Anti theft horn- '69

[Jeffrey S.]

Hello All,
I have posted before that the alarm horn on my '69 failed this year. I removed it and bench tested it with 12 volts and it would sound and then slowly fail. So I decided since I had nothing to lose I would try to open it up and see what the failure is. In was amazed that the internal parts all looked brand new. The covers and plates were pitted. Below are 2 pictures of the 3 sections and a picture of the main internal parts. My question is- what makes the horn sound? I would like to try to get it working but more than that I want to get an education. Thanks for any help.
Jeff

[Jimmy P.]

Re: Anti theft horn- '69

Hello All,
I have posted before that the alarm horn on my '69 failed this year. I removed it and bench tested it with 12 volts and it would sound and then slowly fail. So I decided since I had nothing to lose I would try to open it up and see what the failure is. In was amazed that the internal parts all looked brand new. The covers and plates were pitted. Below are 2 pictures of the 3 sections and a picture of the main internal parts. My question is- what makes the horn sound? I would like to try to get it working but more than that I want to get an education g. Thanks for any help.
Jeff

Hi Jeff,
I did the samething with my 73 alarm horn. I sanded and cleaned the pitted areas as best I could. In the main part ( your second picture ) there are contact points under that flat bar. Mine were dirty and not making good contact. So very carefully I used one of my wife's finger nail files to slide between the points a couple of times to clean the contacts. You can also see that the adjusting screw tightens down on the flat bar opening and closing the points. You need to loosen that so you can turn it all the way in both directions. Helps with tone too! As for how the horn works, you can also see the copper wire winding in this same part. The center vibrating plate fits down inside the hole with the plastic lining. Make sure to clean the metal off in the hole carefully for good contact. Be careful not to damage the plastic. This acts just like an electromagnet. When power travels through the wire winding it causes the center plate to vibrate rapidly, thus causing the horn to sound. To keep testing mine I used a couple pair of vise grips to hold the unit together in a vise. If you get it to vibrate steady after adjusting the screw it will sound once you put it back together with the horn. ( Note: It took numerous attempts at adjusting that screw to get the horn to sound properly.) Now, if you get it to vibrate you can put it back together. You'll need to make another gasket, or use a tube of gasket maker, that's what I used. I'm sure you ground off the rivets, so they are not reusable. I went to Lowes and bought the cap screws pictured below. This size works perfectly. This process worked for me, maybe I was just lucky. But my alarm has been working fine for the last three years. Hope you get yours to work. I know there are guys on here who restore these for a living, and may do things differently. Especially replacing the rivets for judging. But I, like you wanted to see how they work. If, however your wiring is broken somewhere (no continuity when checked) then it will never work. I had this problem, with another I tried to restore. But you say that yours did sound, so your wiring should be ok.
BTW, I test the alarm system a couple times a month just to keep it working. To keep those points from sticking together. Just like keeping you clock working by not disconnecting the battery. Disconnecting the battery for long periods of time lets the points on the clocks stick together too! But that's a horse of a different color!
Have fun, hope this helped!

[Jeffrey S.]

Re: Anti theft horn- '69

Jimmy,
Thanks so much for your response! The important thing you have told me is that the center plate is what makes the sound when vibrating. I will check the points for pitting/corrosion. I have completely removed the adjusting screw so I know I can get any adjustment necessary. I have excellent continuity through the coil, the wires look nice and the plastic is good and solid. I intend to make a gasket from gasket material and temporarily hold the unit together for testing with some nuts and screws. I will try to get the same screws you used to replace the rivets and fill the sockets with epoxy. Once painted black they won't be distinguished from the rivets. The original rivets are not usable since I cut the unit apart at the edge with a Dremel tool, slicing the rivets in half. I will post the results when I finish.
Thanks again!
Jeff

[Russ S.]

Re: Anti theft horn- '69

Jeff, Did you attempt to adjust the screw before you cut it apart? Often times a slight adjustment of the screw weather it is a regular horn or an alarm will get it working again without damage to the horn.

