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If you try rebuilding the Treadle-Vac yourself, Cadillac Parts Unlimited offers the complete kit and they do have the vent hole in the top cover gasket. The kit is missing the dust seal behind the pedal but has everything else and if you really need the dust seal, I have them available on my site.

Thanks so much PackardDon! Will look at all that. I spoke to a parts supplier near here and he told me some poor fellow paid over $2000 (cdn) to have his TV unit rebuilt locally.........yikes!

so I have the original 3 pole brake switch, the dark green wire is spliced to a yellow wire that leads to a switch and then the fuse block.

I found a post where a 2 prong switch can be used and a relay. that should be the way I should go now perhaps?

as a side note the white wire with the alligator clip goes to the light switch I think, I haven't quite figured out what that is about yet. have to be a contortionist to see up there....that I am not.

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Personally I don't care much for those Rube Goldberg contraptions but the original switches are no longer available. Even if you found one NOS, it may not handle modern brake fluid (I prefer synthetic) but there is a VW switch that is virtually identical except that it has flat blade connectors rather than the round ones. Finding one of a known quality brand of modern construction, it should be able to handle it and would be easy to make an adapter.

It is really hard to say what someone might have done with the TL wiring. Probably not having a complete schematic has made many do a Rube Goldberg thinking they will solve a malfunction or work around a faulty switch. Here is the complete 56 diagram showing all contacts in the black boxes just in case you missed downloading one posted in other threads.

This diagram also shows the optional 56 manual switch as Packard designed it to add into the existing wiring without bypassing the limit switches and to automatically disconnect the power to the automatic level control box to disable it when manual is used. Without the optional manual switch in the circuit the light green wire is continuous from the brake switch to the under dash on/off switch and the extra two wires in a separate loom to the control box are not present.

The VW 3 terminal switch is an option but there have been some that report issues with those having a short life also. One advantage of the 2 terminal switch and relay approach is the 2 terminal switches are inexpensive and can be found at almost any parts store. Even if those have a short life too it is approx $15 or less to replace from the corner store instead of trying to find a specific and more expensive 3 terminal. You can buy premade kits which just plug in from some of our vendors and regions or you can make your own with a switch and inexpensive relay and socket.

Another approach some have used to eliminate hydraulic switch issues completely when using silicon fluid is replace the hydraulic switch with a mechanical switch operated by the pedal arm.

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That's a lot help gentlemen, thank you!
I will have to start writing down where I see items of help/interest , or just copy it. With so much information on this site it's easy to go in circles

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Howard, that is actually the Rube Goldberg approach that I was taking about. It works around the problem by employing a different method to do it but it does not actually fix the problem itself. Rather, it ignores it.

I can sympathize why the person who did your changes tried to come up with a workaround. The original 3 terminal brake switches were somewhat hard to find after Stude went away and even more so after the 70s when it seems like the mention of buying any low production orphan car part was a bad word -- basically until the days of online search and internet vendors came along. The switches were expensive then and even more so now that supply of originals is all but extinct so it is understandable why some kludgy attempts to replace them were made.

Honestly, until Packardinfo came along service literature and wiring diagrams were not plentiful to even know how the TL system worked. There were a few offering hard copy reprints of various quality of the more general literature items but unless you were a member of a club even that availability was not well known. Packard parts in general were harder to find because auto parts stores never carried that many Packard aftermarket items anyway and there were only a few vendors selling the NOS parts they had the foresight to buy up from defunct dealers. It was word of mouth thru clubs or an occasional ad seen in an old car auto publication to even know where to look for those people.

I don't know who came up with the first cross to the VW switch. I first heard thru the Packards International Club that there was a switch made by Wells that many used (maybe that was the VW cross) but then reports came along that those turned out to be problematic for some reason and there were many negative comments about using them -- maybe due to the silicon fluid which was being heavily promoted by some clubs in those days for use in cars that did a lot of sitting. The mechanical switch conversion was an effort to both eliminate silicon problems and the difficulty in finding a 3 terminal switch. That might have come from PI also because in the 70 and 80s they were a very active club in coming up with mods to keep Packards on the road. No idea who came up with the 2 terminal and relay conversion either but I think those are relatively recent with promotion and availability of the kits only starting a few years ago.

My father was a turbine mechanic back when, so I expect it was his work around to keep things working. Have found numerous of his letters to Packard International asking for wiring diagrams and the like, copying costs were prohibitive for a lot of information it would seem in the 60's. As I am not restoring a show car, but a driver the 2 mechanical solutions seems reasonable.
Thanks for your input and interest

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Very true. The commercial Xerox machines were still fairly new, rather large, and terribly expensive so not many businesses could afford one. No computers or printers then and the ordinary home or small office copier was non existent so small jobs were cumbersome at best. Carbon paper was the norm for the occasional copy in small offices and mimeograph or stencil printing for larger needs.

I remember there was the photostat copy method where you had to shine a light thru the original and onto a special paper. That was OK if the original had single side printing but as I recall depending on the quality of the original and the paper it was written on, the copy might not be that great. After the exposure you placed the copy paper in various drawers in the photostat machine for developing with heat and chemicals. It was time consuming and took training to make a decent copy. No idea what you did if you needed to copy a double sided original -- maybe to a photo shop for a camera to photograph and print out a photo. All said, there were no corner copy stores where you could just walk in and get a quick copy -- at least not in smaller cities -- so it is understandable that PI might have wanted a few bucks to copy some diagrams.