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Old 06-04-2019, 12:24 PM   #1
Ad Cam
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Battery dies after driving

Hello! My '76 is acting up. It starts no problem when I take it out. If I drive it to work (half an hour commute) it's fine. But if I shut it off and try to start it again immediately the battery is pretty much dead. I can let it sit for 15 minutes and suddenly the battery has enough life to start it. Battery is brand new, and it replaced another new battery that I thought might be bad. I had the alternator tested (it's a remanufactured 12si) and they said it checks out fine. Engine is a 350. Any thoughts on what could be dragging it down? Should I get a new alternator? Thanks for any help.
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Old 06-04-2019, 01:38 PM   #2
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Re: Battery dies after driving

My truck was recently behaving the way you describe. I started this thread http://67-72chevytrucks.com/vboard/s...d.php?t=787371 and got a number of suggestions that may help you as well. In my case, it looks like most of my problem was that I wasn't getting good enough ground on my engine block.
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Old 06-04-2019, 02:21 PM   #3
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Re: Battery dies after driving

Firstly, verify the battery is actually the problem. I would consider the battery dead if it drops to less than 10v while cranking. Batteries don't recharge themselves from nowhere. This sounds like a starter issue to me.

I would -
Make sure the connections at the battery are clean and tight.
Make sure your grounds are installed to a clean place on the block and tight.
On my truck, I ran a ground directly to the stud on the back of the starter.
Make sure the positive wire is clean and tight on the starter.
Check that your starter signal wire is getting 12V.
If all else fails, replace the starter. Many have said the gear driven starter from a 98 Tahoe is a good upgrade. Takes less power and turns the engine over faster.
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Old 06-04-2019, 03:30 PM   #4
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Re: Battery dies after driving

The problem could be a heat soaked starter. After they cool they will turn the engine over as usual.

I had this problem on a '76 350 back in the day and replaced the starter to solve the problem. I use the smaller gear reduction starter on my current truck and it does well.
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Old 06-04-2019, 04:03 PM   #5
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Re: Battery dies after driving

+1 weak starter. Had the same symptoms last year and ended up stalled at a light having some strangers help 'pop' start me in traffic so I could make it to the parts store and get a starter. Been great ever since.
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Old 06-04-2019, 04:17 PM   #6
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Re: Battery dies after driving

No gauge to see if it's charging?
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Old 06-04-2019, 04:50 PM   #7
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Re: Battery dies after driving

Had a similar issue. Turned out the starter brushes were worn out. A $4 set of brushes fixed the problem.
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Old 06-04-2019, 05:57 PM   #8
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Re: Battery dies after driving

Quote:
Originally Posted by rgunlock View Post
My truck was recently behaving the way you describe. I started this thread http://67-72chevytrucks.com/vboard/s...d.php?t=787371 and got a number of suggestions that may help you as well. In my case, it looks like most of my problem was that I wasn't getting good enough ground on my engine block.
To clarify, I believe that my starter has also gotten weak. There are still times where you can tell it struggles to get the engine cranking, but since re-doing my ground to the block at least it does crank. I will likely be replacing my starter soon. Also, BTW I have stock manifolds, not headers on a crate 350 but I still believe that I am getting some heat soak on the starter (or solenoid).
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Old 06-04-2019, 06:45 PM   #9
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Re: Battery dies after driving

I was just about to post something similar - I've been rewiring my 76 and finally got it all working and the battery just drains instantly. I removed everything to check for a parasitic drain and found nothing. Jumped the truck and got it running, 5 minutes later try to start again and the battery is drained to 9v. I thought it might be the alternator but I probably should check the starter.
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Old 06-05-2019, 06:35 AM   #10
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Re: Battery dies after driving

Funstuie:
Simple check for the alternator is check the voltage while running, should be around 13.5-14.5V
Did you use an ammeter for the parasitic load test?
Do you have a battery charger? Charge it up. Try to start. If it drops below 10V, replace the battery.
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Old 06-05-2019, 10:07 AM   #11
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Re: Battery dies after driving

I had the same problem,thought it was heat soak but found my dist had slowly walked and made the timing off which made it hard to start when hot
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Old 06-05-2019, 11:29 AM   #12
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Re: Battery dies after driving

Quote:
Originally Posted by rpmerf View Post
Funstuie:
Simple check for the alternator is check the voltage while running, should be around 13.5-14.5V
Did you use an ammeter for the parasitic load test?
Do you have a battery charger? Charge it up. Try to start. If it drops below 10V, replace the battery.
When I jumped it the bolts were hovering around 13v but it still was hard to start. Got it started left it running for a few minutes, turned it off and working 5 minutes battery had dropped to 9v. The battery is brand new.

So Iím not sure what it is but the started sounds like crap. Itís clattering and really struggles to get going.
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Old 06-05-2019, 01:32 PM   #13
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Re: Battery dies after driving

13V before you started it or while it was running? A few minutes isn't really enough for an alternator to charge a battery.
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Old 06-05-2019, 01:35 PM   #14
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Re: Battery dies after driving

Also keep in mind depending on your style alternator some need to see ~1800rpm to excite and charge. If you start and idle it isn't charging until you rev it up.
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Old 06-05-2019, 04:52 PM   #15
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Re: Battery dies after driving

Quote:
Originally Posted by rpmerf View Post
13V before you started it or while it was running? A few minutes isn't really enough for an alternator to charge a battery.
13v while it was running.

So today I went out and purchased a new booster/jump pack. Hooked that up (as my wife is out I couldn't use her car to jump my truck) and after a while started the truck. The amp meter showed 13v while running. I revved it a few times (I can't drive it at the moment as it's got no interior) and left it running for around 30 minutes. I went inside to do some errands came out and tried to start it up and it's completely dead. Hooked up the amp meter and its showing as 8v - this is around 20 minutes later.

I don't know what could be causing the battery to drain that quickly.
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Old 06-05-2019, 08:20 PM   #16
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Re: Battery dies after driving

Get a voltmeter, measure across the battery with the engine off, running and cranking. Might try checking the battery voltage after turning the engine off, then at 5 minute intervals for a while to see if it's going down. You might have something drawing current w/ the key off...
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Old 06-05-2019, 09:08 PM   #17
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Re: Battery dies after driving

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Originally Posted by franken View Post
Get a voltmeter, measure across the battery with the engine off, running and cranking. Might try checking the battery voltage after turning the engine off, then at 5 minute intervals for a while to see if it's going down. You might have something drawing current w/ the key off...
I put an amp meter on the negative side and thereís a 2.6amp draw!! I pulled all the fuses and it was the hazards fuse when I pulled that the amps draw dropped. I think I have a short somewhere.

I also think the battery is screwed. Itís disconnected now and recharging and itís not taking the charge.
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Old 06-06-2019, 06:06 AM   #18
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Re: Battery dies after driving

That will do it! Should be less than half an amp, and in a vehicle that old, I would expect closer to 0 when the truck is off. I might be looking at another alternator also. 13.0 seems low. I would prefer to see closer to 13.5-14.5v while running.

Some chargers won't charge it if the voltage is too low. Hook it up to the jumper to get the voltage up, then hook it up to the charger.
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Old 06-06-2019, 10:41 PM   #19
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Re: Battery dies after driving

Just an FYI, but I'd pull only one side of a glass fuse so the fuses (of different ratings) don't get confused.
I'd also let the battery charge for a few days on a slow charge.
People like to make suggestions and say swap parts, but troubleshooting will save time and money...
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