Started working on the battery horn for my 21 T Touring rebuild this afternoon. As you know its the standard 6 volt battery horn for the 17-25 T's.
Bought it at Chickasha 2 years ago and never really checked it until today. The coil is good but after one Wannnek no more sound. Looking down the tube I noticed some cracks in the middle of the diaphragm. Checked the points and cleaned the contacts and etc.
If there are cracks in the diaphragm I was thinking it would still work. Nothing yet. They are fairly simple but I must be missing something.
You mentioned that you "checked the points and cleaned the contacts". OK. Grab your meter and check for continuity from "power in" to "power out", the ground point. As I recall (always subject to doubt) these have a closed circuit when not energised. When you power them, the coil becomes energised and that pulls the points open. The open points cause the coil to now be unpowered and the points close. This back and forth of the points hits the diaphram and causes the honking sound.
I hope that some of that makes sense. Good luck with your project. Bill
The diaphragm is almost always filled with pin holes from water getting into the front snout. The Battery horn actually was not introduced until the first part of 1922. I make the new reproduction horns and they are made to factory drawings for all but the motor parts so the diaphragm, brackets, motor cover...etc all will interchange with original so if you need anything new other than the motor, I probably can help you. I make the new diaphragm out of stainless steel so it won't rust out. The horn was adjusted for maximum loudness at a draw of 5 amps from a 6V battery. Check the gap between the end of the horn plunger and the diaphragm since it should be 1/32" This is actually easy to set. The plunger is threaded at the motor end with 10-32 thread so loosen the lock nut and back the plunger out till when you tap on it it just "clicks" against the diaphragm. continue to screw the plunger toward the diaphragm as you tap on the end of the plunger with your finger. When all gap is gone between the plunger and diaphragm you will notice that the click has gone away. Work slowly and find the exact point of rotation that just makes the click go silent. Notice there is a screwdriver slot in the end of the plunger. Since the thread is 10-32 then one full turn back out of the plunger will move the plunger back by 1/32" of an inch. Got it?
Thanks for the information for setting the plunger. This makes things a 'little clearer' than the Ford manual.
I guess the cracks in the diaphragm were caused by the plunger over time. I plan to get another one.
If you make your own diaphragm it is made from spring steel or stainless spring steel can be an upgrade. The horn works like a snare drum in that the diaphragm must be really tight around the perimeter so that only the center vibrates. If the diaphragm is loosely suspended the horn will have a low pitch and not be very audible if it even works at all. The diaphragm is part of the whole system that pushes the plunger back and closes the points to start another cycle. There are essentially then 2 springs. The diaphragm is one and the blade springs that the plunger is suspended to are the other and the plunger goes back and forth between those 2 springs systems. Every horn is slightly different and has a natural resonance that makes it very loud if you get everything right and tight.
The horn I have is for the 22 and up T's. I had forgot the mag horns were used earlier. I have a new replacement bell to replace the rusted out one on the horn.
Looks like they were spotwelded or tacked on originally. Any thoughts?
They are spot welded in with 4 or 5 welds around the seam between the horn bel and the flange. Where did you get the new replacement bel? I am asking only because I make them and if you have one of mine then I can give you better way to do things but if someone else made it then I hate to have you do something that might prevent it from then fitting. I have the factory drawings for those parts but the maker of your bel may not.
I bought the horn bell along with some other small parts at Chickasha 2 years ago. It has minor rust in places and was a new bell that was never used. It looks to be identical to the original that I have. Don't know who made it. The ends have the same diameters as the original.
Are you coming to Chickasha? I could best explain what you need to do if you stop by my site.
We are still planning to go as long as the weather is good. Will you be bringing some small parts? If you do, a diaphragm would be appreciated. Thanks
I can bring you a diaphragm. They are made of stainless steel and you don't want to try and rework that item with small tools ha ha. The way the bel is removed assumes only that the flange portion of the horn/bel combo is solid and not rusted near through. If the flange portion is heavily rusted and thin in places then you won't end up with a horn that works because it won't hold the perimeter of the diaphragm tight. You should note that the old and new bel have a seam in them. That seam should be at or near the bottom when the horn is mounted on the car. The seam may be a spot welded seam with the metal overlapping about 1/4" or so or it may be a rolled seam done by a machine. Both are per Ford drawing. The Ford design actually had a bead that was rolled into the small end of the bel to prevent it from being inserted too far into the flange while replacement bels usually omit that detail because your horn might be made by other companies that Ford bought from.
What you do first is to take the horn apart completely until you have only the flange and bel assembly as a single unit consisting of 2 pieces spot welded together. This usually means drilling out rivets around the entire perimeter of the horn. What you do next is to use a hack saw and cross cut off the old bel at a distance of about 1/2" away from the flange surface. Thus you leave about a 3/4" wide piece of the old bel in place so far including the 1/4" inside the flange lip. Next part is kinda tricky. Find the spot welds that are holding the remnant of the bel to the flange and find the 2 that are furthest apart. Very carefully hacksaw the bel material between the 2 spot welds but don't cut into the flange. Your blade from your hacksaw may be hand held or you can usually have enough clearance to take the blade form the hacksaw and put it back in the hacksaw with the blade protruding through the hole in the bel/flange portion. Work very slow and cut so that you end up with a sheet metal "end" of the band of metal that is the old bel. Now bend that end up and grab it with the side jaw of a heavy needle nose pliers acting just like a key on an old coffee can you are trying to open. Now roll the metal up onto the outside of your needle nose pliers. At each weld as you peel the old metal bel out, the metal will peel up and leave a small hole in the band and a small head of metal at the weld. Don't worry about that yet. Just keep peeling the old bel out. If it breaks off completely at a weld then saw between the next 2 welds as before and grab one end of the sheet metal and keep peeling. When you have all the old metal bel peeled out you will have some stumps sticking up that are remnants of the old spot welded bel that are still part of the flange. Use a file or grinder and file away those stumps being careful to leave the flange surface rounded in there. I used a round sanding drum with rubber core in put it in my drill press and work it around the inside perimeter of the flange/bel mating surface. When you have all the stumps filed down your new bel can be inserted and will cover the old weld places. Rotate the bel to put the seam at the bottom and spot weld it in place in about 5 places. I have done this procedure many times and if you are patient it is easy to make the horn look perfect. If the bel ends protrude into the horn flange cavity do not try to cut them off but just take a small hammer and gently peen them down flat against the inside of the flange surface. Work your way around the horn flange and you will then end up with a smooth funnel shape going from the flange down into the bel.