M37 Distributor and coil

[mdainsd]

Things I have learned along the way about M37 distributors, well actually most M series distributors.

The two vent lines are not there to cool the coil. In those tiny little lines with no forced flow you wont get enough air to cool a gnats ass. They are there to strip condensation and ionized air out of the distributor. The air gets ionized by the high voltage discharges between the tip of the rotor and the six contacts that feed the plugs. Remember there is no physical contact, the spark jumps that gap. As the air becomes more ionized it starts to become conductive and misfiring or no firing will result. We all know what condensation will do in a distributor. Heat is removed by the fins on the part of the distributor that encircle the coil. Notice the tight fit of the coil? Thats why.

Next the filter capacitors: The filter capacitor is not to be confused with the condenser across the points. Early trucks have no filter capacitor in the distributor, theirs is in a box mounted on the firewall next to the horn. Later trucks have the filter cap built into the connector that one connects the 24V ignition cable to the distributor. The early ones were prone to failure. The later ones also fail with regularity. All my M stuff I have removed the built in type filter capacitor completely. For originality on my very early M37 and M38 i retain the large firewall mounted filter, but I have spares.

 

[RayJH]

My original coil had a disc under it that I think was a resistor. That coil was cracked so I put an aftermarket coil in. I am on my third after market coil. Do these need a resistor? Are these coils made for 24 volt?

 

[mdainsd]

My original coil had a disc under it that I think was a resistor. That coil was cracked so I put an aftermarket coil in. I am on my third after market coil. Do these need a resistor? Are these coils made for 24 volt?

The resistor was in some distributors. I cant remember for sure, but I think mainly in MUTTS. The aftermarket coils from china are junk. No getting around it. They can usually be weeded out by their chrome like appearance. Unfortunately you need to hunt down NOS coils which are starting to become scarce. Pay the price once and it should last a good long time. Just my 2 cents.

 

[John Mc]

I read somewhere that the aftermarket coils are often just a bit too short, so they don't make good contact to conduct the heat away. One fix some people use with some success is to put a metal disc in the bottom to help take up the space (the recommendations I saw were to coat the disk in some heat-conductive past prior to installing).

I'm new to this, and have not run into any of this myself. Just passing along what I read. I'd include a link, but have no idea where I saw it now. Hopefully someone more knowlegable than I will correct me if I'm wrong.

 

[M37keppy]

I read somewhere that the aftermarket coils are often just a bit too short, so they don't make good contact to conduct the heat away. On efix some people use with some success is to put a metal disc in the bottom to help take up the space (the recommendations I saw were to coat the disk in some heat-conductive past prior to installing).

I'm new to this, and have not run into any of this myself. Just passing along what I read. I'd include a link, but have no idea where I saw it now. Hopefully someone more knowlegable than I will correct me if I'm wrong.

That fix was posted on the g741 web site with photos.

 

[joseph m37]

I have a 1954 M37, stopped running, i believe its the coil.
I am concerned about the gunk that i found in the distributor coil area when i removed the distributor cap.
This must come through the vent lines. Is it OK to leave the vent lines off the distributor and just connect them together rather than running them through the distributor. I do not run in mud or water. Any suggestions on best way to handle the two openings left on the distributor?

Thanks

the vent lines running to the distributor are there for a reason, they keep the coil from overheating ,your coil is in a enclosed case and there is no way for it to dissipate the heat, leave the lines connected to the dist.case,in the correct position also

 

[joseph m37]

I read somewhere that the aftermarket coils are often just a bit too short, so they don't make good contact to conduct the heat away. On efix some people use with some success is to put a metal disc in the bottom to help take up the space (the recommendations I saw were to coat the disk in some heat-conductive past prior to installing).

I'm new to this, and have not run into any of this myself. Just passing along what I read. I'd include a link, but have no idea where I saw it now. Hopefully someone more knowlegable than I will correct me if I'm wrong.

yes thats true, the coil needs to dissipate the heat it generates, the paste or a metal disc would help

 

[joseph m37]

My truck, since I have had it, has not had the vent lines to the distributor hooked up at all. The ignition has never given me any problem what so ever except for one time the points needed re-gaped. I would have to agree thru experience that the convection of the distributor case is cooling enough for the coil. Or maybe I am just lucky. If it wasn't for bad luck I wouldn't have any luck at all so I doubt it is luck.

leave those vent lines connected, they are there for a reason to cool the coil

 

[joseph m37]

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The M37 ignition is a bit different than the M35 but I still believe that the case of the coil will dissipate more heat than the two vent tubes. I just don't think that you will get that much airflow through the tiny vent tubes. I don't know who is supplying Charle's ignition module but it looks like Pertronix. If it is Pertronix's standard Ignitor, you need to make sure that you don't exceed the maximum current.

the vent lines are there for two reasons, for underwater operation to keep air flow and keep the unit waterproof, but also for cooling,they were designed to pull outside air into the housing thats why they have different ends on them, take you distributor out and service it, clean it, check for worn bushings, gap the points check all the wires,we've had some wee the wires were bare,the insulation deteriorated from age,go through it, they work fine

 

[joseph m37]

The coil is cooled by convection and radiation from it's case; not by the vent lines. A drawback of the vent lines is that they can allow oil mist inside of the distributor which is detrimental to point life. NAPA has a pipe thread breather which can be screwed into the distributor. This is what I did on my M35.

if your getting what you cal oil mist in your distributor than take it out and put new seals, no oil mist gets into the distributor you have a oil breather tube that should be connected removing vapor,that is your crankcase vent tube which a lot of " know it alls" remove

 

[joseph m37]

I have an ignition problem, symptoms were the engine runs great for a few minutes then shuts down, no sputtering like its running out of fuel. Seems there is no way to get a coil tested if it malfunctions because of heat. I installed a new coil and with a wire from the coil to the engine block i get a nice white spark at least a 1/4 inch. when i put the dist cap back on i get nothing thru the spark plug wires.
Can a condenser cause a problem like this? Again this engine was running perfectly up to now and always started very quickly.

Thanks

if the if the the engine dies after getting warm without any erratic behavior, it sounds like a coil issue,coil has two sets of windings of different gauge,when the coil gets hot the windings separate killing the motor, when the engine cools down they come back together and your engine will probably restart,pull the coil and have it tested with a ohm gauge check resistance,any question replace it if it has never been ,,dont ever leave the ignition switch on either,this is energizing the coil and will burn it out

 

[joseph m37]

I have a 1954 M37, stopped running, i believe its the coil.
I am concerned about the gunk that i found in the distributor coil area when i removed the distributor cap.
This must come through the vent lines. Is it OK to leave the vent lines off the distributor and just connect them together rather than running them through the distributor. I do not run in mud or water. Any suggestions on best way to handle the two openings left on the distributor?

Thanks

no it did not come through the vent lines unless the crankcase ventilation tube was disconnected or plugged which i have seen done,remenber those distributors haven't seen service since the military,mostg guys shy away from pulling the distributor,one bolt,disconnect the cap put it on the bench