Vespa Horn Rebuild - Anyone?
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Joined: 05 Oct 2013
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Location: Santa Cruz, CA
Sun Dec 01, 2019 5:02 pm quote
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.
Ossessionato
BV350, Primavera 150, Yamaha Zuma 125
Joined: 06 Jun 2013
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Location: The Twin Cities of Minneapolis/Saint Paul, Minnesota
Sun Dec 01, 2019 5:23 pm quote
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!
Molto Verboso
Vespas 1964 GS160, 1965 SS180, 1977 V9A1T, 1983 PX150E
Joined: 16 Apr 2011
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Location: Siam
Sun Dec 01, 2019 5:52 pm quote
chilidog wrote:
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.
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.
Veni, Vidi, Posti
74 50s x3 78 P200 84 Cosa 58 AllState 68 Sprint 80 50special + projects
Joined: 22 Nov 2010
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Location: seattle/athens
Sun Dec 01, 2019 5:56 pm quote
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.
Ossessionato
1976 Super (x 2), 1974 Primavera (x 2), 2006 Fly 150
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Location: So Cal
Sun Dec 01, 2019 6:17 pm quote
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.
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