Prestolite Horn Demystifed
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.
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.