I have a 360 motor, auto. This is on the back of the engine, passenger side, behind the carb. The smaller hose goes to brake booster, and the back 1/4 hose goes down and to the transmission. It was painted blue when the engine was rebuilt, I've been spraying carb cleaner to find a vacuum leak and the paint came off. It also looks like someone tried closing a port off with a screw because that just doesn't look right.

 

I would think the larger hose would/should go to the booster, and the smaller hose to the transmission modulator valve, if you have a C-6 automatic.

 

You're right, I had the description swapped. Do you know what that part is called?

 

Secondly, does it unscrew? I believe there is an air leak here.. which I'm hoping would fix my current situation.

 

I've never had one off, and it's been so many, many, years (well past 30) since I looked, I can't remember.

The screw is something I don't know is supposed to be there or not. Try plugging the small hose and see if that helps whatever problem you're having. Or, plug both off, but don't drive. You could have a bad modulator valve and have a vacuum leak, but you would probably be using transmission fluid and have white smock coming out the exhaust after coming off a hill then giving it gas. The brake booster could be bad sucking air also.

 

That piece is a vacuum tree. Most are threaded 3/8 NPT. Your vacuum leak could easily be a diaphragm failure in either the brake booster or the transmission modulator calve. Both are relatively easy to swap out. There are very inexpensive rubber caps that are made to close off unused vacuum ports. I would suggest getting some of those and temporarily capping all of the ports on that vacuum tree (including the one that you take the screw out of) See if capping all the ports off cures your vacuum leak. If it does - then see if the vacuum leak problem comes back when you add the brake booster hose back to the vacuum tree. If not - then add the modulator valve hose back back to the tree and see if the problem comes back.

 

Thanks for the feedback! I'll do these tests and see where it takes me. I never noticed the screw closing the port until now. Would a vacuum leak like this potentially cause the engine to fluctuate in rpm after it has warmed up? I'm running into a situation when my rpm are steady are start, then after the engine has been running for an hour they start to decline/drop.

 

Yes, that is a classic symptom of a vacuum leak.

 

Vacuum tree is the most common description, but that comes from the type that actually do look like a tree of sorts. with multiple branches off of a center stem.
This older type is probably best described as a "vacuum manifold" I would think. And yes, they almost always unscrew as was said.
The problem with your particular type is that the longer large tube/elbow thingy likely gets in the way of anything else bolted down. Might be hard to turn it in a full circle without clearing the manifold of things like the carburetor and other fittings.
Or it might come right off!

I always had an easy time with mine, but worked on other cars where it took half an hour to get one off because of all the other junk that had to be removed around it. Not fun at all.

The screw was probably used because there wasn't an actual tube fitting coming out to put a cap on.
And speaking of caps.... Buy only good ones! More expensive, or maybe silicone caps? Or some good material. The cheap modern imported rubber versions just rot out within months and create more leaks.
In fact, instead of caps many of us still revert to our childhood training and use hose with a screw or bolt! Because the fuel rated hose lasts years longer than the rubber caps.

As said though, cap them all off and run the engine up to temp and see if spraying some liquid around the fitting changes the idle character. If it does, it's leaking.

Paul

 

In Ford's "Standard and Utility Parts Catalog" dated 2/2004, there are two vacuum manifolds that might work. However, both were discontinued prior to this catalog's printing. I don't see any out there N.O.S.
You have two choices. First, remove your old one and thread the hole with the screw in it correctly then plug it. Second, go to a local parts store and buy something that will work. Maybe down their "help" isle. It may have all hose nipples and too many of them. But you could also delete the threaded in tube mounted to the side of yours.

 

Do you still have the stock air cleaner? I think the blocked port was used to run the air door on the stock air cleaner assembly.

As said above, pull the vacuum manifold and clean that up by taking out the screw and either thread it for a proper plug, or solder it shut.