A few days ago while driving my 2.5L(DIS) ‘87 Fiero, the alternator light came on. I put a voltmeter across the battery and it showed about 11 volts when the engine was running, and about 12 volts when it was turned off. I figured the alternator needed some kind of servicing.

This is the first alternator I've ever had to remove from BELOW a car. After I got it out and removed the stator(?) assembly, I discovered that the insides were nothing like the alternator pictured in my Haynes manual. I was hoping that it would be something simple like replacing the brushes, but they appear to be fine. It also appears to be impossible to get at the internal regulator, etc, because there is a round plastic plate in the way that will not come out unless the field(?) is removed. But I can't remove the field because it is attached by three wires to the regulator(?) which is held in place by screws behind the plastic plate. You (hopefully) get the picture.

Anyway, is there anyone familiar with this alternator (6F) who could shed some light on how to get it completely apart and/or to check the rest of the internal components?

Or should I just say the heck with it and get another alternator? (I hate replacing anything that's possible to fix.)

Or is there something else other than the alternator I should be checking?

Any and all replies will be appreciated. Thanks.

Here's what I usually do when I have charging problems. Clean and inspect the battery cables and check all the alternator wires to make sure the connections are tight. Recharge the battery and have it load tested. If the battery and wires checks out ok then remove the alternator and have it tested. Several auto parts stores will test these for free. If your battery is not real old and since your charging light came on, you were probably correct in assuming the problem is in the alternator. A common problem with the newer style alternators (besides brushes) is the diode burning out, which I think has something to do with the internal regulator. Most automotive electrical shops can rebuild alternators. I personally don't mess with that, I buy a rebuilt one and recycle the old one by turning it in as a core to be rebuilt. Less headaches that way as far as I'm concerned. Hopefully, someone else will add more stuff to this discussion in case I omitted something.

Thanks for the response batboy. It's been a few years, but I've been able to get alternators working in the past by replacing diodes(?). (It's been so long, I've forgotten what I did.) All I can remember is that the parts cost about $4, which was a big saving compared to buying a rebuilt alternator! I just checked the price today and it was $118(Cdn). From the wrecker they're about $45(Cdn).

The problem with this style alternator is that even if I knew which internal component was faulty, I can't seem to figure out how to remove this round plastic plate which is in the way. It appears that the field windings were attached by their three wires from the outside through an opening (using crimp connections) AFTER everything was put into place. To anyone who is familiar with this alternator, I think you would know what I'm talking about, whereas to everyone else, what I'm trying to describe probably sounds pretty confusing. I should also mention that this alternator is the one that uses a serpentine belt.(‘87-‘88)

So, is there an alternator expert out there?

Sounds like a foreign car problem,I would try and locate one at a parts store,then start cutting wires to try and get inside,only if the bearings are still in good shape,otherwise,it may not be worth it.
If you remember,the function of the diodes is to flow energy in one direction only,so,if they're isolated,you should be able to test with an ohmeter.Check the ignitor wire for power,also,even though the dash light is on,just to be sure.
Good luck

good rebuilt alternators aren't very expencive, and usually come with a warranty. By the time you fix most alternators it cost just as much, and no warranty.....

Thanks guys, for the further input.

lowCG, I'm not too sure about cutting these particular wires because they are the main wires from the field windings, and there really isn't any slack to reattach things back together again. However, if I try it and I bugger it up, what have I got to lose, eh?

Ogre, you say rebuilt alternators aren't very expensive. Well, everything's relative I suppose. Compared to an engine overhaul, sure, an alternator's real cheap. But compared to spending $5 for a diode or whatever, a rebuilt alternator is pretty expensive at $118.

Your idea of removing the dogbone and shifting the motor sounds interesting. Kinda late for me now, but maybe someone else will benefit from your suggestion.

I could just barely get the alternator past the (long version) oil filter on the way out. I hate where and how that filter is positioned. Every time I replace it a lot of oil spills all over (and into) the engine cradle as soon as I loosen the old filter. What a stupid design!

But I digress. Anyone else care to comment on alternator repairs?

