Packard Forum Index » Post-War (1946-54)

It looks like the wire to the distributor is missing. If I read correctly, that wire is the "interruptor" wire that momentarily stops current to the engine to drop the unit out of overdrive. Would a 14 GA wire work?

14 ga wire is fine. The wire should be connected to the same coil terminal as the wire that is going down to the distributor but a connection at the distributor terminal will also work.

The missing wire is actually a ground that starts at the solenoid. When solenoid plunger extends to engage OD an internal contact in the solenoid closes which puts ground on the wire. That ground goes up to the kickdown switch and connects to one of the top terminals. Those terminals are normally open so ground goes no farther.

When kickdown is desired, the quick accelerator movement to floorboard pushes the kickdown switch plunger and opens the bottom contacts in the switch so relay can drop out and cut power to the solenoid. Slightly after the bottom contacts open, the top contacts close to pass the ground on to the coil. The ground at the coil shorts out the points so spark stops being produced. The no spark condition causes the engine to miss and that relaxes the torque in the OD so spring in solenoid can retract the plunger and drop the unit out of OD. As soon as the solenoid plunger is released it starts to move back and the internal contacts supplying the ground to the coil wire open again. Ground goes away and coil can start producing a spark so engine resumes firing. The entire sequence is timed to last only a few milliseconds. There is not an exact time given for the sequence to occur and documentation says only that the action results in a "few" missed sparks.

No idea why someone would disconnect and remove the wire and switch but if the wire to the solenoid contact is shorted under the car or something is broken in the solenoid or something mechanical in the OD keeps the solenoid plunger from retracting quickly, the ground could remain present long enough to kill the engine. Keep that in mind if you have a problem after connecting things back up.

Here is a good 51-4 diagram that shows all the contacts.

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Very good and detailed explanation! In todays automotive world it would take a computer to figure all of this out in a split second. It just amazes me that they came up with such a detailed but basically simple method 70+ years ago as I'm sure they used something similar in the previous overdrives as well.

Thanks again Howard.

I noticed that this car has a negative ground. Will that affect the kickdown and fuel gage?

Nothing on a stock Packard except maybe some of the voltage regulators is polarity sensitive. Some regulators are designated positive or negative ground but so far no one has provided any official documentation as to why or what there might be as a difference. Speculation has it because of coating or composition of the regulator contact points being different to lessen arcs when the contacts open and close but no proof of that. The generators are repolarized when battery polarity is swapped and even those regulators that are designated seem to function and keep charging properly although it could be their life is shortened.

If the car has had any modern conversions that use solid state components such as the old style radio vibrator replaced or a modern instrument voltage regulator or more commonly, LED light bulbs installed then there could be issues with those items.

I had often wondered if changing to 12v what effect that would have on the voltage regulator that drops voltage to 5volt for the dash instruments??

An interesting question. Logic would say it would burn out yet the 54 6v regulator has the same part number as the 12v item used in 55-6. There have been any number of 51-3 models which have a different part number regulator that have been converted to 12v. I don't recall anyone mentioning a problem after the conversions.

The regulator uses a heater to bend a bimetal strip to open and close a contact. That action provides brief pulses of full battery voltage to the gauges. The regulated voltage value is calculated between the on and off times to be the average value of 5v the 51-6 gauges use. It could be the action is more rapid at 12v so the regulator heater or gauge heaters never see a long enough on time of 12v to get damaged.

Prior to 51, instrument regulators were not used so those earlier cars definitely need something to lower voltage to the gauges. The Runtz solid state device is one option but seem to be sold for negative ground only. Resistors are the fall back and probably the most common solution.

Here is the regulator internals and an oscilloscope view of the action from a 54-56 regulator at 12.6v. In this example on time is just over 100ms and off time just under 500ms. Don't remember if I had 2 or 3 gauges in the circuit when taking the reading but the gauge load would vary the timing of the pulses.

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I actually have a kit from ebay for a 12v conversion. I hadn't done it yet on my 52. The 51 has an electric fuel pump that would have to be changed. Also would that have any effect on the overdrive unit?

The stock OD will definitely be damaged on 12v. Switches would not care but the relay and solenoid would need to change or else have some kind of independent power to keep them at 6v. Resistors will not work in this case because of the varying load of the solenoid when pulling in vs holding in position. A separate battery or a 12v to 6v converter rated for the heavy pull in current would be required. The OD unit is fused at 30 amp and probably pulls an easy 20 when solenoid is engaging. Those type converter units are typically spec'd as rated for motor use. Ordinary converters rated for electronics only use would not have the needed protection for the heavy start current or back inductive voltage spike a coil emits when power is disconnected.

Fortunately the R11 relay and solenoid have been repro'd and are available for both 6 or 12v operation. While somewhat expensive, the repros are easily found. Those with an R9 OD have no repro items so are out of luck and will need to provide the proper voltage to the unit.

More trouble than it's worth! I may try it on my 52 if I decide to keep it and rebuild it. The only thing that makes rebuilding the 52 questionable is the windshield. The only one I was able to find is at Merritt's and they want $1250 + shipping. I just can't do that.