Help! I'm burning up coils in my M43!!

[zak]

I have one of the coils with the separate resistor. I'll post a picture this afternoon when I get home.

 

[m37brat]

If your getting 6ohms means the resister is letting to much voltage to the coil/windings, this has been a ongoing problem with imported coils, if this was me I would ad a external resister to the dist power lead this will give lower voltage to the coil to which it will run cooler. This symtom was quite common back in the points and condenser days of automobiles, I had a 1968 Olds F85 that the coil had a bad ( internal ) resister, when it got to hot the car would shut down and about 30 minutes later ( after coil cooled down ) it would start right up and run like a champ. Alan Bowes did a great write up on this problem with the M-37 coils and if I can find page 2 of that article I will be able to tell you what ohm resister to buy/add to the power lead

P.S. TGP no luck ( yet) on the stacked coil pic

Bill, is the Alan Bowes article on Steel Soldiers? I would like to read it so I can learn a little more.


As a side note, the first time I replaced a coil was on my M37 which had the "wafer" onder the coil.
Thanks, Jim

 

[zak]

Original, made in Toledo.

 

[Bill W]

Bill, is the Alan Bowes article on Steel Soldiers? I would like to read it so I can learn a little more.

Jim
Alans article was on his long gone website "MV Central" this was going back almost 12 years

 

[Oldfart]

Zak's photos are interesting. I have never seen the extra resistor button before. I checked the ORD number on the coil and it comes up as a coil for a Jeep 715. I know the Dodge M37/M43 distributors are very similar and I suppose the coils will interchange. In fact I think the only real difference is the distributor shaft and mounting plate. My manuals show the M37/M43 coil ORD number to be 7374882.

 

[Oldfart]

A quick comment about the vent/cooling lines. Since the system is under water, the distributor is sealed from ambient and depends on the vent/cooling lines attached to the carb air horn. The major purpose of the lines is to sweep the air across the points plates and around the coil. Fresh air as it were will evaporate condensate that would collect on the points shorting out the make/break of the spark generation. I have always assumed there was a cooling aspect as well as evaporation of moisture and exhausting of crankcase fumes because of the placement of the lines on either side of the coil.

I don't think we have moved very far in solving Brat's problem. Either he has a batch of bad coils, or something in his system is taking his coils out or his problem is not the coils, but something else.

 

[m37brat]

I appreciate all the input and I still have a few things tom check. I have a coil coming from another supplier and will be checking the ohms to see if there is a difference from the ones I have. I am also trying to find a resistor that will work to see if that helps. I did take a reading at the batteries and I am getting a reading between 27 and 28 volts which may be part of the problem. Is there an adjustment on the regulator I can make to reduce the output?

Thanks to all for the help.

Jim

 

[Oldfart]

I don't know if the electronic regulator is adjustable, but the old contact style is adjustable. How long does the voltage at the batteries hang around 27/28 volts? This is 13.5 to 14 volts per battery and what might be expected just after the engine starts running. After a few minutes, the voltage should start dropping as the batteries recover their charge after the drain of starting. If the voltage remains that high all the time, the batteries will start to boil and lose water. Having said that, the 27/28 volt range is the top of what you want to see and that should drop to around 25 volts if everything is charged up and there are no accessories drawing current.

 

[m37brat]

After reading everything all of you guys had to say I think I've settled on my solution. I checked the volts running through the line going to the coil and I am getting 28 volts. I think this may have been a problem for a while on this truck. The truck was owned by a fire department in Vermont and it appeared that they took pretty good care of it. When going through the restoration I found that the line from the switch to the coil was cut and connected with soder-less connectors. It's a good chance that they used a resistor in the line at some point so I am going to put a resistor in the line and a fellow who has worked on more of these truck than you can imagine is going to show me how to adjust the regulator. With a little luck and the grace of God she will be back on the road and will be going to a couple of fund raisers next month.

I really want to thank everyone who took the time to help and will be letting you all know how everything turns out.

Thanks, Jim

 

[M371954]

Jim, did your solution work? I seem to be having a very similar problem. Thanks, Mark

 

[m37brat]

Jim, did your solution work? I seem to be having a very similar problem. Thanks, Mark

To be honest Mark I'm not sure. It checked we the guy that I bought the truck from and he told me he put the cut in the line to extend the wire when he redid the front wire harness. I decided to put the resistor in the line and I also remove the large plug on the top of the distributor in the summer. I also found that the vent line that runs to the gas tank had a serious problem. The valve at the end of he line, at e tank was bad so the carb was being chocked of from the vacuum being generated in the tank. I fixed that problem and now everything seems to be ok. Knock on wood, hopefully I'm home free. I've done several parades this past summer and had no problems.

