Hagerty.com

When a chronic dead battery just means a broken alternator, the fix is simple

One of the venerable vehicles I’m always messing around with is my 1977 Chevy C20 Suburban. It’s a little weathered around the edges, but I love it. These “Square Bodies” have a wonderful following, and most everything is really simple to work on.


This is a companion discussion topic for the original entry at https://www.hagerty.com/articles-videos/articles/2019/02/25/replacing-a-broken-alternator

Diagnosing and replacing a bad alternator is cool, but why didn’t you take it to the next level and rebuild it yourself? I understand that it was an inexpensive unit, but for about $15 you could have done a rebuild on it and shared that information with the class as well. Most parts stores still stock the rebuild kits and a GM alternator is dead simple to rebuild. Maybe when the starter goes you can do a rebuild on that for us.

Bite your tongue! That is a marvelous beast!

Here’s another piece of advice: If you think you might have a bad alternator, you can remove it and have it bench tested on an alternator-starter test machine. Many auto parts stores have these kind of bench testers and will check your alternator for free. Such a test will show if your alternator is producing the correct charging voltage and current (amp output). If your alternator tests bad for either one, you need a new or remanufactured replacement. But if your alternator tests good, your charging problem is not your alternator but something else such as a bad external voltage regulator (if your car has one), a loose, corroded or broken wiring harness that connects to the alternator, or even a loose, broken or missing ground strap between the engine and chassis.

My wife’s Camry had the same problem, I found that the voltage regulator had gone bad and replaced it with little difficulty other than a bit of time. I also checked the brushes and found they were barely worn. Since getting that done, there have been no problems electrically.
Just took a little time and patience.

I also have a 1978 Chevy Suburban C20 2 wheel drive 454 CI , turbo 400 trans. With tow package . It’s a one owner Az. Vehicle I found over a year ago . Very silmalier paint . My valve covers are factory blue thou . It just turned 100 K miles & runs like a top . I’m detailing it out & is factory original . It’s turns head & we Love it . Heart beat of USA !:liberia:

A lot of charging problems can stem from bad battery connections, I like to take them apart about every two years or so, be they GM side post or the upright, clean them well then apply some wheel bearing grease, bolt them up again. If the bolt in the upright post type are looking corroded I put new ones in, a little grease here goes a long way to prolong problems but tends to make fingers a mess. When all connections are good, and this includes your ground connection on engine or whatever, salt spray in winter can cause rusting, I clean and grease these also.
Happy motoring … Warren in MN

So what’s going to break next?

If it’s anything like my 1971 Plymouth slant six and its more-powerful replacement alternator, two fuses, one at a time on separate occasions when you have no spares and are thus stranded; and then the headlights :stuck_out_tongue: I’m now having troubles idling which maaaaaay be connected to electrical, and perhaps the alternator straining these old parts.

Make sure you test the cables also - in my TR6 I was seeing only 10 volts at the battery but a little over 14 at the output of the alternator with the engine running. The voltage drop in the main cable from the alternator was running nearly 5 volts, normal should be under 0.5 volts even at high loads. In my case, it was a dirty, corroding tab at the connection point. I cleaned both sides with emery cloth and a small wire brush, applied some dielectric grease and the voltage drop reduced to 0.2 volts with 13.8 at the battery. You can even have issues on the ground side too. Bottom line - break out the multi-meter and test, test, test !!

1 Like

Hi , i read the article and i have the same problem with my 88 corvette. I park it with fully charged battery showing on my meter 4 days later its dead, but if i remove the cables from the battery that doesent happen.Do you have any ideas on how to track the voltage loss. One other thing, after the wires get hot and smoke you need to watch them because the heat makes the insulation on the wire get brittle and down the road with engine vibration bits start falling off. I know because i have been there.it makes more smoke.!!!

You may be having the same problem I have (or had) with my 2000 VW Golf. The car ran great and the battery normally stayed charged, but if I left it a week or so without driving it, the battery would be dead. I suspected the alternator, but it was fine, with the voltage going to 13-14 volts with the engine running.

