76 M151 A2 suddenly dies

[Peteda2]

Hi all, My 1976 AMG M151 A2 suddenly will not start. It started and was running good mid week, but yesterday when I tried to start it it will not turn over. I heard a spinning sound but the engine will not turn over. I charged the batteries yesterday and both are fully charged (according to the green light of the charger) , but when I tried again today same thing. Engine will not crank, I heard the spinning sound with the first attempt, but with the second attempt nothing, not even the spinning sound. The voltmeter on the dash was yellow to green before the first attempt today, when I press the starter button it will swing to the far left and back where it was before when I step off the starter but nothing happens. I should add that the batteries are the 2HN military type about 5 or 6 years old since installed, and I do keep an eye on them adding DI as needed. Any help or advise will be very much appreciated.

Also I live in northern New Jersey, in Wayne to be exact. If anyone from the group can recommend a mechanic who is familiar with M151s in the general vicinity please let me know.

Thanks

[fowlercal]

My first GUESS is the starter is not engaging the flywheel, or the Bendix is stuck against the flywheel.
I’m sure you will get more details soon from more experienced mechanics when they see your post

Cal

[glcaines]

If your 2HN batteries are 5 - 6 years old, I would go ahead and replace them with new batteries. I eliminate the batteries before proceeding further since 5 - 6 years is about max for batteries. You are going to need them soon anyway. I would replace them with 51-R AGMs. Brackets are available to secure them.

[rickf]

If the volt meter is swinging far left when you hit the starter that tells me the batteries are not handling the load. Most likely you have one bad battery that will not carry a load. One thing to check before totally condemning the batteries is take all the cables off the batteries and clean the terminals and the connectors and reinstall them If same thing happens then bad battery. You can put a volt meter between the two terminal of each battery to see which one is bad. But when replacing you always want to replace in pairs.

[rickf]

There is a guy who lives in Morristown and his username is NJJeeper. I have not seen him on here is a while, he may be on the G503. He has built several really nice military vehicles including a 718 which I think he still has. And also a Ferret.

[Peteda2]

Hi all, thank you for the quick response. I will concentrate on the batteries first and take it from there. The voltmeter on the dash does swing all the way to the left when I hit the starter button. I will take them apart clean the posts and connectors and see if it makes a difference. The batteries were installed together in mid 2018. When I measure voltage across the 2 of them I get 23.5V a bit less than 24 V. Is voltage the only indicator of life or cranking power or other things are important? I understand that 51R is the correct replacement type/size if I have to get to that.

Thank you all again.

[kmam]

You really need to measure the voltage under load to test the batteries or get a proper battery tester - there are many available these days for a good price. The simplest way to check is to have your voltmeter connected to the batteries when you press the starter. You will probably be horrified to see how much the reading drops, indicating a bad battery - this, of course, is what you are seeing with the meter dropping to the red. You can then connect the voltmeter to each battery in turn and press the starter to see if it is one or both batteries that are dead.

[Horst]

at work, I am not allowed to start below a battery voltage of 22V. Normally the battery voltage is between 23 and 26V with the engine not running. When I hit the starter button, voltage drops as much as down to 18V, if it drops further and below 16V, I will have to abort the start.

Once the engine is running and the generator turned on, voltage will be pretty much exactly 28V.

Now all this is no car or jeep, but an indication what kind of voltages to expect with a 24V system.

[svramselaar]

hi

if your battery`s has caps on the cells you can open them all
them start without contact or try to
look inside the battery cells is if one bubbles this one is bad

george

[rickf]

The 2HN batteries are very old technology and as such they are also not very long lived. If they are 5 years old they are about done, especially if they sat for long periods without charging. This is where a trickle charger/maintainer comes in. But really, the 51R batteries nowadays have twice the starting power in one battery than two of the 2HN's. Lifespan is roughly the same if they sit without a maintainer on them though. AGM batteries are the cream of the crop, but also priced like it. You are looking at 250.00-350.00 for each AGM battery. Considering they generally last twice as long as a standard lead acid battery the math works out in the long run but that initial price is beyond my budget. I have three diesel pickups using two batteries each, two military generators and three military vehicles all using two batteries each. 16 batteries!!!!! Plus my two regular cars. So 18 batteries total.
You could tow it down here but that would be kind of excessive for a battery issue. And I have nowhere to store it so you would have to tow it back at the end of the day.

[Hambone]

I can't spend $300 on a battery, I have had good luck with 2 sets of these, one set is going on 3 years old.
https://www.autozone.com/batteries-star ... 1r+battery

[glcaines]

I spent $255.00 each for Super Start Platinum AGMs for my M151A2 at O'Reilly's Auto Parts recently. I like the AGMs not only because of the extra power but also they don't cause rust and corrosion in the battery box. O'Reilly's also gives a 10% discount to veterans, so my total price was ~$459.00 before taxes. I've been getting more than 10 years with Super Start AGMs in my F250s, and the last AGMs in my M35A3 deuce went over 10 years. I also have Odyssey PC2250-SI AGMs in my FLU419. The Exide AGMs in my MEP003A lasted over 10 years as well and it now has Odyssey AGMs installed. I realize the price is high at the beginning, but the dependability and long term performance is worth it to me.

[Peteda2]

Hi all,

Just a quick update, that it was the batteries after all. I replaced both with new AGM batteries as suggested by the SMEs, and it started right up.
Thank you again for your valuable advise and collective expertise!! I will pay more attention to my dash voltmeter now, specially if I crank the engine and it swings all the way into the left

[rickf]

Glad to hear you got it going. I don't think you will have any battery issues now for many years. If you leave it sitting for long periods it is still a good idea to have a battery tender on them. You can get a 24 volt tender which would be good if you are starting out with new batteries like you are. Or you can get two 12 volt models and have one hooked to each battery. The tenders come with the wiring to permanently attach the charging wire to the battery and they have a plug on that wire that plugs into the tender wiring. That way you do not have to have the actual tender hooked up while you are out and about.

[kmam]

Ah, Rick, another point of difference between US and Oz! A battery tender here would probably be something to carry a bunch of batteries whereas a battery charger would get their voltage up to the correct level