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Maybelle is my newest/oldest 1950 Packard and the only one fully "manual iized" with steering, brakes and the R11 overdrive. My biggest question, now that we are having some warm January weather, occurred when I first started driving her on long stretches of smooth roads at speeds approaching fifty MPH. The overdrive knob is fully pushed in, but I cannot feel or hear much difference in engine speed when I lift my right foot at speeds above 25 mph. All seems smooth and there's definitely no clunk if it is going to overdrive, and nothing seems different when speeds drop below the magic 23 mph. With the warm weather, the windows are down, so wind noise may be also fooling me. Are these units really this transparent in their operation or is mine just not working correctly? Having a tachometer would solve this mystery, but I am still only guessing that everything is working well.

My bias tubeless whitewall tires are looking good but are also of questionable age, so there's no real highway speeds envisioned for the present. But still, I don't see any future of effortless cruising at 70-80 mph speeds, even if the OD is working well. I will just be satisfied for no drama at speeds hovering around fifty to remind me of the road conditions Maybelle faced 67 years ago.

My wife wondered if even Rosie the Riverter would have found a new Packard in 1950 easy to drive with her biceps and required planning ahead for stops and curves. She's sworn off driving Maybelle and the 1967 Corvette with a similar lack of powered technology. Perhaps women of that era were just in much better shape.

One very basic way to determine of OD has engaged is to get up to some speed of 35 mph or more and just take your foot off the gas. If engine compression is slowing you down (that is, the engine is still rotating at road speed), then your OD is not engaged. If it is engaged you will "free wheel" when you take your foot off the accelerator, i.e. no engine compression effect slowing you down.

If after doing the checks O_D suggested the OD still does not appear to be functional check a few spots on the electrical side. All are done with the engine off, car sitting, and OD knob pushed in.

In step 1 you should have 6v to ground on both sides of the fuse at all times. Sometimes the fuse holders oxidize and cannot carry the current needed for the solenoid..

Step 2: turn on the ign switch and with OD knob in you should have voltage at the relay ign terminal. If no voltage, the lockout switch has been a known failure item due to wear on the switch plunger.

Step 3: If you have voltage at both places, check the relay by momentarily connecting a jumper wire from the indicated terminal to ground. The relay should click and the solenoid should clunk and try to come in. If the relay clicks it is OK. It may be hard to hear the solenoid over the relay so if you do not hear the solenoid, remove the temporary jumper from ground and connect the meter to the relay out contact. Touch the jumper again to ground and when relay clicks verify there is voltage at the relay out contact. If there is voltage, providing the wiring is good, the solenoid should be getting power. If no voltage out, the relay contacts are known to oxidize.

If everything electrical checks out at the relay and still no OD then there could be governor, kickdown switch, or wiring problems preventing the relay from getting a signal to energize. If relay is energizing but no solenoid, wiring or the solenoid could be at fault...There is a set of contacts inside the solenoid that needs periodic servicing or solenoid could be burned out .

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Here's a video demonstrating how the overdrive works on a 48. Sounds like it could use a tune up.
https://www.youtube.com/watch?v=hVFiRkkvask
Wes