Is it the alternator or battery?
 

I'm hoping you guys can give me a refresher on mechanics.

I have a '95 S-10, with a 4.3 V6. About 175,000 miles.

On the interstate coming home tonight, I noticed the voltage indicator on the dash was wavering between 11 and 14.

FWIW, the needle has been just below the 14 for a long time. I bought the truck used, and since it was wrecked sometime in its life, I figured that might just be the normal resting point of the needle at full charge, if that makes any sense.

Battery is about 2 years old.

I've not checked to see if the belt is still tight, or if the tensioner is okay. I just got home a few minutes ago.

Is there a way to check the alternator without removing it?

If I drive it to a parts shop that has a battery tester, will it tell me if the battery is still okay, or are those reliable?

Thanks in advance!!!!! I really appreciate the help!!!!

Clove

As long as the voltage is around 13.6 volts the system should be OK. Has the alternator ever had a set of the small brushes put in it?

You could put a voltmeter on the battery terminals and read the battery then start the engine and see if the voltage increases. If the battery has a good charge on it you may want to turn the lights on for a few minutes before starting the engine and then watch for the battery to recharge.

I don't know if the brushes have been replaced. They haven't since I've owned the truck, which has been 4 years or so.

FWIW, the alternator has a Delco Remy sticker and raised letters on the outside casting that reads "Delco Remy". Could it be that this alternator has lasted 15 years and 175,000 miles?

I did check the belt, it is aged, and needs replaced, but appears tight.

I don't know if I'll be able to pull off a test with a volt meter. Wife is already asleep, and will leave super early for work. Maybe I can catch the neighbor. Is there a way to check this by myself while still starting it???

Any other thoughts?

Thanks so much!!!!!

Start the truck and hold a screwdriver or knife blade in the area of the rear bearing boss on the alternator. If it is attracted/pulled up against the housing, the alternator is charging.

With the voltage fluctuating, I'd take a look at the wiring from the alternator to the battery, battery terminals and ground to the block.

Okay, I will.

A after a quick check of the wires, everything looks good, but I didn't spend much time with them.

I'm not sure where the ground to the block is. I'll have to figure that out.

When alternators go out, do they generally quit charging altogether, or will there be fluctuating voltage?

Thank you!!!!! (And I really mean it.)

BTW, it might be late in the day on the 17th before I get back to the thread. In the mean time, I've got to figure out a way to get to Indpls, just 30 miles away.

Please feel free to post. I can use the help and advice!!!!

Thanks!!!!!

My '89 S10 V6 has a ground wire connected to a bolt on the intake manifold near the alternator.

Might try turning on the headlights, wiggle battery/alternator connections while the motors running, and watch for dim/bright changes.

Unless the battery has be abused it's probably OK after 2 years.

The only alternator problem I've had was no output.

If the voltage is rapidly changing from 11 to 14 volts, you should see changes in the lights. Might be a gauge problem, do any other of the instruments read up/down with the voltmeter?

It's not your battery, it's the charging system. Which goes through all the connections.

Alternators wear their brushes, and when the brushes get worn to the point of barely making contact with the armature, weak charging and moments of no charging are the normal symptoms.

Use your multi-meter and put it across the battery. You should see about 12 volts with the engine off, and about 14 with the engine running. If you don't see this increased voltage, you don't have charging taking place. It can be from dirty or loose connections, but since you describe voltage drift, worn brushes are the most likely culprit.

Alternators do fail completely, but that is usually because a diode goes out in the rectifier. You aren't describing that symptom (no charging, with sometimes a little charge at high engine rpms).

Clovis,

The alt in my '88 S-10 lasted 218,000 miles, the one in my '93 Jimmy lasted 100,000. The one in my '99 Grand Am lasted 54,000 & the re-man replacement has lasted 130,000 so far...

You never know when they will go bad or how. The one in my Jimmy toasted a bearing and siezed up stalling the 4.3, never thought a serpentine belt was that effective...

Since GM uses 'side post' batteries, make sure the connection bolts are clean and tight. check the outboard ends of the ground(s) and use a mirror to check the ground straps from the rear of the heads to the firewall...corroded grounds make electrical systems do funny things. If this condition persists after cleaning the grounds & is verrified by a voltage meter, you need a new alternator.

