I'd take a good look at the compensator valve because your symptoms describe what happens if it doesn't seal tight immediately when pedal pushed-- a known issue with details on another thread in the forum. There might be a slim possibility the rear hose failed and dumped the fluid where you made the panic stop but you'd have known that immediately with the lack of a next stop. If the reservoir is full and no signs of leakage anywhere else, that valve is about all that's left.

Just curious about how you are trying to activate switch. You mention 40 & 70 lbs. One of the power brake sites mentions drums need 750 lbs minimum to stop, discs 1500 and list specs on their various units all the way to 2500 lbs so 70 might not be quite enough to do anything.

The original switch had one circuit with the common lead and normally closed going to TL and normally open to the brakes. When pressure applied the contacts reversed. The mechanical has 2 separate switches thus the need for pink wire to both ends. Since it is mounted with button pressed it is now "actuated" in normal operation so the logic is reversed with the normally closed to brakes and normally open to TL.

Your logic is correct. This is a common failure with the switch--particularly if it's been around silicone fluid. NOS available but pricy. There's a VW replacement some have had luck with (113945515G) that has different terminals--blade vs the round bullet type--so if you have blades, perhaps someone has already switched.

Another option is to convert to full mechanical operated by brake pedal. The picture shows one method of mounting and the parts I used. Mr. Berger sourced the Standard aftermarket switch at his local parts store.

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Without some real troubleshooting, it's going to be difficult to narrow down to electrical or mechanical. Mechanically, the only thing I can think of without a teardown would be make sure the lockout lever is adjusted properly and fully engaging or disengaging with the lockout knob moving the lever down on OD full travel. Electrically if kickdown sw OK, that leaves governor as next most likely & relay or lockout sw down the list.

Packard did issue a service bulletin after the war on that same series OD where a problem had been found with the connectors that joined the harnesses corroding and causing problems. Don't remember if all years were mentioned but if you have a harness that has the bakelite connectors (5 or 6 of them)about 3-4 ft from transmission then possibly that is causing an intermittent problem. I don't see how it would be load related unless there is a poor connection which heats and fails or jiggles open about the time you get to speed.

Can't tell you where they came from but in the past I've bought sets for various years from Terrill Machine. The engine rebuilder didn't squawk when I gave them to him like he did for some items so they must have been decent. No longer own the cars but at least 2 are still in area and as far as I know, no problems.

Welcome also. Regarding the overdrive, have you been able to determine if it is electrically disengaging as if the kickdown switch is misadjusted and coming in early or if it's mechanically failing. There is an overdrive manual here in the Articles--Service Manuals and Wire diagrams (item 31) section you can read or download which might be of some help.

Cast iron, actually integral to and forms crankcase bottom of Leheigh compressor. In the picture "top", the idler pulley is shown 180 reversed.

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There are several threads on the AAC Packard forum on the subject.

http://forums.aaca.org

Doing a search for "Chrysler" after you're in the Packard forum brings up one but there are others. Can't give the exact words to search to bring them up. Some have had luck, other not so thrilled due to various reasons.

Another alternative might be the GM transmission here:

http://www.mikestransmissions.com/Classics/UltraOD.html

and I believe there is a TH400 conversion also available from another vendor.

My 2 cents say go for it. Personally, I'm partial to the 57 because to me it was very well done and a nice car under the circumstances it came into being while the 58's were just a bit too much and kinda broke the continuity. You're right that some might raise an eyebrow but so what-it says Packard on it. Very sorry now that I didn't buy a 57 P. a few years ago when the opportunity came by. Am sure you'll be welcome--