The Stovebolt Site Forums The Shop Area Driveline Vacuum line recommendations for Power Brake Booster

I’m in the process of installing a frame mounted Power Brake Booster/MC assembly in my ‘52 3100 and the instructions on CPP website say to install a loop in the vacuum line coming from the manifold due to the booster being below the manifold. It doesn’t specify if the loop goed up above the manifold or down.

Another search on the internet showed that a charcoal filter is recommended so gas fumes don’t deteriorate the rubber in the booster. I suppose the filter takes the place of the loop.

Can any you you ‘bolters give me any insight and resolutions to the issue?

This info is interesting as my instructions never mentioned the loop or charcoal canister. Maybe this is new technology! My conversion was several years ago.

All I have is a check valve on the booster.

C3 Corvettes had a filter on the vacuum line that went to to headlight actuators, but I have never seen one on the brake booster.

Maybe call and ask them?

The info was not in the instructions I received with the kit but from a QR code on a card that came with the kit for more installation instructions. I’ve included a link in my first post.

Some comparison from a big bolt: The Hydrovac booster is mounted on the frame below the level of the engine, mine is under the driver's side step. The vacuum line starts at the intake manifold and goes up to a combination inverted trap and check valve, it then heads down the firewall and along the frame to the booster. The theory for the loop/trap is to prevent gasoline vapor from condensing and running into the booster.

I put front disc brakes on my AD years ago and engineered it to use a firewall mounted MC/vacuum/power booster. Initially I did supply vacuum to it but the brakes were wayyyyy too sensitive. I had the thought to try it without the vacuum assist and was somewhat surprised to find that the brakes felt/behaved just fine without vacuum….just takes a little more muscle. I left the booster in place…with no vacuum connection. Been driving it that way for about 10 years. (“Real men” don’t need power brakes….or automatic transmissions….or fuel injection…or air conditioning, or etc etc….I’m joking….)
Phak1, try it without the vacuum?
Regards, Dave

I understand the theory about the gas trap. What doesn’t make sense to me is the booster has a check valve which holds vacuum in the booster until the vacuum drops below minimum then open to increase the vacuum in the booster. If the valve is shut closed, how would gas fumes reach the booster.

What makes any sense to me, is it’s there as a failsafe if the check valve fails.


By invert loop, do you mean like an inverted ‘U’?

Yes, inverted trap is like an upside down "U" or "P". In my application, the rubber vacuum hose runs from the base of the carburetor up to some 1/2" steel tubing, the tube is vertical and connects to the bottom of the check valve, then out of the top of the valve it makes a short vertical run and then a 180 degree turn and down to the frame.