So I decided there might be a drain on the battery when the engine was off. To test this, I bought a battery-disconnect gadget at the auto parts store. That solved the problem completely, and the electrical system worked so much better than before that I decided to leave it installed permanently. Now I just disconnect the battery whenever I put the car away for the night. I seldom drive this car more than once or twice a week, so it’s not a problem.

Simple test is to pull car in garage at night shut car off and shut door. Loosen a battery cable turn off the light and pull the cable off the battery, if you see a large spark there is something pulling voltage from the battery. Next pull fuses one at a time and pull and replace the cable each time replace fuses that do not make a difference till the battery cable does not spark any longer. Look at the fuse tray to see what the fuse runs. This is what maybe drawing voltage from the battery and draining it till it is dead.

Looks like the free Harbor Freight volt meter worked perfectly!

Thanks, i only drive the corvette 2 or 3 times a week at most in summer, so i have been popping the hood and taking off one cable till next time. I didnt know about a disconnect being avaliable. I was thinking of putting in a house circuit breaker in line under the dash , I will get what you suggested for summer ,thanks again.
B

john burrows

Guys,This how to test an alternator .1) Get the car started with charger, remove the charger when running . 2 )While the car is running pull off the negative or black battery cable, if the car still runs. It is not the alternator. 3) If the car stops . it is the alt. or regulator. 4) To test the regulator ,take a piece of wire strip the ends , connect one end to the + side of the battery , and the other end to the ( F) That means field side of the regulator .5) start the car, pull off the (-) side of the battery. if it still runs, it is the regulator . if it stops it is the alternator .No voltmeters needed .I explained the best i can,This entire thing takes 5 minutes .Mechanics from the old days know stuff ,and we want to share our stuff with guys who care about old cars.

The disconnect actually didn’t solve the problem! It avoids it. The drain is still there and may still cause a problem down the road (literally!) It could be a minor short that can get worse over time. I think tomcatah2’s approach to trying to diagnose the drain is a good one. I have to do the very same procedure on my car!

1 Like

@michaelankerberg - The process of removing the negative battery cable after the car is running does work on older cars, however it is inadvisable for modern cars. Modern computers are sensitive to an action like removing the negative cable and doing such could fry a computer or cause other electrical damage.

Best practice for modern cars is to get the car started, then put a load on the alternator by turning the blower motor on high, turn on the high beams, radio, any other easy electrical items and THEN testing the voltage at at the alternator. this will tell you if the alternator is able to keep up with the load safely and without damage.

“So what’s going to break next?”

If it’s like all other GM’s of its era, the starter will be next, then the carb, then the turn signal switch, then the inside door handle, then the…

A simple fix for a simpler car, but can someone tell me what the heck is going on with my 2010 Honda Odyssey’s alternator. It stopped working 6 months ago and even though I had not bought the alternator that came on the “truck”, the major chain from which it was purchased replaced it under the lifetime warranty because they still carried the exact same part number alternator. Then last week it stopped charging again and again the same auto store replaced it under warranty. Now it is good that they honored the warranty twice, but it is no easy task to get that alternator up from the bowls of the engine bay on an Odyssey and I don’t relish having to do it again in another 6 months. Folks on the Oddy forum say unless I buy a new Denso (obviously not a warranty replacement but a new $250 investment with only a one year warranty) that I will be replacing the Mexican remanufactured unit again in the near future. Why are these remanufactured units so unreliable? And why would a Denso with a one year warranty be so much better?

1 Like

I have a 2001 Pt Cruiser I ordered and bought new. It is my daily driver and at this time I am less than 15K miles short of 500 K miles on the odometer and the car is better than 98% original (only maintence items and minor replacement pieces). Just to be safe I take tools and coveralls with me on long trips. The biggest concern is the original alternator. It will not be a road side fix because you have to drop the right lower front suspension to replace the alternator. I don’t want to carry that amount of tools in my trunk. My wife wants me to change it before it fails but if I do that I’ll never know how far the alternator would have gone. When it does fail I hope it is nice weather and close to home. With my luck it will be Kapuskasing Ontario Canada in January at 3:00 AM. This Pt has been a great car!