Vacuum Advance Leak Down

[Omni]

Good Morning All
Still doing some tweaking on Party Barge. In checking the vacuum advance unit it is full open @15"hg but will bleed off to '0' in less than a minute.
Is this normal or has the 58 year old diaphragm gave up? If it is bad, would I replace it with another 15"hg or should I be looking for something more compatible with todays' demands?

Thanks to all who respond
Omni

 

[3175375]

Doesn’t sound normal.

 

[CBODY67]

Not normal. Maybe a little amount of movement in that time, but not a complete leak-down.

The length of the travel of the plunger determines how much advance the unit has. Matching that travel would be best.

I suspect at this time, that all vac advance units are similar and adjustable. Slide an Allen wrench the size of the ID of the vac hose attachment into the hole. If it will index with an adjustment on the diaphram, you can vary the spring pressure and when the advance maxs-out. Might not need to do anything, either.

As I understand it, a Chrysler electronic dist vac advance is not the same as a points ignition vac advance, fwiw.

Key things are that the new item holds vac better and the plunger moves a similar amount.

Enjoy!
CBODY67

 

[70bigblockdodge]

Should not bleed off ideally. Most of the time if they are truly bad they will not even pull a vacuum (you can just suck air though them) so yours is not "shot", but I would start looking into a new one. Points ones are hard to find. Tony's parts had them repopped and he is proud $$$$ of them. @halifaxhops had a few he happened across recently. That could be your fuel mileage problem if it is lazy to operate, not getting to full vacuum advance promptly. I have redrilled my plate under the points to use a electronic dist. "inside arm vacuum advance which are readily available.
Beware! I have bought vacuum advance canisters on rock auto that list as 196x, which would be points and a small block canister has shown up on my doorstep. Small block has arm outward , but they rotate clockwise so they will not fit a big block distributor.

 

[Omni]

Thanks to both of you for the responses. I had forgotten about some replacements being adjustable.
Turns out I had one (adjustable) that carries good vacuum. As a bonus I was able to replace it without removing the distributor.
Thanks again
Omni