Info needed: Ford CMP horn- diaphragm replacment or repair

[Jacques Reed]

Good Day,

Does anyone know where to obtain a new or repro horn diaphragm for the Ford CMP trucks Part No. 78-13812?
The one pictured has been perforated by rust which only became evident after a good chemical cleanup.

I tried the usual vintage Ford parts supplier as it appears to be a standard Ford part and not specific to the CMP's, ie. no asterisk in the parts list. Plenty of horns but no parts for them.

Alternatively can they be repaired? I thought about brazing it but it is spring steel and may destroy the temper. Solder, though a cooler process, may be too soft and fall out when it vibrates. Any epoxy material will probably do the same I would think. Anyone used any of those processes with success?

Any help gratefully received.

Cheers,

[Lynn Eades]

Jacques, It you repair it the tone might be poor?
I have found that many horns are the same p.c.d. You may be able to introduce the whole deal (electrics and diaphragm) from another horn?

[jack neville]

Jacques, PM sent

[Ganmain Tony]

Jacques,

In my humble opinion, I reckon the damage will be negligible on the horns ability to function.

The hardest thing youve got in front of you now is getting it back together.

My experience is not extensive but I just pulled apart and repaired my F15 horn.

It has not functioned for years and looked rough when I pulled it apart. Simply gave it a gentle clean with compressed air, found a broken wire and after a couple of attempts soldered a broken wire I found in the internals.

It now has a nice, obnoxious blast.

Yours may be in worse condition but I am always amazed at the robustness of components of this era.

[Jacques Reed]

Thanks all for your inputs:

Yes, I too felt repair might alter the tone especially if heat was involved or some material was attached.

My biggest concern was water getting through it into the electrics but unless I got caught in torrential rain the chances would be negligible.

I might just put it back together and live with it. I guess if you drove like a Mexican taxi driver, always on the horn, the diaphragm might fail quickly from fatigue starting at the holes. Sensible use of it should see it last a long time.

Here's a handy hint for getting the nuts off the screws that hold the horn front to the coil plate:

Those screws will turn when loosening the nuts as there is nothing to prevent it. After a good wire brush of the nuts and exposed threads, and lots of penetrating oil I clamped each screw in the vice from the head to the threaded end to prevent turning and then backed off the nuts until they contacted the vice jaw protectors. I used plastic vice jaw protectors for a bit of grip and prevent damaging the ends of the threads. After that the last few turns were easily done. Also keep adding penetrating oil and work the nuts back and forth a few times before removing from the vice and it will ensure the last few turns of the nut are easy. Strange design for a screw but I guess the designers never though someone would be taking it apart 75 years later.

Attached photo of horn before disassembly. Surprisingly, despite the rust, there was no holes in the rear cover of the horn after it was cleaned up.

Cheers,