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My '41 has both Electromatic Clutch and OD. Both work well. Recently, the OD stopped engaging.
I found that the EC wire on my governor was quite loose. It is held in by a long screw with a bolt that tightens the wire. I tightened both the screw and the bolt to secure the wire. That did not help. I changed out for the governor on my spare OD, which works, but the weights are different and the engagement speed is way too low.
I came to think I maybe got the screw in too far and shorted the points.
One of my manuals says to test the governor by hooking up a test lamp. The lamp should light at the EC terminal and not the AD terminal. So, I did that, screwing in the screw only until I got the EC terminal to light the test lamp. The AD terminal does not light it.
That too does not work once in the car (with the original governor and correct weight set).
Doesn't appear to be a good way to test the AD engagement out of the car.
Any thoughts on why this doesn't work once I get the test light to light?
The Electromatic clutch does work with either governor.

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The governor only has one set of contacts and it switches state at speed. EC is the normally closed contact while AD is the normally open contact. The little strap from the ground point at the screw goes to the common. At speed EC opens to disable that option and AD closes so the relay will power up and allow the OD to be prepared to engage.

I believe about the only way to adjust would be to rig up something like a drill motor to spin the governor at a constant speed and adjust the screw while it is spinning. It would also need some sort of tachometer and Amazon does sell a few inexpensive reflective tachs that should do the job. The difficulty is knowing what RPM would equal the speed you want it to change.

I believe one of the posters on this forum has a speedo repair shop and perhaps he would know what RPM would be needed to make the speedometer read in the 20mph range which is where Packard had most ODs wanting to come in. The governor and speedo both use the same drive gear off the trans shaft and while there might be a slight difference in governor vs speedo RPM because of the different speedo gears available for axle ratios they would be close. Packard did spec a several mph range when ODs would typically come in.

Without knowing the RPM needed it would be a difficult and time consuming trial and error job to try and guess where to adjust the screw.

Good Evening...I'm wondering if the little paul that needs to move to engage the overdrive has become dirty and there is a bit of dirt or some such binding it...Ernie in Arizona

Ernie, little Paul? How cute! Probably should be little pawl. (Sorry, I couldn't resist!)

Found a couple of forum references including one on the Stude forum that said the majority of speedometers of that era were calibrated to require 1000 RPM to read 60mph. If this holds true for Packard (and I do not know if it does because there were two or three other common RPMs used) then it is a starting point and if it is a straight linear ratio I would say for a reading of 20mph it should need around 330 RPM.

You could run the governor somewhere in the 300-350 range and adjust the screw so the contacts switched. Try it out and if not where you want it at least you would know what RPM you used and a good guess as to the RPM needed so you could readjust for the OD to come in at the speed you want.

Often the plating on the ground plate stops being conductive and prevents overdrive engagement. The Super 8 governors seemed to have been calibrated for earlier engagement. I assume it's the fly weights. The high torque Super 8 can engage overdrive much earlier than, say, a six and Packard was doing everything they could to compete with Hydramatic.

Anyway, try running a wire pigtail from the governor ground screw to the chassis. Or use an ohm meter to verify you have a good chassis ground to the governor contacts.

In general, the switch wasn't meant to be adjustable, which is why I chose to change the governor weights themselves.
Here's the post:
packardinfo.com/xoops/html/modules/newbb/viewtopic.php?post_id=58047