Help - Bosch Snail Horn Restoration

[tom1394racing]

I am attempting to restore the Bosch snail horns for my 70E project. The two I have reserved for the project vibrate and hum when I apply my 12 volt/3amp power supply but no horn tone.

I took a 3rd horn I have in my stash to do a practice restoration before I tackle the more pristine horns I have saved. This 3rd horn did nothing when I applied power to it so I dissembled it, cleaned it up and used my wife's nail file to clean the contacts. I then checked to make sure the electromagnet, the switch contacts and diaphragm all worked properly after I adjusted the contact position using the adjustment screw on the back of the horn body. I could not figure out how to remove the resonator plate from the main snail body so I was only able to clean the inside surface. After reassembly, this 3rd horn vibrates and hums just like the other two but still no horn tone. I then took an unused aftermarket snail horn, that had been sitting for 10 years plus, from my stash and tried it on my power supply. At first it hummed and vibrated just like the other three but then I gave it a firm knock and it sounded off a horn tone and continued to perform correctly afterwards. No such luck with a knock on my original Bosch horns.

Take a look at my photos. What am I missing? I am guessing that it must be something in the resonator plate that is stuck. Any suggestions on how to remove it without destroying the snail body?

[blucille]

A couple of things. Probably all obvious.

First. Anyone notice. The mechanical/electrical bits of these and the fanfare horns are identical except the mounting stud?

Did you supply power with sufficient current. The draw is quite high.

With power applied, I slowly turn the adjusting screw until you go from a hum to a honk.

Aside from that, I’ve done the Emory board trick some more and then more adjusting and I’ve had nearly 100% success.

[SIMI BOB]

Use a good battery to test the horns. 3 amps probably not enough.
Bob B

[Noah]

I need to dig into my horns as well. Which is the adjusting screw?

[TEC69E]

Interesting . . . I'm in the middle of resurrecting my bosch snail horns too. Initially I had no power to the electromagnet but solved that after cleaning the points. Then had a weak honk which got much better after cleaning the corrosion on the resonator plate and the horn body. Could not get my adjustment screws to turn so just left them alone. But did use a multimeter to make sure I had all the volts (13.2) from the battery to the magnet.

Btw, I would be interested in buying your spare/extra snail horns/parts to finish my project.

[BrentF]

From my successful experience in restoring a pair of faulty snail horns, you have to install paper gaskets on either side of the diaphragm, as this affects the spacing of the trigger mechanism on the diaphragm relative to the contacts on the points.

Tom: I have this snail horn that doesn't work for spare parts. PM me if you're interested

[SIMI BOB]

See here for more on the snail horns, along with a description how they work.

http://www.early911sregistry.org/for...093#post882093

Bob B

[tom1394racing]

Mine still only issues a low frequency hum even when I connect it to a fully charged battery. Moving the adjusting screw does not seem to make a difference. I am guessing that the resonator plate is not being excited by the vibrating diaphragm. Is there a way to remove the resonator plate from the snail body to clean it?

[stevesob]

Here is a helpful thread on this topic on the Bird:

http://forums.pelicanparts.com/porsc...storation.html

Steve

[tom1394racing]

Use a good battery to test the horns. 3 amps probably not enough.
Bob B

Like Bob said. I connected my restored horn to the battery in my Honda Ridgeline. With a little tuning of the adjustment screw, all is good. My reserved, pristine horns also sounded great.

Thanks all