Too bad you live in Canada, winters suck and alternators are twice as expensive as in the States, but you do have great hockey and beautiful wilderness areas, so I guess it's a toss up. Maybe you ought to call a shop that rebuilds alternators and ask them how they get around your problem. Most of the times I've done that sort of thing they've been real helpful.

batboy, I appreciate your helpfulness, but the source you've found is located in Connecticut. I'm on the west coast of Canada. There's a few thousand miles and an international border separating me from that alternator!

Geez, the alternators on my old Chevies were so much easier to service...

you should be able to find a used one cheap.... they aren't anything special. Take the old one to the yard with you to get one with the back half turned the right way. (the back half can be rotated in diferant positions relative to the mounting ears to allow clearance for the wires.) You can rotate the case yourself but it's a bit of a pain.

I picked up a remanufactured alternator for my 84 4cyl for $40 at Discount Auto Parts.

I cant believe someone would charge $118

Ogre, I think I know what the pain is you're referring to. When I took apart my original alternator, one of the three bolts that holds the two halves together snapped off. This was after soaking everything in penetrating oil overnight. I know from previous experience that it is NO fun trying to drill a broken steel bolt (especially a small one) out of an aluminum casing. When I pick up a replacement alternator from the wreckers, I'll follow your advice about getting one that has the back half oriented the proper way. I wouldn't want to have to try and loosen the bolts on the replacement alternator and end up snapping one of those.

DJRice, yeah it's expensive living here. But you know what, it's worth it!

I thought all Fieros came with AC Delco model 12SI alternators or am I wrong on this? This alternator is simple and all internal parts can be easily replaced. Theres only a few: stator, brushes, diode trio, rectifier bridge, and voltage regulator.

I believe the alternator on the 4 cyl Patrick is refering to is a small case, Delta wound unit. For the most part, they are not rebuildable. I think they're called 10SI, not sure, but I'm sure they're delta wound. Remember the greek sybol delta? It's a triangle. That's the way the diodes are connected, end to end, in a triangle. All the parts are soldered together and really only come appart and go back together for the skilled rebuilder. You were correct in buying a re-man unit for fourty bucks. You can't get parts for them to recondition them over the counter. I saw a kit once in a JC Whitney's catalog to bump up the amperage and increase the longevity with a heatsink in a kit. It was pricey, but looked interesting.
Dan-O

The 10SI alternators are similar to the 12SIs, only with a metal fan instead of a plastic one. The internal parts are the same. The alternator you are talking about is one of those new types with small case and controlled by the ECM. These are expensive, my friend has a 89 Camaro and it cost him $180 to replace it. I don't think even the 88s came with these.

Hi guys. If the alternator wasn't so filthy, I could probably tell you some identification numbers. Forgive me for not volunteering to clean it up to read the numbers, but it hardly seems worth the effort to scour something I'm about to toss.

The only other things I can mention to help identify this beast is that it has a plastic fan which spins very close to a round plastic plate of the same diameter which, as I mentioned above, can't be removed (thus eliminating any and all access to the other components). The "crimp" connections that attach the three wires from the field windings to the regulator(?) are accessed from outside of the alternator AFTER a plastic plate is popped off the end of the unit.

This is unlike any other GM (AC Delco) alternator I've ever had apart. Of course, the "newest" vehicle I own other than the Fiero is my semi-retired ‘78 Z28 Camaro. I imagine alternators probably changed from ‘78 to ‘87, and unfortunately they appear to have changed for the worse. If items such as alternators can no longer be repaired by a backyard mechanic, then the manufacturers have taken a giant step in the wrong direction.

I did some research today at work. The small case alternator is a C-130 model. It has a plastic case access, like Patrick describes. It came in 85-105 amp models and is sometimes controlled by the ECM. It has the capability of being a stand alone unit as well, with no ECM/PCM control, as my buddy with a blown small block '72 Camaro has one that we installed for clearance. They charge very well at idle as well as at high RPM.
Dan-O

If Patricks alt. is one of those new fangled types, he should be able to replace it with a good old 12si. These are cheap, plentiful, and easy to fix.

Ok Paul, you've got my attention!

My concern is that the mounting would have to be the same, and the wiring harness would also have to be able to plug on properly.

