Horn repair and worn commutator
 

I have a horn that works intermittently and was wondering what things to check to determine whether a horn needs a full rebuild vs just a cleaning and lubrication? Any indicators that might suggest the field coils needing to be rewound?

Sometimes when the horn works it will work for a few seconds and then just quit. It will randomly work again later, but sometimes it is minutes, other times it is days. I am wondering if the commutator is part of the problem as it is quite worn. Is this repairable? Can it be turned down, or at this stage would it be best to just try and clean it and run as is? Is it okay to clean the armature and field coils? Would this do any good?

The car has an alternator and was rewired a couple of years ago so the wiring is good. Not saying that the problem cannot exist in the wiring, but I am thinking the problem is in the horn itself.

Thanks!

Re: Horn repair and worn commutator
 

Does it spin freely?
How are the brushes?
Take the cover off and hook it up to the car. Use the horn until it doesn't work. Is the armature still spinning but there is no sound, or is nothing happening? Alternately, use a multimeter on the connections instead of installing the horn, while you press the horn button. Does it provide 6V each time?

How is the condition of your horn button? Not fluent with A horn buttons, but do they ever get dirty and gummed up?

On my T I had an intermittent horn. Turns out the horn wire I bought had a break in it!

Yours DOES look very worn, but I'm thinking as long as there is metal, it should work. It either works or it doesn't. If the top commutator seems greasy to touch you could always degrease it and maybe lightly sand if needed. Or, just use a multimeter touching a brush connection and then one on the commutator for continuity.

Re: Horn repair and worn commutator
 

While pushing the horn button and with the horn motor spinning lay a small piece of fine grade sand paper against the commutator and shine it up. Often this is all that is needed.
If after doing this your horn doesn't spin on demand hook it up directly to a battery to see if it works. If it does then your troubles are probably in the wiring to the horn or that commutator is just too worn.

Re: Horn repair and worn commutator
 

I have two Model A’s which I have owned since 1989. On both cars the horns worked only when the engines were running fast. All I did was to spray some nonflammable electrical cleaning fluid on the commutators while they were spinning. Next, I sprayed a little oil on the bushings. Both horns are loud whether the engine is running or not. I repeat this procedure about every two or three years. I should note that the commutators are not as worn as the one pictured.

Re: Horn repair and worn commutator
 

I don't know about all the different makes of horns but the Stewart Warner horn I have had the commutator segments delaminate from the armature shaft. This gave me a chance to see that they are relatively thin pieces of copper that were likely formed from sheet copper and given a slight curvature so that they could form a circular shape when attached to the shaft with some form of resin.

I would be afraid that they are too thin to use an armature lathe on them since the segments are very thin. I'm not sure what procedure they used when attaching them to the shaft but I'm sure it could be recreated using modern materials that can take the potential heat that builds during operation. Folks don't usually run the horn for a very log period so it likely doesn't get all that hot. It is more of an intermittent use electrical device for the most part. There may be some folks that actually overhaul these armatures but I don't know.

If it has a good connection and wire to the generator (which is relatively short) then I'd have a good check of the grounding area and the wiring for that ground that runs from the horn to the button. It may have a dirty ground or it may have a broken wire that just touches at each end of the break. A wire like this should have higher than normal resistance when checked with an ohm meter.

Re: Horn repair and worn commutator
 

Push the horn button and work it back and forth under pressure. The contacts do get dirty.

Re: Horn repair and worn commutator
 

Your commutator is quite worn but the likely problem is that the bushes are not making contact all the time. Try moving them in their holders to make sure that they are not binding and that the springs are pushing them to make contact.

The comments by the other are all valid. Either bench test the horn or use a volt meter to find out which wire is hot and then short out the other terminal with a short length of wire. That will bypass the horn button and associated wiring. It will also verify that electricity is getting to the horn. The contacts where the wires connect to the horn could be loose or corroded. If the horn works by bypassing the horn button then you know that the horn is good and the fault is in the button or wiring. If the horn is bad and you cannot make it work by fiddling with the bushes then you will need to look around for another horn or send it out to have it rebuilt.

If the armature turns but no sound then try adjusting it. Turn the adjusting screw in one click at a time and try again. If the adjustment screw is in too far it can keep the motor from turning.

Re: Horn repair and worn commutator
 

Do the brushes have a fair amount of pressure against the commutator?

Re: Horn repair and worn commutator
 

I'd try a parallel set of wires to the horn to eliminate wiring as a cause...I've chased many a problem that turned out to be wiring related...almost impossible to detect an intermittent open in a wire.

Re: Horn repair and worn commutator
 

An intermittent wire will always have higher resistance than it should. I've never had a problem finding a bad conductor wire. It's harder if you don't have a multi-meter and have to rely on replacing wires one at a time.

Re: Horn repair and worn commutator
 

just got my stewart warner back, from steve smith in morristown indiana. excellent service.

Re: Horn repair and worn commutator
 

As worn as that commutator is, I'd look for another if you determine the armature / commutator is your problem.
Others have mentioned spring tension on the brushes as perhaps not being adequate. I would disagree - the only thing that would cause that commutator to wear that much would be excessive spring pressure.
Look also at the brushes themselves. The brushes should be wearing more than the commutator.

Re: Horn repair and worn commutator
 

My two cents to add to this are that there looks to be no mica in between the the horn 'wedges'. Great scientific/engineering term huh? So it is possible that there is arcing but I think she is due up for a rebuild.

Mike

Re: Horn repair and worn commutator
 

The ones I've seen don't have mica between the segments. These things were made at a time when a person could replace the whole horn for a relatively low price. Those little series wound motors are pretty basic units. The only thing I found on my old Stewart Warner was the resin that held the commutator together with the shaft. It was basically just glued together. The steel core segments are the most complicated part of the whole armature. Some of the manufacturers may have made them better than others. Ames, EA Labs, GIM, Sparton, and Stewart Warner all made horns for Ford. The GIM types were the only ones that had bushings and a 5/16" diameter armature shaft but they aren't as common as the Sparton and Stewart Warner horns.

Rebuilders should have the stuff to completely rebuild the armatures.

Re: Horn repair and worn commutator
 

Please tell me more about steve smith in morristown indiana. Does he have a regular business in the repair of vintage horns, I have a couple that need refurbishment.
Please provide contact info for steve
Thanks
Lon

Re: Horn repair and worn commutator
 

I would send it out for a rebuild. I fried mine and bought a new A&L horn.

Re: Horn repair and worn commutator
 

Mr. Smith has an add for horn & wiper armature repairs on the MARC site.
Steve Smith, P.O. Box 505 , Morristown, IN 46161. Email: [email protected]
I've not done any business with him so I can't vouch for his capability but I've not heard anything bad about him.

Re: Horn repair and worn commutator
 

Hello guys. I'm lost on the technical talk on restoring my horn. What I have is a chrome plated ahoogah horn. Does anyone know someone who actually rebuilds them?

Re: Horn repair and worn commutator
 

Do you know who rebuilds them?

Re: Horn repair and worn commutator
 

I had the same problem with an original horn I bought from ebay that supposedly was "remanufactured". I replaced the brushes, brush holders, terminals, and insulator. Sanded the commutator to shine up the copper, but no more. A couple drops of oil top and bottom. The horn seems to work fine now and sounds great.
I also replaced the diaphragm, gaskets,and adjustment spring after verifying it worked. I found out the adjustment is touchy. 1 or 2 notches either way and it goes from motor spinning with no sound to the motor not turning at all. In between great sound.
I notice your contact terminals are deformed. You may not be getting good contact.
They really are not that hard to work on.