The Stovebolt Site Forums The Shop Area The Electrical Bay Old Horn

I’ve jumped on the horn bandwagon, trying to toot my own horn, so to speak.

This piece was given to me by a good friend, now deceased. It sure would be nice to salvage it, maybe use it in my ‘54.

There is a set of points that look adjustable. When I apply current the unit hums , as though it is stuck. Anyone know how to free it up?

I cleaned the points , no change.
The disk at 12 o clock gets hot real quick, if that’s any clue.

I have a junkyard horn that looks slightly better on the inside than yours. I bought it on ebay just to get the bent bracket to mount the other "good" horn on the exhaust manifold.

I have the same interest as you, now. From the outside, it looks like it spent 50 years at the bottom of a lake.

That contact at 12 o'clock has enough rust around it that it may contacting the ground around the insulating disk. That would make it heat up, and also divert some of the voltage from the coil so it won't move the diaphragm. You might try a soak in Evaporust to get rid of the rust. Evaporust shouldn't hurt any of the other parts, and it can't hurt to try. It's' also possible that the armature is stuck inside the coil. Maybe a little percussive maintenance will free that up, as well as the rust removal with Evaporust.

You referenced armature may be stuck in the coil - could you expand on that , help me understand how the horn is supposed to function?

I understand the internal combustion engine with its pistons, crankshaft, camshaft and valves ; I should be able to understand the horn with a bit of a nudge.

I.E. : what are those points supposed to do?

When you push the button, it engergized the coil and moves the pin in the center, opening the contacts and flexing the diaphram one direction.

When the points open, the coil de-energizes and the diaphram flexes back the other direction, closing the points.

By adjusting the preload on the points, you can change how far it has to move before they open, affecting the tone of the horn.

The armature is inside the coil and is what moves the diaphragm and the contact points. Fibonachu explained how it works. It's basically a solenoid system that gets turned on and off by the contact points.

The "on and off" of the solenoid is very rapid, that is what causes the vibration or what we perceive as the horn blowing it trumpet sound. I agree with the other members, clean it of rust, confirm that the armature is free to move, it should get better with GENTILE cleaning. You are in a better situation than I, mine won't hum, no heating of coil, I have continuity but don't know why it won't buzz.

So I should clean in every possible, and I can continue to try various point adjustments, but my problem seems to be centered around the lack of movement of the armature. I did a Kroil soak of those parts overnight; I’ll try the horn aha after church.

Noting that the horn works along the lines of a solenoid is very helpful. It makes sense. Thanks for “pointing” that out.
- Yes, that was another shameless pun. I’m tooting my own horn again, but not the one that counts.

I think I’ve reached the end of the road in my effort to salvage the old horn. I was able to separate the structure by drilling out rivets. With the diaphragm removed I could see that the armature was not seized, it moved freely.
I did observe 2 malfunctions:
- The opening of the points did not drop the electromagnetic field. The hum I was hearing was caused by the magnetic plates failing to separate, drawn together even though the points were open , field hot and parts getting hot.
- Even if the field had been cycling as intended, the magnet strength is insufficient to allow the armature to overcome the tension of the phenolic plate that one side of the points is mounted on. The only way I could get the plates & armature to move was to back the tension way off.

The internal fasteners and tension screw head were marred up indicating that someone had already attempted to repair the horn. Somewhere there must be a short because the points are inoperative. Lots of corrosion.

I gave it a good try , l now know how an electric horn is supposed to work, but I think this one is kaput.

Thanks for trying, guys.

Yeah, a short in the coil might be the cause of that one being T.U. With that much corrosion inside, it wouldn't be surprising.

I tried restoring several old horns that would only Humm when using a battery charger to power them. Changed to going direct to a 12 volt battery and every one I have tried to restore since has been a success. They need lots of amperage to make them go. Dave

You know, the one thing I didn’t try was the top setting on the charger, don’t remember how many amps that is.
Worth a try, nothing to lose.

Waveski. Most battery chargers are just that, battery chargers. They are not a power supply unit. Their circuitry must read a salvageable battery before they will put out the advertised amperage. Best to use a good car battery for testing a horn.

So happens I have a spare battery in the shop.
I will verify the condition of it and try that power supply.

Just hook a couple jumper cables to the battery in your daily driver and touch the horn contacts.

Well the battery did make a difference, but still no joy.
The increased amperage resulted in spurts of cycling of the points - and lots of smoke. I do not see any realistic way to restore function of the horn , but I do see a likely hood of flames if I were to to continue to apply power.

There is something significantly wrong in that circuit. As I said earlier, someone has wrenched on that old horn before me, tried and failed to fix it I’d wager, maybe even made it worse.
It’s been educational and enjoyable, but I’m throwing in the towel.

Thanks again.

I wonder if an ultrasonic bath would help clean it? I have one on order and will start using it next week.

Don

I’m convinced that there’s short circuit, the field stays hot when the points are open and parts get smoking hot real quick.

Kaput.

all it takes is a simple small break in the windings for it not to.

I tried.
I’d rather have a vintage horn than buy new.
I’m thinking of hunting through a nearby boneyard , maybe pull a horn(s) out of an older Buick or Cadillac, , but I’m leery of just wasting more time on the workbench.

Take a battery and some jumper wires with you and test the horns in situ. Are you looking for something from the 50s or any good sounding used horn?

If you aren't looking for "period correct" horns, the twin horns from a '92-96" F series pickup are compact, Hi-Lo, and loud. They sound like all American horns used to sound from the mid 50s to 2000.

Your description of “like all American horns used to sound” is just what I’m looking for.
I was thinking of carrying a rechargeable starter pack for field testing. That should work, yes?