Vacuum Canister

[bucks77ford]

I need to look at a vacuum line diagram for my 75 supercab, but just a quick question. When my 460 requires more vacuum, I lose the vacuum supplied to my A/C-Heater controls and the air goes from vents to defrost. I'm assuming I need a bigger vacuum canister. I do have one vac line that goes to nowhere and another on the drivers fender that goes to a small vac canister. My 77 has a large canister mounted on under the drivers inner fender and I don't lose vacuum on it. I'm just wondering that since I have a vac line that isn't hooked to anything (except just having it plugged) can I run it to a larger vac canister to provide a more reserve?

 

[dustybumpers]

On the newer trucks(gen 8-9) that is a bad vacuum line to the door actuator under the hood. I assume the controls for the early model system are similar.

The line that goes bad is the white one that comes from the heater control, to the actuator under the hood. It is in the wiring harness that also includes the black nylon line that feeds the heater control. Usually the cause of the problem is heat from the passenger side exhaust manifold makes the nylon line brittle, and it gets riddled with cracks.

 

[fatherdoug]

On the '78 the large vacuum canister on the driver's fender is for the cruise control. I also have a smaller reservoir just in front of the ignition control module, that is about half the size of the other one. I have also seen a larger one mounted on the battery tray.

Might also want to check the integrity of the vacuum selector valve behind the heater control panel. I am only familiar with the '78, and am ASSUMING the 75 would be similar.

 

[m78]

I need to look at a vacuum line diagram for my 75 supercab, but just a quick question. When my 460 requires more vacuum, I lose the vacuum supplied to my A/C-Heater controls and the air goes from vents to defrost. I'm assuming I need a bigger vacuum canister. I do have one vac line that goes to nowhere and another on the drivers fender that goes to a small vac canister. My 77 has a large canister mounted on under the drivers inner fender and I don't lose vacuum on it. I'm just wondering that since I have a vac line that isn't hooked to anything (except just having it plugged) can I run it to a larger vac canister to provide a more reserve?

I would say yes to adding the extra cannister. Also , a larger tubing size between that cannister and what it is supplying vacuum to would help supply the vacuum to it.

 

[Fellro]

More what you need is a check valve to keep from losing the vacuum you have. Your truck doesn't "need" more vacuum, when you stomp on it, you actually have less of it. A larger or additional canister will not help when all of it drops... You need is a means to keep what you have in the reservoir from going back towards the motor. That is where the newer models use a check valve. The actuator is a steady pull, so it doesn't need additional vacuum pull, just steady.

 

[m78]

^ Good point.
On another note, it might work fine down here at sea level.

 

[Fellro]

I'm only 400' above sea level...

 

[5.0Flareside]

Yeah when you go wide open you pull 0" of vacuum..

There should be a check valve to hold vacuum in the hvac system to make controls continue to work..


Sent from my iPhone 4 using Ford Power

 

[bucks77ford]

Thanks for the replys. I'll have to put in a check valve. Since I have a vac line that isn't connected to anything and one that is already connected to a small cannister, I will ad a larger one and a check valve. The heater/ac controls work fine until I am using more power like pulling my camper or WOT.