Dead batteries

[rfischba1]

I picked up a blazer from GL this week, batteries were dead, got a jump from a duce and let the truck idle 45 min. drove the about 5 miles home. When I tried to start it batteries still dead.
Should the batteries charged after running the engine for over one hour, or if they are really shot they will not hold a charge?
I do not have a tester.

 

[emmado22]

They will only charge if the alternators are good.

 

[maddawg308]

Take the batteries out of the truck, put them on a charger and see if they improve. If so, great. If not, then new batteries are in order.

It's a standard 12 volt alternator, you might want to take it out and take it down to Advanced Auto Farts or a similar place, they can test the alternator for free. If it's not good, they can get you a rebuilt one for less than $100.

 

[emmado22]

It's not standard, it has an isolated ground...

 

[rfischba1]

Which alternator charges the batteries, left or right, or both, also which is the cranking battery, back or front?

 

[maddawg308]

It's not standard, it has an isolated ground...

Would that make a difference in its replacement? I've heard of a couple folks replacing CUCV alternators with commercial off-the-shelf rebuilt units, and I never heard anything bad happening afterwards...

 

[Sephirothq]

If the batteries are too far gone they will not take a charge. Then they are junk. They would need to be replaced.

 

[tmbrwolf]

If the vehicle ran I would think the alternators, at least the driver side is working, if it wasn't the truck would have died as soon as you pulled the slave cable. Were you able to just hook up the duece and start it? The reason I ask if that was the case the front battery had to have some charge, it provides the 12V to the truck, where both batteries provide 24V for starting. The driver side alternator provides 12V to the truck and front battery, it also feeds the passenger side alternator at the ground stud for that alternator to produce 24V for BOTH batteries. On the driver side alternator it wouldn't make a differance if it was isolated ground or not, on the passenger side it will, the driver's side feeds the passenger side with +12V into the alternator at the ground connection to get the 24V output from the pass side alternator (driver's side is grounded to the block), if the pass side wasn't isolated it would create a dead short to ground! If the alternator is bad it's usually the regulator, most parts places have the regulator and brush sets on hand and they are really easy to install, have to remove the back of the alternator install the new parts, use a paperclip to hold the brushes in to reassemble.

 

[CUCVFAN]

The standard CUCV system uses a pair of 12V alternators, but the isolated ground allows the passenger alternator to only worry about it's own 12V battery. But, it does NOT charge both batteries. It's ground is referenced to the negative post (which just happens to be the positive post of the front), but it's only charging it's 12V system. If it charged both batteries, you would have an imbalance occuring, just like the M1010...

Needless to say, if the alternator lights were not on, the batteries are probably toast.

 

[rfischba1]

I think its the batteries, I have one on charge right now, should I use the slow charge ver night?
And yes when jumped with the slave cable, started right up and ran after it was disconnected. Drove 5 miles home and after sitting a few hours was dead again.
Any suggestions on Costco or walmart batteries?

 

[tmbrwolf]

CUCVFAN, not to argue with you but please look at the wiring diagram, the left (drivers) alternator, provides 12V to the terminal board on the firewall next to the glow plug relay, then continues to the right (passenger) alternator's "ground" stud, hence the need for an isolated ground (at least on that side), by doing this the output of the right alternator was doubled to 24V, the right alternator's output is then connected to the 24V terminal board on the firewall, providing power to both batteries, the wiring diagram indicates this by labeling the left alternator as "front battery charging" and the right as "both batteries charging" this will not cause an imbalance as the left alternator only provides current to run the 12V side of the system. In the army when these trucks were issued we had to go through a class to learn to repair these systems being "quasi" 24V. Now the M1010 goat rope electrical system, well if I could find the guy that designed that, I'd give him 20 lashes with a wet noodle

 

[rfischba1]

batteries

I charged the front battery, which was dead, checked the back battery, fully charged, cleaned up the posts and the truck started right up and restarted.
I'll have to see if the front battery will hold the charge, if not I've got a bad one.
Alt lights go out after motor starts.

 

[CCATLETT1984]

It's not standard, it has an isolated ground...

Would that make a difference in its replacement? I've heard of a couple folks replacing CUCV alternators with commercial off-the-shelf rebuilt units, and I never heard anything bad happening afterwards...

MD, do i need to get the newspaper?

DO NOT REPLACE WITH A STANDARD ALTERNATOR. IT MUST BE ISOLATED GROUND.

 

[CCATLETT1984]

Which alternator charges the batteries, left or right, or both, also which is the cranking battery, back or front?

Drivers alt charges front battery, passenger alt charges rear battery.
Both batteries are used in cranking.

 

[emmado22]

To REPLACE it, it needs to be one with an ISOLATED GROUND...

To repair/rehab it, make sure the automotive electrical shop knows it has an isolated ground, and they NEED to keep it that way...


Dont follow Maddawg's advice, bad things will occur with your CUCV electrical system.

 

[CCATLETT1984]

To REPLACE it, it needs to be one with an ISOLATED GROUND...

To repair/rehab it, make sure the automotive electrical shop knows it has an isolated ground, and they NEED to keep it that way...


Dont follow Maddawg's advice, bad things will occur with your CUCV electrical system.

Fireworks and welding under your hood aren't good things

 

[CUCVFAN]

the wiring diagram indicates this by labeling the left alternator as "front battery charging" and the right as "both batteries charging"

I understand what the TM says. It is wrong. True for the M1010 (and some M1028's), not the others. The system just doesn't work that way. I actually thought the exact same thing until Ida34 pointed out that it was not the case, so I take no offense at your raising the issue. Re-examine the diagram, and you will find this to be true, too.

Yes, the output of the second alternator is "24V" if you compare it to the vehicle ground. However, since it's ground is hooked to the rear battery negative, it is only charging that 12V system. It does nothing to charge both batteries. It CANNOT. It's charging circuit does not include the front battery at all. The isolated ground keeps it, well, isolated from the other, separate, 12V system of the front battery. If it's not a 24V alternator, it cannot charge a 24V system.

If it was 24V, you would not need to isolate it's ground. It would be the same as the vehicle ground, but the alternators would not be interchangeable.

You are correct about the load balance, though. In this case, there would be no imbalance since the 12V alternator would keep the 12V loads satisfied. Essentially, that's how I modified my old M1028A3's 200-amp system to fix the problem.

 

[tomc]

Have a similar problem with my M1010. Drove it home from AL, ran great. Had problems with alternators, bottom one needed repair. Both batteries were checked out and found to be good. Can charge them up and put back into vehicle. Seems to have a fuel problem, listed under that thread. But if batteries sit over night they loose all charge. Any ideas?

thanks,

Tom in TN

 

[tomc]

Have a similar problem with my M1010. Drove it home from AL, ran great. Had problems with alternators, bottom one needed repair. Both batteries were checked out and found to be good. Can charge them up and put back into vehicle. Seems to have a fuel problem, listed under that thread. But if batteries sit over night they loose all charge. Any ideas?

thanks,

Tom in TN

 

[Michael]

The M1010 charging system rarely works correctly. I worked on mine a long time and finally got it to charge reasonably well but it would still go dead if it sat a couple of days. That was with new batteries. I ended up just unhooking the front ground at the end of the day.

I would do the orange wire conversion which is on this site in the resources.

also search for DUVAC in the CUCV forum.