Flathead vacuum line 21A-12226

hb32

hb32

Well-known member
It appears that I am missing this line and am trying to figure out what I can do to make one. My pickup is far from original so oem is not a concern but running properly is. The intake manifold is an original Edelbrock regular which the previous owner drilled but did not thread, 2 holes, near the mounting bolts into the runners. From research, the line has a banjo fitting on one end and nothing on the other. It seems that the bolt that threads into the manifold is made of unobtanium as well.
What diameter is this tubing?
What threads into the timing cover?
My intent was to utilize both holes with the second for vacuum wipers. Knowing the diameter would allow me to determine a thread size for a Weatherhead style fitting.
Thanks for the replies.
 
The vacuum line to the distributer is designed to operate the "snubber" piston to retard the timing if you have spark knock under heavy pulling. With today's fuels, it usually isn't necessary. When we rebuild a distributor we back off the adjustment all the way, anyway. It is a good idea to plug the port on the distributor so junk can't get in. Go ahead and use the available port for you wipers.
 
42 to 48 had a special banjo bolt set up to connect to the intake manifold below the carb base. The other end has a small brass compression fitting to connect to the distributor. It's about the same fitting that was used on Ford distributors up into the 60s. A lot of the later post war cars had a banjo bolt with a chamber in it to quiet the pulses for vacuum to the wiper motor. They were either made from aluminum or pot metal. The earlier types used a line from the left side of the intake manifold to the vacuum brake and both ends had the little brass compression fitting. I think is is part number 91A-17542 for those but I think there was one for a smaller line and one for a larger line and I don't know which is which. I think the later number is 351112-S for the compression fitting. They look about the same but one is an earlier part number. These may have been superseded by later replacement part.
 
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To answer your original question; the dia of the line is 3/16. The fitting into the timing cover is called a dole nut.
 
Thanks Brian. I suspect the timing cover side uses a compression style fitting with a ferrel?
 
The manifold did too on the earlier Fords. P/N 11A-12226 was the line with compression fittings on both ends. A person would have to use a Weatherhead or other fittings on a manifold that has no machining for the early type fitting. This would require use of tapered pipe attachments but that type stuff it out there if that's the way a person wants to go. I think Ford moved the fitting to the carb base area to get a more uniform vacuum sample. Taking it off a specific intake runner might have a tendency to detune that runners flow a bit over the others.

The Ford 3/8" compression fitting pinched onto the line the farther it was tightened down into the tapered bore. You can look at the timing cover port and see how it's shaped.

Folks seem to think that the distributor doesn't need that vacuum connection. This is what releases the brake to get full advance. If it's not connected it will try to brake all the time. If you do away with the vacuum brake then the vacuum piston should be removed & lines plugged. I don't think I would mess with that. At least it has some retard when you get on it. It will get better mileage with it than it will without it.
 
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WOW what a discussion !!

I feel as if the vacuum piston and spring should always be ran with vacuum to it if possible. Without this load on the advance ring the spark will jump around at idle and be very unstable on the low end.
Properely adjusted with vac it will enable the engine to start slightly retarded just the way Ford designed it!

I install in all rebuilds and adjust to have a slight drag on the advance ring.

Just another opinion i guess..........:eek:
 
Thanks for the comments to date and feel that the vacuum advance is necessary as well so will be utilizing it. I am trying to source an original line which will allow me to utilize the special nut that threads into the timing cover and fab something for the opposite end.
 
BUBBAS IGNITION said:
WOW what a discussion !!

I feel as if the vacuum piston and spring should always be ran with vacuum to it if possible. Without this load on the advance ring the spark will jump around at idle and be very unstable on the low end.
Properely adjusted with vac it will enable the engine to start slightly retarded just the way Ford designed it!

I install in all rebuilds and adjust to have a slight drag on the advance ring.

Just another opinion i guess..........:eek:
Click to expand...

Jim, since manifold vacuum is what pulls the piston away from the advance ring, and vacuum is highest at idle, isn't it normal for there to no load on the ring at idle?
 
In response to my previous reply, I use the vacuum brake plunger and spring and hook the line up, however I usually leave it adjusted all the way out. I bend the thin inner weight springs to insure the weights return back to static at idle. If not bending the spring I only use slight tension on the vacuum brake.

Keep in mind this is a vacuum brake NOT vacuum advance.
 
The old Ford system is not an advance, but a retard mechanism in the event of preignition under load. The advance is strictly due to the action of the distributor weights working against leaf springs on the distributor point plate. The vacuum plunger system does not affect the starting unless the distributor has not been assembled and adjusted properly. We test all distributors on our Sun machine to be sure the advance is within specs. The nose of the snubber is usually heavily grooved from wear, and doesn't work well, if at all.
 
The vacuum brake would have no vacuum acting on it till the engine starts. The vacuum build would be rapid so it would quickly be relieving any pressure on the advance rotor. RPM is what makes the flyweights react to centrifugal force. The springs allow full retard for starting and delay full advance as long as intended by the design pressure.

Vacuum advance was kind of a misnomer from the get go. Vacuum retard would be more accurate on all of the old points systems. A lot of manufacturers referred to it as vacuum spark control. Folks that didn't completely understand the systems came up with vacuum advance.
 
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40 Deluxe said:
Jim, since manifold vacuum is what pulls the piston away from the advance ring, and vacuum is highest at idle, isn't it normal for there to no load on the ring at idle?
Click to expand...

I guess i should have said pre-idle , engine off it holds the advance ring in a retarded position and does in fact pull off when the engine starts.
This improves the starting of the engine.
At the Ford convention two years ago i had a swap meet space next to the concourse and wish i could have recorded each and every engine on first start up..large variation for sure ....

I have heard it said that a flathead would start when it seen ya coming???
 
supereal said:
The old Ford system is not an advance, but a retard mechanism in the event of preignition under load. The advance is strictly due to the action of the distributor weights working against leaf springs on the distributor point plate. The vacuum plunger system does not affect the starting unless the distributor has not been assembled and adjusted properly. We test all distributors on our Sun machine to be sure the advance is within specs. The nose of the snubber is usually heavily grooved from wear, and doesn't work well, if at all.
Click to expand...

Engine off the vacuum piston is pushed in against the retard ring causing a slight retard when cranking . Once engine starts it pulls outward allowing full advance...:)
 
I think that's vacuum advance, isn't it? I've always heard "vacuum retard" in relation to these, but it never seemed right to me.
 
BUBBAS IGNITION said:
WOW what a discussion !!

I feel as if the vacuum piston and spring should always be ran with vacuum to it if possible. Without this load on the advance ring the spark will jump around at idle and be very unstable on the low end.
Properely adjusted with vac it will enable the engine to start slightly retarded just the way Ford designed it!

I install in all rebuilds and adjust to have a slight drag on the advance ring.

Just another opinion i guess..........:eek:
Click to expand...
Since the piston is pulled away from the breaker plate when running(except under low vacuum conditions), if you have irregular spark then you have wear in the distributor. Has nothing to do with the plunger.
 
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