[Matt-G]

Just got my '62 Falcon drivable for the first time after a year working on it! It has a '68 C4 and 200 ci straight 6. I had some slipping issues with the automatic transmission so I double checked fluid levels and swapped out the vacuum modulator. While doing that I noticed whoever had this car before me used a length of metal brake line tubing as the vacuum hard-line from the manifold to the modulator. My gut feeling is the internal diameter of this tubing isn't big enough and should be replaced with the correct tubing. It was shifting pretty good but I didn't get to fully test it before my brand new radiator sprung a leak! Looking for advice on if that tubing should be charged. Thanks!

 

[Dominick 1]

As long as the vacuum tube is the same size as the modulator you should be good to go

 

[Action]

The diameter may not make that much difference. Leaks are more of a concern. The modulator (based on a vacuum signal) will cause the transmission to upshift. That is it.
If the transmission is delayed in upshifting then I would be concerned.

Action

 

[Matt-G]

Ok, thank you both! I'll leave it be for now and test more after I fix the radiator.