Prestolite Horn Demystifed

[Dana67Dart]

I was parts picking the other day and found some 67 dart horns.

There were 2 hi tone and one low tone.

The price was right so I got all 3.

Figured I had a better chance of a working horn if I had 2 of each.

Well one would not vibrate at all and had high numerical resistance like in the low mega ohms. The other 2 became functional after some persuasion and their resistance was in the 1 to 10 ohm range.

So what do you do with a non functional horn???

Take it apart!

Horn before disassembly.

To get it apart I drilled out the swedged pot metal points around the horn. Coincidentally there was a dimple in the center of each swedged post.

Once apart I found a bunch of rust in the chamber where the coil is. Unfortunately I did not get a photo of that.

The coil (green), pitch control (red)and breaker point (yellow)

The contacts were the source of the high numerical resistance and once cleaned the coil energized fine.

Back side of the coil etc. This one had a screw, the other 2 had a hex head bolt for the tone control.

This is the diaphragm. This side faces the horn body. It has a seal on it to the horn body but no seal from it to the coil holder, probably how moisture got in to make all the surface rust and flakes

This side faces the coil.

The gold colored ring around the center is a fiber washer. As the magnet coil energized it pulls the center of the diaphragm toward it and the fiber washer pushes down on a contact point and breaks the voltage to the coil. The coil releases the diaphram and it moves back to its resting position allowing the contact point to reconnect and apply voltage to the magnet coil again starting the cycle all over again .

This is the horn body where the diaphragm's sound gets amplified

All in all a pretty simple device.

With some rust removal and drill and tap the swedged posts it could be re assembled to a working horn.

 

[67Dart273]

Yup. The contacts are almost always the problem, but sometimes it gets worse. Water intrusion can really make a mess, and perhaps unrepairable. On my 01 Dodge Cummins, one horn was built and mounted so that the horn pointed up--a "perfect" storm for road splash to get into the horn and never get out. I found another Dakota horn kicking around here, but they are in conflict for tone. I think they are both high. I'll tell you WHAT it sounds like heck but you WILL pay attention, LOL

 

[toolmanmike]

Yup. The contacts are almost always the problem, but sometimes it gets worse. Water intrusion can really make a mess, and perhaps unrepairable. On my 01 Dodge Cummins, one horn was built and mounted so that the horn pointed up--a "perfect" storm for road splash to get into the horn and never get out. I found another Dakota horn kicking around here, but they are in conflict for tone. I think they are both high. I'll tell you WHAT it sounds like heck but you WILL pay attention, LOL

This is a great thread and deserves to be a sticky. Nicely done. I am not very musical but I bet the notes the dual horns are not harmonizing with each other. LOL

 

[Dana67Dart]

This is a great thread and deserves to be a sticky. Nicely done

I have a hand full of "Demystified" posts, day night mirror, heater blower motor etc

 

[Syleng1]

Where is the smoke pod?
I always seem to let the smoke out of those and always wondered where it came from. Nice job on this detailed process. Simple but delicate at the same time.

 

[67Dart273]

Sometimes, all you really need to do to get one going is to mark/ note where the adjuster was, and then vigorously turn it about a half turn each way while it is powered. This often "self cleans" the contacts up enough that they will work.

 

[Dana67Dart]

I have not tried this but there are programs for Smart Phones that will listen to a sound and give you the frequency.

Do that on a known good horn then tune any other to the same frequency.

 

[Syleng1]

I have not tried this but there are programs for Smart Phones that will listen to a sound and give you the frequency.

Do that on a known good horn then tune any other to the same frequency.

Yes. Great idea! We have a baby grand piano in our living room. The lady who tunes it once a year uses her I phone. She can duplicate any key and tone. I don’t play so I do not follow. Well- I can play chopsticks. lol!
So if they have that program you know there are others.
Syleng1

 

[barbee6043]

Horns?? old guy with oldMoar.... Inspection guy said, "Horn"> don't work....I yelled out the window HONK! He said louder I said " GET THE F@@@ OUT OF MY WAY!!"