‘77 MUTTnot charging batteries

1959 - 1978, M151, M151A1, M151A2, Technical questions and discussions, regarding anything related to the M151.
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shawnhoag
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‘77 MUTTnot charging batteries

Post by shawnhoag » Sun Jun 13, 2021 5:15 pm

My ‘77 MUTT has the 60 amp, 3 pulley alternator. 2 of the belts are tight enough. One is looser. The truck was starting up ok, but lagging some. It has 2, like new, Interstate 51R batteries. All cables and wires are good and tight. The vacuum lines are older, but pliable. It seems when it heats up it is not starting easy. The other night we had a gathering, and I gave a few rides, a couple miles each. On the 4th or 5th ride, in a 2 hour period, it would not turn over enough to start. We pushed it and pop started it. Fast forward two days, and it will barely crank over enough to turn the engine over once, or half a time. Still pop starts and runs great. I’ll be honest, I have never owned a jeep this new. I’m used to points, not “solid-state” or whatever it is called, ignition. Any ideas?
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Re: ‘77 MUTTnot charging batteries

Post by markrdje » Sun Jun 13, 2021 6:32 pm

Maybe the starter is going bad?If battery is good, then maybe the connections/cable are not good?
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Re: ‘77 MUTTnot charging batteries

Post by shawnhoag » Sun Jun 13, 2021 6:33 pm

Could be. What’s the test for it?
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Re: ‘77 MUTTnot charging batteries

Post by muttguru » Mon Jun 14, 2021 1:02 am

Shawn,
go right to the core of the problem.
First things first. Look at the diagram below and make sure your batteries are wired up correctly. Make absolutely certain that all the battery terminals are clean and that the battery terminal clamps are clean and tight. Check that the inter-battery cable is clean and tight at both ends. (Lug 2 to lug 3)
Make certain that the cable that goes from Lug 4 to ground (at the wall of the battery box) is properly attached to the wall.....there should be star-washers in place and there should be no paint or corrosion on the wall of the battery-box in the area where the cable attaches.
There should also be a cable from the side of the bell housing to the horn mount. If the engine has been taken out, reinstalling that cable is sometimes forgotten. Without this, the engine will struggle to start.
When you are sure that the cables and grounds are in good shape, here's what to do next.

Get yourself a multi-meter for checking the output of the alternator.
1. Take out the passenger seat;
2. Remove the battery-box cover;
3. Start the engine (or bump-start the vehicle if the batteries are flat);
4. With the engine running, use the meter across the two batteries... one meter probe to Lug 1, the other meter probe to Lug 4.
5. You should have a reading around 28 volts.
6. If you get a reading of 24 volts or less, the alternator is not working.
Get back to us.

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Re: ‘77 MUTTnot charging batteries

Post by Rickf » Mon Jun 14, 2021 5:28 am

I did not see any mention anywhere in that first post of you testing the voltage of the batteries? Were they at least 24 volts at all times and close 28 volts when running? You need to check voltages before throwing a ton of other stuff into it.

And do NOT go by what the gauge on the dash says! They are notorious for being off.

And as far as the point vs. electronic ignition, if your batteries were so low you had to push start it then if you had electronic ignition it still would not have run. Electronic ignition will start to die around 18 volts. You could very well have points in this vehicle. It is the exact same distributor that was used in all M151's and the same exact distributor used in all M series vehicles with different adapters for the drives to match the motors they were in. So a M38 had the same distributor.
1964 M151A1
1984 M1008
1967 M416
04/1952 M100
12/1952 M100- Departed
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Re: ‘77 MUTTnot charging batteries

Post by shawnhoag » Mon Jun 14, 2021 1:24 pm

Thank You both! My job keeps me extremely busy, but I will get to it in the next few days, and I WILL get back to you guys so the next guy gets the knowledge.
Thank You,
Shawn
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Re: ‘77 MUTTnot charging batteries

Post by shawnhoag » Mon Jun 14, 2021 2:33 pm

I had a few minutes to spend tonight. My distributor DOES have points. They and the rotor were clean. I have the batteries ready to charge tomorrow, so that I can check the voltage before and after starting it. The cables are all clean and tight. Batteries are hooked up according to the chart.
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Re: ‘77 MUTTnot charging batteries

