Moss Motors, Ltd

Hello, all.

This morning, I started the car as usual and all seemed fine. She backfired once thru the carb, and ran with what seemed to be reduced power, but we got to my destination okay. As I was pulling onto a main drag, the wipers went slower and slower and the radio quite playing and the dash lights got dimmer and dimmer, and she died. The battery was dead. I called for reenforcements and when my daughter arrived, we took the battery to Advance Auto to be checked out. It was low and after charging for about 90 minutes, checked okay. I put the battery in and she started right up. Drove back to Advance Auto and had them check the charging system. He said that there was no charge going to the battery; I was running on battery power.

The alternator light comes on and goes off; it has since I bought the car. The last time that I took the alternator in to have it checked on the bench, the place said they didn't have the equipment to check it. Any thoughts on how to check the system and determine what the problem is?

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Happiness is an MGB!

zach,

Surely there is an auto electrical specialist near you somewhere. Take the alternator to them and have them check it. I'm not sure why the auto parts store couldn't do it. Plenty of folks around here have gone that route. I don't want to suggest laziness or CYA attitudes in my skeptical way, but...

Generally, if you use a volt meter and check the resting voltage at your battery, leave the volt meter hooked to it, start the car, and note the voltage rise as the battery recovers from starting, you'll get a good idea of the health of the alternator. Just above idle, you'd like to see it settle at between 13.8 and 14.4 volts. Note whether it rises at all above the initial resting voltage as well as how fast it recovers from the "strain" of starting. If it doesn't respond withing fifteen or twenty seconds, you've more than likely got a bad alternator. Some auto electrical specialists can repair them for less than the price of a rebuilt. Let me know what you're finding.

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Motorbill
From Lola to Land Rover, If it's British and has wheels, it's likely I've bloodied me knuckles thereupon

Bill,

I've been working OT at the office and didn't get an opportunity to check it out until today. With the voltmeter in place as you described, resting voltage is 12.2. On start, it climbed pretty quickly to about 13.9, but once the cooling fans kicked in, the voltage dropped to 11.5. With the fans off, it settled in at about 12.1.

Sounds bad, right?

zach

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Happiness is an MGB!

zach,

It's odd that it initially got as high as 13.9, but wouldn't resume there after the fan load was removed. I wonder if you've got a bad solder connection at one of ther diode leads in the alternator. Just speculation. It could be that it's making and breaking depending on load and vibration. Have you found a service place yet?

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Motorbill
From Lola to Land Rover, If it's British and has wheels, it's likely I've bloodied me knuckles thereupon

Hey, Bill.

I've checked the phone book for a place and the only promising one wasn't open when I called. I'll try again on Monday. The three main chain auto parts stores in Tulsa are unable to check it either because they don't have a chart, or they don't have the correct connector. Pep Boys said they could check it, but once I got over there with alternator in hand, they didn't have the right hardware to mount the alternator in their tester!

I've been mulling over whether to do the Lucas to Delco swap, because I've heard that the Delco is more durable, more powerful, and less costly. However, I went by one parts store today looking for the necessary parts to do a swap and in passing, asked the clerk what an alternator for a 77 MGB would cost. He brought up a Beck and Arnley (?) rebuilt alternator with a lifetime warranty for $59.99! At that price, I don't believe it would be worth it to do a Delco swap. What's your opinion?

zach

I miss my MGB!

 

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Happiness is an MGB!

Zaaaaack,

 A lifetime warranty for 60 bucks! Even if the alternator isn't the problem, such a deal!

Go for it, then go for a drive, driving season is getting shorter every day!

BTW, if you have access to an oscilloscope, you can take a look at the DC. That would tell you if you have a diode problem as motorbill suggests.

 

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On their death bed, nobody ever said, "Gee I wish I'd spent more time at work!"

hey guys.... just curious if engine compartment "temperature" could be affecting the diode too ?  I'm thinking, heat=breakdown..... or perhaps heat=exacerbating solder connection on the diode?  guess this thought is moot since it's got me thinking right back to Bill & Davey's path that it's the diode.

 Ed - Davey's right!  I'm contemplating the Delco conversion too - and for $60, I'd drive right past a table FULL of Lucas dynamos..... 

 Yeah man!  get 'er done and get back on the road before the season's over.... 

 p.s.... my tach is workin' so sweet now!!  calibrated it and the idle and carbs are set -- she's a purrin' spot on at 1000 rpm at idle...  whoohoo!

let me know if you do the delco-dance......  I'll take any hints from ya'.....

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Lou
'76 MGB MKIII

Yeah,

Stick the sixty buck rebie on there and see what happens. At worst you'll never have to buy another alternator for this car!

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Motorbill
From Lola to Land Rover, If it's British and has wheels, it's likely I've bloodied me knuckles thereupon

Sorry to take so long in getting back to ya', but OT and Ike have been in the way. (We've gotten a lot of rain and Texans from the hurricane.) I purchased the rebuilt alternator for a grand total of $65.00 with a lifetime warranty. I installed it today and she is holding steady at about 13.8 volts, but does drop when the fans and lights are all on. However, it does recover to 13.8 and the battery is charging well. It is so good to get back in my MG!

zach

 

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Happiness is an MGB!

Zack...Don't worry about the full load drop, that's normal.

It sounds like you're back in action just in time for the clearing skies!

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On their death bed, nobody ever said, "Gee I wish I'd spent more time at work!"