How many neighbors showed up to see what you wanted? In the “throw away” world we live in today you are one of the few who stands above the rest and say “I’m gonna fix it”. Thumbs up to you. Keep it up!

Maybe a little advice to place a spring inside of the back of the air horns for better compression of the diagfhram

Those Horns Remind eme of the Nathan Airchime P2 Train Horn, Exact same sound!

wrap your hand around the edges of the diaphragm to feel any air leaking out, the metal casting is cheap and when it corrodes it breaks apart in small pieces. air will escape one way or another. you may have to sand down and apply filler on the rough mating spots to get a air tight seal again.

You have to put metal diaphragms on them because the mouthpiece that is tightening the diaphragm is made of the same material so you get a good sound and the system works better, the plastic over time marks the shape of the mouthpiece where the sound comes out And it does not sound or it sounds very low, also if you use plastic keep in mind that those horns are on top of your truck and when it is up it receives all the heat from the sun and being made of metal the horn heats up and if you put a plastic diaphragm on it with the passage of time it is spoiled and you have to be changing it ...

Do you have the info/specs on this horn. I'm trying to find one that seems to have the same pitches as yours

You blowing=name that tune lol

double up the plastic diaphragm