VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1929-1932 31 horn

Regardless of the amount of adjustment, my 31 coupe’s horn is not very loud. It beeps, but not loud enough to be heard by another car. Is there a part subject to wear?
Thanks,
Sid

It is possible for the diaphragm to weaken by corrosion or damage. Or the electromagnet may weaken. I don't recall either of those occurring in the number of horns I have messed with.

Sid, if you have a multimeter , you might want to check to see if there is any contact between the 2 electrical contact studs and the body of the horn, instead of the full current going to the electromagnet. Set the multimeter to OHMs with the BEEP.

Sid,

Another thing to check is the gap between the electromagnet core and the steel adjusting screw in the center of the diaphragm. It's adjusted by loosening the lock nut on the adjusting screw, turning the screw in or out until the sound improves, then retightening the lock nut. You have to remove the chrome grille to get to it and adjust it.

All the Best, Chip

Thanks guys. I’ll check it out in the next few days.
Sid

I adjusted the gap as Chip suggested. I reinstalled the grill, reattached the horn to the light bar, and the horn would not blow. I took it apart, and found that one of two small metal discs at the points was broken. Is there a source for that part? Is there someone who rebuilds horns? By some miracle are they now being reproduced?
Thanks,
Sid

As far as I know those horns are not being reproduced. You will probably have to find a 1931 parts horn to get the part that you need to repair your horn.

Is there a motorcycle horn that would be same size I could steel parts from?
Sid

Harley Davidson motorcycles, Plymouth cars and maybe others used the same type of horn. Some have the contact studs in different locations and mounting brackets. The internal parts are the same. I have rebuilt several for myself and so far have only had to make insulators for the connection studs. I am sure that other repair parts time is coming.

Sid,

I have few part horns, can you attach a photo of the part you need?

Dave

Dave, the back is the part I need. It would include the points and electrical connections. Sorry, I can’t remember how to post a picture.
Sid

Dave, I can send you an email with pictures. Please provide address in a PM.
Sid

Sid,
Just remember the backs can differ significantly particularly in the location of the electrical contact studs and shape of the mounting brackets.

Thanks Chipper.

I got another back from Dave, reassembled the Horn, and adjusted it. It honks great with the 2 terminals hooked to 6 volts, but when hooked to the 2 horn wires, and horn button is depressed, nothing happens. When the 2 horn wires are hooked to my volt meter and the horn button is depressed, it reads 6 volts. I checked continuity and found no connection between the terminals and the case, but I do have continuity between the 2 terminals. Any thoughts?
Thanks,
Sid

There should not be any conductivity between the terminals and case. The circuit is basically battery to one terminal on the horn, other terminal to ground. That powers the electromagnet. The magnet pulls in the vibrator plate which has a stud to open the points when pulled in. That breaks the circuit returning the vibrator plate and points to their original position. The repeated oscillation of the vibrator plate produces the noise.

I sounds like a weak ground that is strong enough to give you a voltage reading on the meter but too weak when trying to operate the horn. If it worked on the bench, it should work in the car. A good easy way to test is ground a piece of wire to the chassis and put it to the terminal on the horn that has the wire from the horn button attached to it. If the horn is good, it should operate. If it doesn’t, run a new wire from the positive post on the battery to the positive post on the horn while leaving the ground test wire attached. If it then blows, your positive power wire is bad and won’t carry enough amps to run the horn.

I had a similar problem on my 32 sedan, I had to increase the wire size to # 12 then it worked fine.

Thanks guys. After running the test wires the horn blew, and when I hooked the original wires to it again it blew while pressing the horn button. Now I just need to re-work the bracket to make it look like a 31 and I’m done. I appreciate your help.
Sid

I straightened the bracket, painted the back, installed the horn on the car, and it wouldn’t blow. With a meter I determined I had a good ground connection, but only 3 volts going to the hot side, which made no sense. After pondering the situation for a few hours, I started checking other circuits. I found the headlights didn’t work. In recent months this has happened before, and wiggling the fuse helped. But this time it didn’t. I checked the fuse for continuity several times. About every fifth try it would connect. I replaced that fuse and suddenly the horn works. A full 6volts is now going to the horn. Why is this? The 1 fuse the car originally came with (on the headlight switch) and it affects the horn? The car has a new wiring harness from YnZ that includes turn signals. I don’t see how that additional circuitry could affect the horn either.
Sid

Check out your wiring diagram and you will see how the fuse and the horn are connected.