On my 84 S10, if the alternator belt wasn't tight it didn't charge correctly.
If I were you that would be the first thing I checked.. It has to be tight, same goes for our 96 Olds also.

Thank you for the replies!

I talked to a local auto electric shop today. They said that I have a CF100 alternator, and "if the volts are fluxuating like that, you need more than brushes. That might be true on some alternators, but not the CF100's."

I still haven't checked the system with a volt meter.

All wires, including the battery terminals, are clean and tight.

The serpentine belt is tight too. This is one of the first things I checked, thinking the belt tensioner was bad.

You know, at least around here, when it rains, it pours. I've got more irons in the fire than I can handle, and now have a problem with the old truck.

I'll check it with a volt meter in the morning. My buddy should be here to help with the firing of the truck.

Possibly, but there's a reason brush kits for that alternator are sold at virtually all auto parts stores cheaply. It's because it's the most common thing to fail. When it does, the voltage goes wonky, low, as it intermittently fails to charge.

And it should be a CS130. There is no CF100 alternator that I recognize.

Auto Zone and Advance Auto both check alternators and batteries for free. Some even check voltage regulators. The parts don't have to be off the car. Call to make sure they have the equipment and a tech available to do the tests.

[QUOTE=foxtrapper;4336089]Possibly, but there's a reason brush kits for that alternator are sold at virtually all auto parts stores cheaply. It's because it's the most common thing to fail. When it does, the voltage goes wonky, low, as it intermittently fails to charge.

[QUOTE]

Are the brushes hard to change? Does the outer aluminum case have to come off?

This is good to know. Thanks!

Clovis

I read how the CS-130 alternator functions and I think with the way it regulates that what you are seeing is not abnormal. Additionally what I read mostly discusses a light being used to determine the condition of the charging system instead of a gauge. I believe if you were to have the alternator tested it would read OK at an auto discount store.

So, are you saying that the alternator is okay, and working fine, and the fluxuations are normal?

I, too, am worried that the alt will test okay at a store. I had that happen once, but cannot, for the life of me, remember what I was working on at the time. In that case, the alt happened to check okay more than once when tested at a retail store, but was not charging when in the car.

Ok I didn't see a post where you said if the battery went dead or you are just getting a funny reading on the gauge. When checking take a reading with everything off and then with everything on. If it falls below the 13.6 volts you need to replace the alt. Good luck. Sam

Sam-
The battery has not been dead at all. I am just getting funny readings on the gauge on the dash.

I'll check it out with a volt meter tomorrow. (I've been super busy the past two days.)

Clovis
The CS 130 uses a different method to regulate the charge. It turns the charging on and off at intervals, rapid intervals depending on need of the battery to be charged. IMO, the voltmeter movement is nothing more than the voltmeter sensing those cycles.

Nope and nope. Remove the back cover and then remove the brush holder.

Beware of their testers.They told me my alt was good on 2001 Jetta,and thing had a bad voltage regulator.Then tested 3 of theres at their place and all three tested bad.

I now dont trust them at all for alternators.

If you happen to have a good but dead battery around you could put in the truck, jump start it, let it run awhile, and see if it charges the battery up.

It is the same a some camaro alts w/ the case 'clocked' a little different. When mine was bad the local parts guy had the camaro one and re-clocked it so I could use it instead of waiting for his re-stock. He was the last 'old time' parts place 'round here, there is only one 'non chain' parts store around and they do alot better than advanced auto crap or pep boys...they can test a starter or alt too but you have to carry it in.

mightybooboo, good to know. I can't help but wonder if the tech knew how to read it.

We had a car with a bad voltage regulator, before Parts America had the equipment to check regulators. Every 6 months we had to replace the alternator which did test bad. After the 3rd alt the tech on duty suggested the regulator. 2 years later when the car finally died the alt was still good.

Reasonable idea to try.
An alternator is a voltage maintainer, not a charger.
Most alternators go bad because they have an amp sucker on board, be it a weak battery or a sound system that they have outlawed the volume in most cities.

