Modern Vespa

Wondering if anyone could give some advice on the difficulties of rebuilding an old horn? I have an '74 Super frame that was made for the American market. So it has the larger horn diameter than a European large frame. I can't get it make any sort of noise and I have measured that the switch is putting current through the horn. I haven't been successful at tracking down a american diameter horn so I was wondering what it would take to rebuild it, or just clean it up internally.

Has anyone pulled apart a horn assembly and rebuilt one before? I want to understand what it takes before drilling out the rivets that are currently holding it together and potentially wrecking the thing.

How did you measure how much current is flowing through the horn? Or, to look at it a different way, what was the resistance of the horn coil (resistance between the two terminals)? I would guess that it should be less than 100 ohms; more than 1000 ohms could be an open circuit.

Inside the horn there should be a switch that breaks the circuit when coil pulls the diaphragm, then closes to reactivate the coil causing the diaphragm to vibrate. That switch may be worn out or dirty.

I've never had to look at a Vespa horn, but I've taken apart some old car horns long ago.

Have fun!

Before drilling out the rivets and taking it apart, try soaking the whole horn in a bucket of solvent or gasoline. This usually frees it up to get it working.

There are two types, AC and DC , with the DC ones having the little breaker switch like a set of points and creating the continuous on-off-on-off which creates the nice quack that your horn finally makes. AC does this all by itself and needs no such switch. I'm surprised your bike came w/ the big horn, my '68 Super has the small one stock. The big one came on Rallys and Primaveras and a few other smallies that I've ever seen and nearly all are 6V. I have an '80 50 special with a 12V big horn though. It just kinda squeaks some of the time, but not reliably.

Lots of ppl have rebuilt horns here, try a search and see. I think one guy even stuffed new horn guts and back into a wrecked horn that still had a nice front.


Same horncast I believe, but small horn stock.

I like the suggestion about soaking it in solvent. I took one apart a few years ago and actually got it to work. Unfortunately I didn't take any pics, but once you get it apart, you'll see how it works. Don't worry about wrecking it... drilling the rivets out is a snap and it's easy to put back together with new rivets.