Post by shawnhoag » Tue Jun 15, 2021 5:27 pm

Update:
I put some time in tonight. I took all the electrical connections apart that have anything to do with grounding, and cleaned paint off, mild corrosion, and tightened a few loose connections. I full charged the batteries. The MUTT spun over better than it ever has, and fired right up. I tried it several times, and it spun over great and started right up.
I will be checking the voltage tomorrow, as I didn’t have a voltmeter today.
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Re: ‘77 MUTTnot charging batteries

Post by shawnhoag » Wed Jun 16, 2021 9:52 am

Update:
Both batteries are at 12 volts separately. Running, and with the voltmeter across the two lugs that DO NOT connect the batteries together, it is at 25.1 volts. This has the 3-pulley, 60 amp (I am assuming) alternator. I am also assuming since it is at 25.1 volts, that it is not working. My question is, are there any circuit breakers or anything else that needs to be checked prior to assuming the alternator is bad?
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Re: ‘77 MUTTnot charging batteries

Post by Rickf » Wed Jun 16, 2021 10:30 am

Nope, alternator is not charging. Most likely a bad regulator but there is an adjustment screw you can try to adjust. If this was working before though I would say don't play with the screw since it does not go out of adjustment, that is an initial adjustment thing and once set it is done. If it was working before and not now then something went bad. There is one connection you probably did not clean, that is the #5 wire where it goes to the starter switch on the floor. But before digging that out of the floor, with it running check the voltage at the #5 terminal on the alternator and see if the voltage there is higher than the voltage at the batteries.

And, Are both batteries equal in charge when not running? ie, 12.2 volts on both batteries. You said both batteries are 12 volts separately but a fully charged battery is 12.7 volts. If they were actually reading 12 volts then you could have one or two bad batteries.
1964 M151A1
1984 M1008
1967 M416
04/1952 M100
12/1952 M100- Departed
AN/TSQ-114A Trailblazer- Gone

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Re: ‘77 MUTTnot charging batteries

Post by shawnhoag » Wed Jun 16, 2021 10:38 am

Rick,
I did take the floor starter switch completely out, took all 3 cables off, and cleaned them. The batteries were at 12.6 volts each, my bad for saying 12 volts. I don't know that it WAS working properly before. I just bought the MUTT, and the owner told me to pull one lug off the battery if I was going to let it sit awhile. He said it would discharge. I have only driven the MUTT a few times, so I have no idea if it was previously charging, or if he had charged the batteries just prior to me buying it, and they ran down during the times I drove it. I will do the #5 wire test. If it is a bad alternator, do "normal" electrical shops rebuild them?
Thank You very much for the help!
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Re: ‘77 MUTTnot charging batteries

Post by shawnhoag » Wed Jun 16, 2021 10:40 am

Also, what is the small box on top of the alternator? I see a few alternators listed on Ebay, but none have that box attached. Pardon my ignorance on this!
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Re: ‘77 MUTTnot charging batteries

Post by Rickf » Wed Jun 16, 2021 10:42 am

BINGO!!!!! If he pulled the battery cable off while it was running he fried the alternator! That was something you could do in the old days of generators but NOT with an alternator. If you are lucky it only took out the regulator, if not it took out the diodes. The good part of all of this is all the parts are available to rebuild the alternator from Southern Automotive.

I don't have a picture of yours but the only "box" that should be there is the flat area where the wires go in.
1964 M151A1
1984 M1008
1967 M416
04/1952 M100
12/1952 M100- Departed
AN/TSQ-114A Trailblazer- Gone

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Re: ‘77 MUTTnot charging batteries

Post by Rickf » Wed Jun 16, 2021 10:45 am

It is sounding like maybe this is not a military alternator.
1964 M151A1
1984 M1008
1967 M416
04/1952 M100
12/1952 M100- Departed
AN/TSQ-114A Trailblazer- Gone

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Re: ‘77 MUTTnot charging batteries

Post by Rickf » Wed Jun 16, 2021 10:46 am

Check your PM's
1964 M151A1
1984 M1008
1967 M416
04/1952 M100
12/1952 M100- Departed
AN/TSQ-114A Trailblazer- Gone


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