Hella B31/6V Horn Restoration

[OLDveedubs]

Well, after much research and trying to find information I decided a picture tutorial of rebuilding this 6v horn may help others in the future!

First, the resources I used for this were the Bentley manual which has very basic instruction.

Here's a good video on the basic principles of how this horn works and troubleshooting.


Link


This website is often referenced on Samba posts but is no longer working. Everett posted the text detailing a refurb in this thread.

Here's another solid write up on a Ghia horn refurbishment.

I set out to show a step by step refurb of this early horn. Enjoy!

This write up is for an eight bolt horn.

The 6 bolt horn is a little different but uses the same principles.

They both have the same part number, the internals and number of bolts is all that is different.

First the pieces, from left to right, top to bottom.

*Two paper gaskets. Some horns only come with one.

*The contact point set.
--Diaphragm activator/points isolator
--Top arm points
--Bottom points
--Spring
*Terminal blocks, rubber seal, and securing screws (one with seal).

*Horn body
*Metal rectangle washer
*Paper rectangle gasket
*Coil
*Paper insulators

*Adjusting screw spring
*Adjusting screw spring bottom plate with captive rubber washer. Can be replaced if necessary.

Diaphragm parts (top to bottom)

*Stud
*Electromagnet small
*2 brass washers
*Electromagnet large
*4 brass washers
*Diaphragm (in the center you'll see a black washer, under it is a rubber seal)
*Washer
*Nut

*Not shown
--Cover
--Mounting piece horn to body
--Nut for mounting piece
--Adjusting screw

To start, I thoroughly cleaned each piece. Soapy water for the housing, media blast for the tough metal parts, and Scotchbrite pads for the smaller pieces.

I used some brake cleaner on the outside of the housing and my understanding is they were assembled, then completely painted black from the factory. Some paint came off and you can tell a difference in texture which you can see in some of the pictures of the back of the housing. IF you want to avoid this I recommend either not using a strong solvent or using a stripper to remove it all. I didn't mind the additional character.

Reassembly

Housing and metal washer

Followed by paper washer

Coil goes in

The securing bracket shown in the left of this picture is tight. I found a small screw driver and some patience allowed me to bend it (it is spring steel) to put the coil in. Make sure to use the insulating paper under the bracket as seen in the pictures below.

Here is the back of the housing. Notice the texture differences showing the bakelite vs painted material.

Next up is the terminal posts. They are designed to go in only one way. This allows the hole for the positive and negative wires to be on the outside of the horn when installed.

Notice the offset hole.

Another offset hole. These need to match up. There is also a very small piece of paper that acts as an insulator which also goes down into the hole. If it is missing or unusable it is no big deal.

The rubber was a bit stiff so I used a light coating of silicone caulking to try and help waterproof the horn.

This is the screw and washer which connects to what I am calling the negative side of the horn. There is no positive or negative side it can be hooked up either way.

Installed on the bottom of the image. The black heatshrink was to replace some of the rotten paper style insulator which had corroded on mine. I also used some dielectric grease to help prevent corrosion.

Next up is the "positive" or contact side. This is the securing screw and rubber seal.

Here is a breakdown of the contact points.

*The paper insulator goes on top of the coil. I found putting the paper on the inside of the coil and using a small dab of super glue helped prevent it from moving.
*Spring
*Bottom points
*Diaphragm activator/points isolator
*Top arm points (actual points are on the other side of this piece)
*Securing screw.

Some points to mention.

1st - clean the points! I used a small file and some Scotchbrite pads to get them even and clean.
2nd - the adjustment of the diaphragm activator is critical. The above video shows it and you'll also hear it if all you get is a "clunk" when you test your horn.

Link

The frequency is just me touching the wire to the battery.

But that clunk basically is the magnet being pulled down but not touching the diaphragm activator to release the contact points allowing the diaphragm to spring back up which starts the cycle again. Adjusting the diaphragm activator will fix this problem!

All together.

Notice the paper insulators under the coil securing bracket and contact spring.

The diaphragm activator has been adjusted to stick out past the top arm points.

The adjusting screw, bottom plate, and spring are not installed in this picture.

The diaphragm goes together how it came apart.

Things to remember:
*The large electromagnet is what actually comes in contact with the diaphragm activator. The thin metal wings right in the middle, either side of the center hole is what touches the diaphragm activator. You can see it is even chamfered a bit to allow smooth operation.
*The electromagnet must be aligned in a specific way with the diaphragm itself to allow the screws to secure it to the body and the electromagnets to match up with the coil setup in the bottom of the housing. Small adjustments will be necessary so don't tighten the securing nut until you've test fit it in place.

The rest of the assembly is straight forward. Install the adjusting screw, bottom plate with rubber washer, and spring. Tighten these down so when the diaphragm is place in the housing it sits slightly high on the horn body. This is a good starting point and will then allow you to adjust the screw from there. For my worn out horn I had to tighten the screw multiple turns until it was almost impossible to turn. This allowed the best quality and loudest sound to come from the horn.

I used both of my original paper cover gaskets. Cleaned them up with a bit of brake cleaner.

Any thoughts, comments, or questions be sure to let me know. Good luck with you project!


Link

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"Perfection through inspection."

[bluebus86]

nice write up. nicely done photos too.


I might add to your warning on solvents, that avoid harsh solvents on the electric coil as the wires have an insulating varnish on them that might be harmed by some solvents.


again nice write up.
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[fly2kads]

Wow, thanks!

[flyboy161]

Perfect timing. I have an old horn or two to clean up and this write up is perfect! Good job!
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[boinkffd]

Great info. Thank you

[EverettB]

Great!
Thanks for detailing this process
I added a link to the Beetle FAQ
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[chrisflstf]

Excellent write up

[MillerMachining]

I realize this is an old thread.

Recently picked up a couple B31/6 VW 6 volt 6 bolt Hella screw terminal horns.

Wondering if anyone knows when/where 6 bolt horns were used as opposed to 8 bolt. (both pictured in this thread).

Thanks

[Wyatt Earp]

Thanks very much for this OLDveedubs.
I tooted the horn on my 1965 Ghia when I passed my friend John Moxon a couple of weeks back. He then got in touch to say that he thought he could only hear one of the horns working. He was right, the lower pitch one (tief) did not sound. Using your superb, very detailed instructions, I was able to get it repaired and working again!
Many thanks.

[RustPatch]

Bringing this one back up.

I'm starting into my B31/6 Hella but the adjustment screw is corroded. I've got a few newer, spade terminal Hella horns and the adjusting screw hole seems to be covered with something. Am I missing something and there's something covering the screw or am I going to have to drill the head of it off?

[alexism311]

Hi. I know that this is a very old thread, but I’m wondering where you got that rebuild kit for your horn? I’m looking to rebuild mine as well.

[67conv]