XK Horn Rebuild or Replacement?

5 years ago I sent my XK horns out to some individual in Massachusetts who was supposed to be “the” horn guy in the US (apologies don’t remember his name now). At a Concours this past weekend I was told by the judges that my horns were not loud enough and not the right tone. I checked with Taffthehorns in the UK and Taff had a stroke and isn’t rebuilding horns any longer and the person who took over for him doesn’t have any extra XK140 horns.

Is there anyone you can recommend for rebuilding these horns or helping me set the tone (assuming there is some way to do so) or is there somewhere to purchase a proper replacement? TIA!

Even NOS ones can be a problem. I installed a set on my car where the originals went missing due to a previous owner. I thought that as they were new, they should work fine. No go at all for the both of them. I learned that the contacts on both had oxidized over the decades such that they wouldn’t pass any current at all – even though they looked pristine. A few passes with wet/dry fine sandpaper made them sound as good as new per this video:

In JCNA events the horns aren’t viewed for authenticity. They are only heard and must have one low tone and one high. E Type horns are readily available and inexpensive

The subject once came up on the pre-xk forum.
Here is a Lucas Windtone on my '38 SS.
Basically it’s an electromagnet that pulls the diaphragm to make the sound, and a set of points that makes and breaks electrical contact.
The sound is adjusted by the small nuts on the shaft where you see the 1/4" wrench.
The points can be filed with a thin points file as you see the file placed in the photo.

BTW they should be marked HI and LO and should sound like a tonic and 3rd chord, like playing C and E on a piano.

They are designated as Lucas HF1748, and some Jag Lover has an in-depth webpage on rebuilding them, and much other factual information

try Google, or I will look for it in all my info, I think the dude was a poster here

I have several, and they all work, as in “make a sound”

I was debating to attend them as they are original, but getting the screw out of the alloy bodies to separate them would require heat and patience

Yours should come apart easily if they have already been apart

We had two horns and a horn relay for a 1953 Bentley rebuilt by East Coast Jaguar, 802 Naamans Road, Wilmington, DE 19810, 302-475-7200, jaguar1355@aol.com. I was very happy with service and their work.

Googling Lucas HF1748 gave much info, including this

Lucas HF1748 Horn Restoration - YouTube

Thanks for all the replies, I’m going to pull my horns off the car and test each individually and together as shown in the video and see what I can come up with.

These are so simple to repair and adjust (depending on neighborhood), and so unlikely to wear out… I‘m even willing to bet the procedure is in the manuals? I did mine, later type 9H horns. Riveted, but similar. It’s less about the tone, more about the amplitude.

Ken,

If you’re referring to the Lucas horns for the late XK 120 (FHC and DHC only) or XK 140 then you have the HF1748.
You’ll find more info here, including the adjustment of these horn types.

https://www.bobine.nl/jaguar/13-electrical/lucas-high-frequency-horn-hf1748-on-jaguars-1953-to-1961/

I read that they have been opened before, which means that the most difficult step has been made (these screws can be corroded in the aluminium zinc alloy housing.

Bob K.

Thats the excellent source I mentioned, but it showed an “insecure website” warning when I checked it, so did not post the link

It sure is hard to get those screws out, I was just trying, and used a repeat heat and cool cycle with butane torch, which worked for the first couple, but the next 2 wont budge, and I burned a hole in my brand new winter tracky dacks, so I am miffed :rage:

Tony,

Same reason why I could only answer a couple of days later! Had paid a few weeks ago for the (yearly) SSL certificate but it turned out that I still had to install it myself…But now good for another year.
You may have seen on my site the difference in corrosion you’ll find on these horns. Sometimes drilling out the complete screw and re-tapping BSF 1/4" is the only answer. See this example that I called “beyond repair”. Must have spent its life at the sea side.

Bob K.

I am trying to “keep” mine but it seems to be quite difficult…!
Is there someone who has used parts missing ?

Your example is probably too far gone to consider a complete rebuild: I would search for a better starting point. Regarding parts: won’t be easy and remember that the high and low tone version have different internal parts. Don’t mix these parts as you will never obtain a good result.

Bob K.

Good point Bob i thought the different tones came from screwing the tone screw adjustment… :face_with_open_eyes_and_hand_over_mouth:
But may be here on the forum i could find some horns…? if i am lucky !

The screw should adjust the amplitude (not really, it adjusts the points) and the frequency is determined by the diaphragm etc. that likes to swing in a certain frequency.
The adjustment screw is so you can have the points to close the circuit (and thus support the diaphragm) at the right time, too early and it’s not swinging all the way, too late and it’s not working well at all.

The internals look alright to me but the steel cap seems to have gone so I‘d start with a fresher one.

note the busted out or cut screws

its a heck of a job getting the screws out of these things intact

It required repeat heat/cool cycles

As Bob K noted, if they cannot be removed, drilling and re-tapping is the alternative



So here is the first horn I pulled off the passenger side of the car. The number on the label corresponds to my “high” horn which if I understand the documented items on Bob_K1’s website it should be around 400hz. Sounded high to me, anyway I put it in a vice, attached power and it was plenty loud. Tried adjusting the screw to change loudness/pitch and got it slightly louder but seemed pretty close to max already so I don’t think this horn is the problem. I will try to get time to pull the other tomorrow or over the weekend. Can I pull out my guitar tuner and let it listen to my horn to see what frequency it registers or is there some other way to properly “tune” the horns? @Bob_K1

Ken,

That is looking like a very fine original horn you have there: June 1955!
If it works as you describe, don’t touch it and leave it “as is”.

Bob K.

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Frequency is what you get. Amplitude is what you can adjust and if they don’t sound off (just sound the horn now with the high note disconnected!) you should leave them alone. If there’s a clear problem you do them by feel as you did the high note horn and if not the judges might be the ones getting older. That or they have tested too many horns that day.
If they’re nice, don’t touch them.