I had the same problem on an 87 GMC pickup. I thought it was the alternator but didn't change it to see if it crapped out altogether. It never did and I had it for 225k. The guage started acting up about 75k.

So, is it worth trying new brushes?

Would I be throwing good money after bad?

If I do change the brushes, I remove the alternator, and then remove the black cover on the rear of the alternator housing?

I'll find the brushes in there? Any special tricks that I need to know about this job?

Foxtrapper...are you in the rebuilder business? You seem very knowledgeable about these alternators.

Thanks!!!!!!!!!

You will see 2 small holes in the back of the alternator. Use a paper clip in the holes to hold the brushes in when you stuff it back together. Mark the position it was in before you take it apart so it will be 'clocked' the same as it was before.
The backside half comes off. Leave the metal ring looking thing that is between the halves there with the front half. Use a bladed screwdriver and pry it apart.

The brushes are the 2 square graphite looking things that have springs behind them.
That's why you need the paper clips to hold them in. They will fly out of there when you take it apart but they are attached so they won't fly across the room.
Take your time and take mental notes. It's not hard to do.

If that doesn't help, I tried.

Fixer,

You make this sound like a possible alternative. It doesn't sound like rocket science.

I think I am going to try this.

I do very much appreciate your help!!!!!

Things that are not broken I leave alone. I have enough problems fixing those things that do not work.

No guarantee clovis that replacing the brushes will fix the problem. I will say that your symptoms sound like worn brushes to me, and you can buy new brushes for about $5-10 dollars. Invariably, web stories always leave important details out. But, based on what I've got to go on in this thread, worn brushes are quite likely in my opinion.

Brushes can often times be replaced with the alternator on the vehicle. Not as much fun then, but technically its possible. I far prefer doing it off the vehicle and on the work bench. There really aren't any special tools needed, and it's not a complex job. This link gives a pretty good overview of the alternator, complete with lots of pictures. Follow through the pages.

http://www.alternatorparts.com/cs130_sbpage1.htm

There is something to be said for the notion of ignoring the symptoms until they become a real problem. I don't particularly go with the notion, as a wonky alternator tends to become a dead alternator only when you're way on the far side of some distant mountain. But....

And no, I'm not in the alternator rebuilding business. I'd remember the details of the CS130 better if I were. I just work on a lot of machinery.

Here is some follow up:

For a number of reasons, but also in a moment of weakness, I brought a new alternator instead of swapping the brushes. I called a buddy of mine who is an experienced mechanic, and he was pretty hesitant that brushes might fix the problem. He called another friend who is in the rebuilding biz, and he was hesitant that brushes were the problem too.

The alternator definately had a bearing going out. It might have lasted 50K more miles, but it was definately making a noise while it spun.

I also needed the truck today.

I hated to give in and spend the money for a rebuilt alt, but it was easy and fast. I just hate the fact that I couldn't learn more about alternators and rebuilding.

THANK YOU SO MUCH FOR ALL OF YOUR HELP!!!!! I HONESTLY APPRECIATE IT!!!!!!

clovis,

Did the voltmeter settle down?

Yes, so far. There has been very minor fluxuations, as to be expected, but not the quick, and sporadic movements between 11 and 14 volts like there was.

Again, thank you for your time, help and expertise.

If you read the fine print on the warranties on rebuilt alternator, if alternator has external regulator, then you are REQUIRED to replace the regulator with new one at same time you install the rebuilt alternator or warranty is void. They tend not to rigorously enforce this, but ...

I think you are better off just changing the alternator instead of piecing it together.

If you still question the alternator, you could just hook a volt meter to a power source and check it against you guage when you are driving around to see how accurate it is.

I didn't know that.

FWIW, I buy 99.99% of my auto parts from a locally owned Carquest dealer. They have been awesome to work with. This alt has a lifetime guarantee. I've never, ever had a problem with any returns there, but then again, I've been buying from them for 25 years.

They have an excellent reputation around town, even though we have 3 other corporate giants in town, not including NAPA.

This is also good to know.

You know what I love about this forum? You learn cool stuff like this!!!!

Again, thank you so much for your time and help!!!!!

GM uses an internal regulator [diodes]...