Brake Booster Vac Line--Size? 70 Deville

[Jeff Rosansky CLC #28373]

Hello,
What size is the main vac line to the power brake booster?
I have replaced just about all the vac lines under the hood of our 70.  I think they added up to be longer than the car itself.  I want to replace the line for the brake booster but I can't find the size.  The guy at the part store couldn't find the size in his book either.  I was just going to bring in a piece of the old one in but someone had replaced it with 3/8 fuel line.  So, does anyone know what size the line is?
Jeff

[TJ Hopland]

3/8 seems correct.     I remember replacing them before and ended up using fuel line, same with the PCV line.   I don't know what the original stuff was but I don't remember being able to find 3/8 'vacuum' line. 

[Scot Minesinger]

First, excellent-you should replace all the under hood vacuum lines.  This seems to be one of the most commonly ignored crucial, inexpensive and easy repair items on these 1960's and 1970's Cadillacs. 

If the fuel line is the correct size, I would use that size again.  For some reason those fuel lines don't make as good of vacuum lines as vacuum lines.  If you can replace it with a true vacuum line, it will be less money anyway (fuel lines have cords inside the rubber for reinforcement) and it is for the best. 

In the fall we replaced all the vacuum lines on our recently acquired 1970 Cadillac and it made a very nice improvement.  The engine ran better and idled smoother.

Enjoy your 1970 Cadillac!

[Jeff Rosansky CLC #28373]

OK, I'll use the fuel line.  I've replaced all the underhood stuff other than the ones going to the hvac power servo and inside the car....... Not that I don't want to, I just ran out of line so I will need more.  It idles a little better but still vibrates a bit.  More projects for me to do, I guess.
Jeff