M37 Distributor and coil

mdainsd

Member
193
14
18
Location
San Diego, CA
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

New member
3
0
1
Location
McDonough, GA
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

Member
193
14
18
Location
San Diego, CA
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

Member
86
54
18
Location
Monkton, VT
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.
 

M37keppy

Member
51
19
8
Location
Eldridge, Iowa
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.
 
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