I might as well hold off getting a replacement until Monday now. Especially if I can identify a different alternator to use with your fella's help which is "cheap, plentiful, and easy to fix".

Well Patrick, what does the wiring going to the alt. look like? The 12SI has only 3 wires going to it, The main red one is screwed into the back. This leads directly to the junction block near the battery and is always live, +12v. The other 2 plug into the back with a 2 wire into 1 plug. One of these is for the alt. light the other also supplies +12v.

The other question is, can your alt. bracket accept a 12si? I dont know the answer to that one.

Hi Paul. On the alternator itself, there is a stud where the main red wire is held on with a nut. The wiring harness plug in the car snaps into a socket on the alternator that has four pins in it. I don't recall how many wires there were on the harness. The fact that there are four pins does not necessarily mean there has to be four corresponding wires. I think there was only two (not counting the main red one), but I'll have to look at it tomorrow in the daylight. The wiring harness plug itself does NOT look like any other plug I've ever seen before on any of the ‘67, ‘70, or ‘78 Chevs that I've owned.

Regarding the alternator bracket, keep in mind that this engine has the single serpentine belt which is kept at the proper tension by a spring-loaded tensioner pulley. Every engine I've ever worked on before had a fan belt that was tightened by moving the alternator. If the alternator you're referring to was designed to work with the "older" style system, it's possible that it wouldn't mount properly on the "newer" style brackets that I have on this Fiero.

Well, however all this pans out, thanks for everyone's input.

Your right Patrick. You may not be able to use the older style alt. They (GM) probably were forced to use a smaller one when they switched to the serpantine belt. The pulley is not a problem, they have 12si's with them, its the mounting. When I was helping my friend with the Camaro, I made remarks about how small his alt. was. Then I thought they had to use that smaller one because it was mounted right in the center top front of his small block v8. The hood on that car is low.

Back to the basics boys. Patrick, if you live in western Canada (BC I take it) and you live somewhere close to the border of the US, scoot across to Blain or whatever border town is close, go to PEP Boys, AutoZone or any national car parts chain and pay $118 bucks and pick up the alternator. They all come with a life time warranty, (just keep the receipt). I've had to replace at least six of them over the years on my 86 GT and 90 Transport. Paid for the first one, the rest were exchanged at no charge.

Hey old man,

You've gone through SIX alternators on your vehicles??!!! Have you got them wired into the international power grid system or what?

Sounds like you're familiar with this part of the world. Blaine (with an "e") actually IS the closet American border town to me, but I don't know if it's really worth the hassle of crossing the border to get an alternator. When you start to add up the exchange rate, duty, GST (Canadian tax), gas expenses, and time, is it worth it?

These alternators you're getting from PEP Boys, AutoZone, etc, are no doubt rebuilt ones. The frequency with which you are replacing them indicates to me that the rebuild quality is dubious at best. A lifetime warranty is great except for the fact that I've really got no desire to be making a regular pilgrimage down to Blaine to be exchanging alternators on a regular basis.

No, I think I'll stick to buying one from a local wrecker and gamble that it'll last me for as long as I continue to own this car. But thanks for the suggestion.

It seems to me one could rip the system (avoid the tax) by driving into the US, changing the Alternator in the US and then driving back to Canada.....

Of course, This comes from a Florida boy who is about as far away from a foreign border as one can get. Of course, thats not counting having to hop a boat to Cuba or something.

I also dont know how tight the Canadian border is, but I heard you guys get wild sometimes so they might be watching things pretty tightly. HeHeHe

Well, after being couped up shivering in our igloos all year, it's such a release to cross that 49th parallel and immediately enter a world of sunshine and warmth and inexpensive auto parts. Sometimes we just go crazy and...

...I think I must have bumped my head changing the alternator on my Fiero...

Just a quick final note.

I had the old alternator put on a test bench just to make sure that it was faulty. It was. I asked for the price of a replacement alternator while I was at that particular shop. One Hundred and Thirty Dollars!!!(Cdn) I said thanks but no thanks.

I went to a local auto wrecker and got an alternator that must have been rebuilt just before whatever car it was in got cracked up. Really great condition. (The alternator, not the donor car.)Fifty bucks.

I'm a happy camper.