[Jeffrey S.]

Re: Anti theft horn- '69

Russ,
I did try to use the adjusting screw. I could get the horn to sound using the 15 amp setting on my battery charger but it would sound for a few seconds and then fail. I take these things as a challenge and learning experience. I have cleaned, de-rusted, and tested everything and am now ready to put it back together. Here's hoping.
Jeff

[Jeffrey S.]

Re: Anti theft horn- '69

Thanks for all your responses. I re-assembled the horn after cleaning and de-rusting everything. It now works perfectly!
Jimmy- Thanks for suggesting the socket head screws. I compared the socket head screws you suggested and found that the head was significantly larger than the rivets but an 8-32 was perfect. Thanks again.
Jeff

[Jimmy P.]

Re: Anti theft horn- '69

Great to hear that it works. There is no better feeling than doing it yourself. Now that you know how to restore it you can pick some up cheap to repair and keep as a spare or resell. That's what I did.
Regards,
Jimmy

[Floyd B.]

Re: Anti theft horn- '69

What is the note of the alarm horn. Should it sound like the forward horn low note, forward horn high note, or somewhere in between?

Thanx

[Jimmy P.]

Re: Anti theft horn- '69

What is the note of the alarm horn. Should it sound like the forward horn low note, forward horn high note, or somewhere in between?

Thanx

Floyd,
Its definitely not the low note sound or the high note. Can't really explain, its pretty "sick" lol! Maybe an in between If you'd like to PM me your cell# I'll be happy to record mine and text it to you, and you can decide....

[Floyd B.]

Re: Anti theft horn- '69

Jimmy,

That's funny. "Sick" is a perfect description of what it sounded like before it quit. If reconditioning the innards gets it working again, I'll just set the screw half-way through its range of travel and call it "close enough."

Thanx,

-Floyd-

[Don L.]

Re: Anti theft horn- '69

What is the note of the alarm horn. Should it sound like the forward horn low note, forward horn high note, or somewhere in between?

Thanx

Floyd, do you know how a musical trumpet sounds when it's played with a mute installed in the end of it? I'd liken the alarm horn to that of a muted trumpet. Just imagine stuffing your forward horn with a shop rag. As Jimmy says, it sounds kinda sick. It certainly wouldn't alert me to a theft if it was activated for its intended purpose.

Hope this helps.

[Jeffrey S.]

Re: Anti theft horn- '69

Floyd,
It is actually a very pathetic bleeping sound- like a sheep bleating. DON'T PUT 12 VOLTS ON IT FOR MORE THAN A FEW SECONDS AT A TIME- YOU WILL FRY IT!!!
Jeff

[Floyd B.]

Re: Anti theft horn- '69

Well... no dice. I was able to free up the adjustment screw on all three horns but all I could get was some feeble static out of each horn. I took one of the forward horns apart and it looked to be in about the same condition as Jeff's horn innards. The copper windings look good and I used an emery board to lightly clean the points. Still, no toot, just some static.

I don't know what to do next.

[Patrick H.]

Re: Anti theft horn- '69

I don't know what to do next.

https://www.carhornrestoration.com/

[Floyd B.]

Re: Anti theft horn- '69

I had more success today than yesterday. I took a much more disciplined approach and completely reconditioned all the parts, mildly filed the contact points, made new gaskets from grocery bag paper and took care during reassembly to make sure the pole piece was centered in the coil and not touching the electromagnet. I got all three horns to toot. The forward high note (246) and alarm horn sound about correct but the volume isn't strong. The forward low note (245) toots but the pitch is too high and the volume is weak. There is a very small range of setting for the points. Just 1/8 of a turn in either direction and I only hear weak static. Another 1/8 turn and I get no sound at all. It takes quite awhile (and a lot of trial and error) to find the sweet spot.

I also noticed that once I got them work - the more I used them the better they sounded. I'm not sure why. Perhaps they perform better when they are warmed up?