Engine vacuum ports/lines question

75LandYacht

Yank Tank
Joined
Oct 1, 2015
Messages
5,825
Reaction score
6,064
Location
Westchester NY
Good day fellas. Need your input regarding vacuum ports and lines on the engine. I’ve pulled the intake manifold on my 77 440 for some general upkeep cleaning and painting. on the back of the manifold is this vacuum tree, as you all know there are several devices under the hood that require a vacuum, brake booster, vacuum advance on the distributor, vapor canister for the fuel tank, HVAC / ATCll system and such.
My question is does it matter where these devices pull the vacuum from? This vacuum tree had a few lines to it as did the front and back of the base of the carburetor, And I want to reroute and clean up these vacuum lines when I put everything back together. So as long as I match the vacuum port size to the vacuum line requiring it doesn’t matter where they’re pulling the vacuum from?
Hope that wasn’t too confusing. LOL appreciate your input.

BE6D9A92-C6CC-43E1-963B-665F3E4C3BCC.jpeg


3EBA8A13-1A90-4129-B0B0-25AC68F6DDD6.jpeg
 

thethee

Well-Known Member
Joined
Feb 13, 2021
Messages
817
Reaction score
831
Location
Netherlands
Was typing something up but then I realised I might have misread. Do you mean if it matters what line you put on what "branch" of that tree? In that case I'd say no it doesn't matter
 

3175375

Senior Member
Joined
May 16, 2018
Messages
2,504
Reaction score
4,398
Location
Centerville, South Dakota
Good day fellas. Need your input regarding vacuum ports and lines on the engine. I’ve pulled the intake manifold on my 77 440 for some general upkeep cleaning and painting. on the back of the manifold is this vacuum tree, as you all know there are several devices under the hood that require a vacuum, brake booster, vacuum advance on the distributor, vapor canister for the fuel tank, HVAC / ATCll system and such.
My question is does it matter where these devices pull the vacuum from? This vacuum tree had a few lines to it as did the front and back of the base of the carburetor, And I want to reroute and clean up these vacuum lines when I put everything back together. So as long as I match the vacuum port size to the vacuum line requiring it doesn’t matter where they’re pulling the vacuum from?
Hope that wasn’t too confusing. LOL appreciate your input.

View attachment 546589

View attachment 546590
Doesn’t matter which port is used. However, if there’s a restrictor in any of those ports, then that restricted port would be for a specific purpose.

I doubt that any of the ports on that fitting are restricted, but I also am surprised that a 5 port fitting exists.
 

thethee

Well-Known Member
Joined
Feb 13, 2021
Messages
817
Reaction score
831
Location
Netherlands
I also am surprised that a 5 port fitting exists.
My '75 Imperial also has that.

Auto park brake release,
HVAC,
Speed servo,
and 2 for emissions control

Speed servo connects to the manifold as the booster nipple connects to the ride height leveler
 

CBODY67

Old Man with a Hat
Joined
Mar 27, 2011
Messages
7,777
Reaction score
4,877
There's a reason that one port location has so many take-offs from it. Even GM uses such multi-line vac trees, just that theirs are vertical rather than circular. The size of the individual take-offs matches the amount of vac that is needed for the particular item. Hence, the power brake line is the largest and it is in the center.

Some items will work directly off of the vac level at the port as others will use a modulating device to get the correct amount of vac to a particular location (think "Thermo Vacuum Switch"). While others will use a "vacuum bias" (as in the evap emissions system) to control things.

Thermo Vacuum Switches will modulate WHEN a particuilar device is activated with relation to engine coolant temp. Ensuring the engine is at "operating temp" before a device is activated, which can relate to the evap emissions system and EGR, both of which do not operate during the basic warm-up period. Just as there is a small thermostat in the base of the air cleaner to close the "trap door" in the snorkle so that warmer air from the exhaust manifold "heat stove" gets into the carb rather than cooler/cold air from the ambient air supply. As complex as these systems might be, individually, they are really quite simple. They also need to work together for best desired results and emissions compliance.

Typically, that rear intake manifold port where the fitting is installed is somewhat consistent amoung OEMs, it seems. In some cases, some carburetors have a screw-in fitting on the back of the carb base plate for the power brake booster, specifically.

I will agree that the engine compartments did look a bit cluttered with the many vac lines and such, BUT if you desire to "make it look better", then follow the vac hose routing (decal under the hood and in the FSM, possibly) to make sure the hoses got to where they are intended from that ONE main vac tap. You can use more hose to loom the hoses together, for example, rather than having them route on the shortest route to their destination, for example.

I strongly recommend that you get a copy of the particular FSM to study BEFORE you start your beautification project. That way, you can study what is in the FSM and start to plot your course in your project. Then, use some bare welding rod to bend to use to measure the amount of hose needed in which particular diameter.

DO get quaity hose!!! They all might look the same, but can vary as to thickness and type of rubber. You do NOT want a vac hose that will collapse because of the vacuum in it!!! Indicate to the auto supply counterperson that you want ONLY OEM-spec vac lines and why. You can use reinforced rubber fuel line hose for the power brake booster.

There are also some other hoses under that hood that might could use some looming, too. Of course . . . pictures when done?

Enjoy,
CBODY67
 

75LandYacht

Yank Tank
Joined
Oct 1, 2015
Messages
5,825
Reaction score
6,064
Location
Westchester NY
Thank you All for your input.. putting everything back together will go more smoothly because of your help. Thanks again
 
Top