 

[Bill W]

You should have a vented fuel cap on the M-37 like the one inthe pic, make sure the ( fording ) valve in the cap is open ( see pencil ). The little 1/8"vent line that runs from the tank to the airhorn is for when your fording and really doesn't vent enough when your out running high rpms.

 

[Oldfart]

There have been a number of times I have found M37's (same fuel and electrical as M43) stranded on a high Colorado mountain peak thinking they were vapor locked. In fact they had their gas cap's screwed all the way tight not allowing any air to the fuel tank. The Fording Systems had a pull cable on the dash that switched a valve on the vent lines to the airhorn so some air could relieve the fuel drawn from the tank by the fuel pump when under water. Fairly quickly, the military dropped the complete Fording System from their requirements (like the fuel priming system as well). However, portions of the Fording System remained a part of production for a while. The vent system to the coil does not have any fording valves and essentially functions all the time. It is important to have the coil vent lines attached to the air horn in the proper locations as there is a vacuum/pressure differential that pushes/sucks air around the coil. If you remove the brass plug on the top of the coil/distributor assembly, that allows the pressure differentials to be satisified to ambient through the plug hole and may actually result in less cooling air around the coil. All of that said, I have also seen a distributor with all the vent lines capped off that ran fine and according to the owner had not given him any trouble.

 

[Gamagoat1]

One thing I've not seen mentioned here. These coils come in 12 or 24 volt. It's normally stamped in the side or bottom. This would explain the diff in resistance across the leads of the coil. I have both and they look exactly the same except for the stamping. I burned up several 12v coils before I opened my eyes and looked.

 

[PappyFrance]

24V coils overheat and die. Help please!

I have a Hotckiss M201 which had a mickey mouse 12V coil outside the distributer. I thought I would restore it to 24V in distributer system. Since then I have burned out 3 coils in short order and now have a 4th that is dying. I put 24V pertronixs solid state points after the second and it ran great, but those burned out with the last coil ater a short time. Put the old points back in and a new coil and it ran great at first. Now it is loosing power again. Coil is always hot. Maybe the last owner knew something I didn't.

I have read a lot of people have this same issue, but no clear solutions. Any ideas? Part numbers, pictures....

 

[M371954]

I finally rooted my problem in the voltage regulator. Once that sucker was replaced, my system has been rock solid.

 

[PappyFrance]

I finally rooted my problem in the voltage regulator. Once that sucker was replaced, my system has been rock solid.

I put an electronic regulator but no efffect except a lighter wallet.

 

[Gunnermac]

I ran into the same problem with a M38a1 jeep in 24 volt. If the ignition switch is left on for any time it will fry the coil. Added to this the coils sold on ebay are for the most part chinese, and less than useless., particularly the pretty chrome ones. NOS are hard to find, but worth the effort. I bought the last NOS one from a fellow in North Ga. that specializes in jeep parts. I don't think I am supposed to add links, but PM if you want the name.

 

[mdainsd]

Oh my goodness. So much information and not all correct. The coils with the resistors were manufactured that way for 24V distributors before a true 24V coil was developed. Most of them are long gone that why your rarely see them these days.

The vent lines are to remove ionized air from the interiour of the distributor and displace moist air. One look at how the coil is housed tightly in its bore will show you that cooling through 1/8" ID lines with no force isn't going to cool diddly. Hint: that is what the fins on the distributor housing are for, notice where they are?

Next, an earlier poster mentioned checking the input filter capacitor, they get old and break down causing symptoms that seem just like a coil problem. That filter is hard to check, eliminate it, it is not required. Take it out by removing the four screws, remove it from the inside of the flange, then run a new wire direct from the connector pin to the coil.

The early trucks did NOT have an external resistor mounted on the firewall, that thing is a large filter capacitor, that as time moved on was replaced by the filter capacitor I mention in the paragraph above.

An M37 in 70 ish degree weather with the engine at high idle should show about 28.6V all the time give or take a couple of tenths. It does NOT drop down as the batteries are recharged from starting. Nothing more than a digital multimeter is needed to test this. Check right on the battery terminal, no need for disconnection of this or that.

 

[Bill Nutting]

Get rid of the filter capacitor! Go back to Billw’s post and do what he showed you in the photo. He gave me the same advice about twelve years ago and my M37’s “bad coil” is still going strong. I have made that mod on my wife’s M151 and all of my friends M series vehicles.