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Battery, alternator, or ?

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John_Mc

John_Mc

Jedi Knight
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Hi all. I'm sure there have been posts addressing this before, but my searching ability is almost as bad as my auto-electric knowledge. Yesterday, I drove my TR6 an hour and a half north. I started noticing that the ignition light required a little higher RPMs before going out. Then on the return trip I noticed that sometimes even at freeway speeds the light would start to glow dim, but increasing speed/rpms solved it. Today I went out and started the car no problem. Drove it 5 minutes to my office. then when I went to start it after it had sat for 1/2 hour the was almost no juice at all. Where do I start? Battery, alternator, or elsewhere? Thanks in advance for any advice. Everyone here has always been extremely helpful and I often fail to say thanks after I get answers.
 
I generally start with the battery. It is easy to pull it out and have it checked at most auto parts places.
 
Sounds like there is a closed circuit or short somewhere which is draining battery juice. Good advice above, start with the battery, then the alternator, then all the wiring.
 
Put the battery on the charger at home overnight, and then take the car to the nearest Autozone, CSK, etc. They can test the battery and alternator on the car and tell you whether there's problems with either. However, an easily overlooked thing is the battery terminals...are they clean? Doesn't take much to interfere with the electrics.
 
If the dash light started to glow, it's because the alternator output voltage was dropping below battery voltage. It's best to check the charging system as a whole, but you can check the alternator with a voltmeter. After you charge the battery, you can go through some voltage checks at various conditions. Start with a battery voltage of about 12.4+ volts.

First make sure that there aren't any mechanical issues such as a loose drive belt.

1. Engine at idle - no load - depending on how high the idle is, voltage should be above starting battery voltage probably 13.2+
2.Engine at higher rpm (2500-3000)- no load - voltage should increase to 13.8-14.2 or maybe slightly higher.
3.Engine at the higher rpm - with load - turn on every electrical appliance in the car - voltage will drop, but should not go lower then 13.0 volts.

If your voltages show up less then these numbers, the alternator is not putting out enough. To properly test the battery, you really need a load tester, but I would make sure that the alternator is good first. Your symptoms indicate that this is the problem.
 
Hello John,

the first thing to check in that situation is the fan belt. If that is tight then you need to go into the other things mentioned above.

Alec
 
As mentioned, start with the basics like checking the fan belt and the fluid level in the battery. If these are OK and putting the battery on a charger doesn't fix the problem it's time to look deeper.

As others have said, you can take the alternator and/or battery to places like Advance Auto and have the components checked. However, you seem to be describing something that they may miss. As mentioned, a glowing ignition light is an indication that the alternator output is too close to the battery voltage. Since your light is flickering and getting "better" at higher RPM, I'd make a quick check of the brushes after making sure the belt is tight. I've seen worn brushes cause the symptoms you're describing on "non-British" cars.
 
So, I've done as suggested. I freshened up the contacts of both + and - terminals and at the starter. Replaced (-) cable just to be sure. Checked H2o level of battery. Checked belt and tightened to be sure. Charged battery (which seemed to take a charge okay) and did voltage test as martx-5 suggested. Never got the voltage readings as described. Seemed to stick around 13.2-13.6 range even at 2500-3000rpm. Took it to Kragen Auto and they tested it in car and their results indicated alternator. SOOO...assuming it is the alternator at this point, how do I check brushes? Can brushes alone be replaced (they are only $3.40 at Moss)? And if not, should I have the Lucas rebuilt or go with Delco or other? Where would I go for rebuild (does it have to be a specialty british outfit or any alternator rebuilder)? Thanks again for your suggestions.
 
Brushes can be replaced, but I doubt that would cure the problem. It sounds like the rectifier has fried a diode or two...a weak point in that alternator. Most any decent electrical rebuilder should have the parts to rebuild your unit. If you don't mind not having originality, a Delco 7127 10SI unit is a good replacement. They are very robust, easy to get, and cheap compared to re-doing the Lucas unit.

Check through the procedure for replacement to see if it's something you want to tackle, as I think there are some mounting differences that have to be addressed.

Also, the often suggested wiring for the Delco unit works, but it is not the best way. They take the sense wire for the regulator and tap it right off of the main output stud of the alternator. It should be wired directly back to the battery, or some connector that the + battery cable hooks to.
 
If you want to get the current alternator rebuilt, look in the yellow pages for a shop that works on them and starters, commonly refered to as an "armature" shop or alternator repair. I've had my Lucas ACR25 rebuilt at one, and they even had the parts in stock. Depending on what's wrong, it will probably cost more than doing the Delco conversion, but you'll still have the original alternator.
 
John,
Rather than spend a bunch of money on overhauling your Lucas alternator, why not consider converting to a Delco-style alternator for less money and a lot more amps, which most people can sorely use. Brighter lights and more juice to help run extras like driving light, electric fan, etc. I made the conversion and was glad I did. (I will be running a 16" fan along with halogen fogs and headlights.) I went with the Autozone Duralast 3-wire @66 amps.

Bill
 
Brushes can be replaced but if you're measuring a steady voltage in the mid 13s, this wouldn't indicate brushes as I suggested earlier.

I have the Delco unit on my GT6 and it has proven to be a cost effective replacement to the generator. Once you invest in one from a national parts supplier, you'll have a lifetime warranted unit that can be replaced anywhere around the country. Obviously if originality is important to you... have the Lucas unit rebuilt or replaced as you see fit.
 
Follow up:
Thanks everyone for the input. It turned out to be the alternator as suspected, although the battery was very suspect as well. So I replaced them both and all is well. Local autoelectric place had a rebuilt Lucas in stock so I went with it, though I did consider the Delco. Apart from lack of screeching, how do you know if the belt is tight enough? Is it possible to go too tight, and if so, what might be the consequence of that? I ask because as soon as I replaced the alternator and fired the car up, it started overheating as it idled, which hadn't been a problem up to this point. I'm wondering if it's coincidental (cooling system is due for a flush)or related. Thanks again for all the help.
 
Yes it is possible to go too tight and ruin bearing in alternator. Should have enough play in belt to depress about 1/2 inch in center of long stretch in belt, which is purely a rule of thumb, but insures that it's not overtightened. If not sure, stop by shop that rebuilt it and have them check it.
 
The overheating may be a sign of the fan belt being too loose and not driving the water pump effectively.
The 1/2" deflection rule of thumb above is correct, I check mine by pressing on the belt section below the alternator.(engine off of course) /ubbthreads/images/graemlins/ooo.gif
 
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