24 volt to 12 volt swap M38A1

I decided to do a 12 volt conversion......The factory wiring was shot.Looks like mice had a great time eating it.

Im Actually going to Rewire the entire jeep but I have a few questions.

What can I reuse and what will I need to get this done Cheaply

I think Ill need the following

Starter.............
Distributor........
Alternator..........

I think I can make a GM alternator work...
Do any of you know of a Cheap replacement starter and distributor?

I was thinking of using a painless wiring kit.

 

12 volt gauges and you can use the old gas tank sending unit. I'm not sure on the motor stuff. My motor was changed.

 

INTEGRAL COIL

The last military distributor in a Jeep I worked on had the coil inside the distributor, somewhat in the fashion of a mid-80s HEI system. (Waterproof Distributor)

Of course, there may be other kinds of distributors that were used in the military jeeps. If it doesn't have waterproof (screwed in fittings on the spark plugs and distributor), it isn't military. (civilian was swapped in).

I don't recall, but I will make an educated guess that the coil is not a 12V coil (for use without dropping resistor) or a 6V coil (used with dropping resistors). It would be a 24V coil, or have a dropping resistor that would be set for a 24V system.

As for the wiring harness, I believe that Walck's carries ones for the M38A1. I know there are others that do also. As for the "Painless" wiring harnesses --- I have never personally used that brand, but will tell you that in my experience, it is "painful" enough just swapping out a stock harness with a stock harness. Just be sure to NOT use crimp-on terminations unless you solder and heatshrink them. (Think of how reliable the stereo installations are that are done by high-schoolers using crimped on/wire-nuts, etc. -- or do you want a jeep that dies, shorts, or starts electrical fires?)

 

I've been wondering about the best way to do the same thing. My M38a1 currently has no wiring system!

 

Mine has all the waterproof conectors.
I think Ill just have to run an external coil .

What about the starter you guys think the 24 volt will work on 12?

 

A 24V starter will work fine under three circumstances:

1) You have 2 12V batteries in parallel and you use a series/parallel switch to present 24V potential to the starter. (Actually the starter is probably designed to run @ 18V as 12V systems are designed to operate at 9V.

OR

2) Your engine starts so easily that it will reliably "light" with the engine turning over at 1/2 of the designed starter RPM. This assumes that you will not operate in a cold climate (where the chemical nature of a battery is inhibited and less voltage potential is available). And it also assumes that you will never have a hot start problem.

OR

3) Remembering that higher voltages do not require as large a gauge of wire as a lower voltage, the starter will likely not be wound with the same gauge as a 12V starter. As a result, the amp load in the windings will be considerably greater using a 24V starter in a 12V application, than the proper windings for a 12V application. This means more heat, and shorter life. (assuming it will even turn over fast enough to reliably start the engine)

Further, as the amp draw of the starter will be higher (because of the smaller windings) it will require a larger capacity battery to turn the starter over for any length of time. (Remember that heat generated by insufficient voltage will cause the resistance to increase, further increasing the amp draw of the misapplied starter).

So, your third option would be to have the starter rewound for 12V (or purchase a 12V armature) and replace the 24V field windings with 12V windings. In other words, keep the starter case and drive and put all new guts in it.

I've laid out the theory and the reasons why a 24V starter should not be used in a 12V system. Of course, you can call any starter rebuilder or electrical engineer, and they will tell you the same. And trust me, a lot of what I laid out is what I learned after trying to figure out why I can't get something to work.

BOTTOM LINE:

NO, it is NOT practical to use a 24V starter in a 12V system. Were you talking about using a 28V starter (some military aircraft usage) in a 24V system, the answer would be "maybe," but that is not the issue here.

BUT, REALLY, CAN YOU USE A 24V STARTER IN A 12V SYSTEM?

ABSOLUTELY. Don't let my comments stop you from experimenting. One method that you could use would be to use your 12V system through an inverter (better be a big one), and doesn't really need a good one (a cheap one that puts out a "square" sine wave would be fine). Run it through a really big transformer to drop it to 24-30 volts, and then put some huge diodes on it to convert it back to DC, and then run those leads to the starter. That WOULD WORK. However, you would probably have to have a bank of 12V batteries to run that system. Yes, it can be made to work, but the more important question is: "Does it make sense?".

 

You can buy 12 volt coils that fit the military distributor. They are at least available at Rapco & Midwest Military.

The 24 volt water proof system is much sturdier than the civvy 12 volt system and the 24 volt spins the engine much better in cold temps then the 12 volt. But as mentioned above depending on the state of your 24 volt system it may be cheaper to go 12.

Gages on the A1 are all electric and must be changed. Their senders are matched to them and must be changed. The lamps, generator, regulator horn, and starter must be changed.

The later 12 volt F134 starters MDM6005 and MDU-7004 will work and the later 12 volt generator/regulators for the 12 volt CJ3B and CJ5/6 will work. If you are going with the 12 volt swap the Alternator is a much better choice over the generator.

I see the one person mentioned keeping the 24 volt fuel gage sender. Yes it can be kept but just like the water temp and oil pressure senders it will give erroneous readings when used on 12 volt. The fellow above probably just learned to live with 1/4 = empty and 3/4 = full. I would buy a good 12 volt after market gage with matching tank unit and use direct reading mechanical gages for oil press and water temp.

 

I'll trade you. I have starter, generator, regulator, lights, dist. all in working condition. PM sent.

 

From what I'm reading you'll probably be changing the distributor. Might I suggest that you go with electronic ignition? It's only a few dollars more and you never have to change points again...

 

I'm here to agree with the post about considering keeping the 24volt system. The components are all super high quality and reliable. Totally sealed, never get wet or dirty, last forever. Zero maintainance. Easy to locate parts, since they were all the same from year to year.

Another thing is that military jeeps were usually "surplused out" with less than 30,000 miles.

I have 6 and 12 volt CJ's but I love my M38A1 too. If the stuff was cheaper every jeep ought to be built to the military standard.

Switching over to 12 volt makes parts cheaper, but will be a lot of work and expense up front.

I think someone told me once of another miltary distributor/coil that operates at 12volts, but fits a jeep F-134. I forget but maybe it is from a gamma goat or something like that?