushes/springs, voltage regulator, stator, and diode trio.

Installed everything, put it on the car, and had no voltage output at the lug. Installed a delco replacement alternator on the car and had plenty of juice. OK, so the problem lies within the original upgraded alternator.

Took that 80 amp upgraded alternator to Autozone where they tested it on their machine which indicated bad diodes. So, I searched their GM database and found another application having 80 amp diodes ('79 caddy). Installed the new diodes right there while at Autozone, put it back on their machine and, sunnova-beach, bad diode indication AGAIN.

Here are my questions:

1) I reused the original rectifier bridge from the 42 amp original guts in the new 80 amp guts. I understand after reading the factory service manual that the rectifier also has diodes in it. Could this rectifier be my problem? Should I upgrade it to one that is rated for the 80 amp alternator?

2) New stator checks out ok. Could the rotor be bad?

3) I'm 99% certain I have all the insulating washers in the correct locations, but if I don't could that be my problem?

Somebody point me in the right direction. There aren't that many parts to troubleshoot, just thought someone could save me some time.

Thanks in advance.

The rec bridge has 6 diodes inside of it, and they are the diodes that a tester identifies. The other diode with three terminals on one side and one on the other is know as the light minder diode or diode trio, with a total of 3 doides inside. The bridge changes a/c current to d/c current.
Remove the bridge and trio from the alternator. Use a analog ohm meter or digital ohm meter set in diode test.
What you are going to do is test each diode by itself. Connecting a meter to one side of a diode should read current flow one way, and nothing the other way. If current flows both ways, or does not flow both ways, the diode is bad.

Touch one lead to the single long terminal on one side of the trio, and touch the each of the other three terminals on the other side of the trio. The one lead is common to all three diodes in the trio, the other three are the other end of each diode in the trio. All three should show no current or even current readings. Reverse the leads and what ever you got readings or not, should be reversed. If one of the three does not match either way, the trio is bad.
Now look at the bridge. There are or were 3 nuts on studs in the center of the bridge. With the nuts off, gently lift the metal tabs under the nuts, be sure the taps don't touch anything, inculding the base where they go in. Not touch the housing on one side of the bridge with one meter lead. Touch each of the three tabs, one at a time, with the other lead. Now reverse the leads and check again. Same as the trio. flow one way, not the other. Now check the three on the other side of the bridge. IF any of these fail, the entire bridge is bad.

If all diodes are good (total of 9) you need to look for another problem, insulators, stator, windings, etc.

There are three leads on the stator windings. Touch each combination of two with the meter and look for current flow. There is no need to test these in reverse. If all three are connected, check from one lead to the case of the stator. This should be open, or no flow.
Not touch the two slip rings on the rotor. You should have current flow, if so, touch one slip ring and the rotor housing, this should be open.

Touch the condenser inside the alternator, if it has one, at the wire lead and the housing. You may see a breif flow than nothing, or depending on your meter, nothing. Good. If you have flow, the condenser is shorted.

When you reinstall everything, touch the positive lead on the back of the alternator, which goes to the bridge, and touch the alternator case. This should be open, if not the lead is shorting on the case or the bridge is bad.
You have now tested everything inside the alternator except the regulator. If everything else is good, replace the regulator.

The only thing else is bearings. I'm guessing you already checked them before disassembly. Just hold the alternator in your hand and spin it. I should spin freely with no noise or roughness.

Thats everything. Good luck. Let me know how it works and feel free to and me again as you go.

Ken Styer

sorry for the typo, where it says not touch, it should say now touch.
Ken Styer

Ken:

Thanks for the troubleshooting procedures. I'll check everything as indicated and let you know what I come up with.

Again, much thanks.

Mike

ettev- Sorry to hijack your thread, but where did you get hold of the upgrade kit?
The 63A alternator on my 1980 has trouble keeping up, since the car had halogen headlights installed, and I assume they draw a lot more current than the old sealed beam units. Now its winter, if I'm driving with the headlights and rear defog going, the alternator just cannot keep the voltmeter needle above 13V, even when cruising around 3000 rpm.
I'd like to keep the original casing and just upgrade the guts. I assume the kit has a stator with more windings? Are there any heat issues you know of? Obviously a bigger output will bring more heat - does it need a better fan on the pulley?

I'm in the UK, so I'd be needing to look at mail order really. Thanks in advance and good luck with yours!

Since I have the factory in my '78. I'm going to send it out to get upgraded and have the casing cleaned for shows.