Horn dead spot

Bob Johnson

Bob Johnson

Well-known member
My horn sounds good when it works. But sometimes it just will not turn. If I take off the cover and rotate the armature a little bit it works fine. It seems that if the armature stops at certain spots the horn will not work. When it is on a dead spot sometimes the ammeter will move when I press the button sometimes it does not. I have cleaned the armature, put in new brush springs, Lightly lubricated the bearings, moved the adjustment screw in and out. The brushes appear to be aligned. I even tried shorting the ground terminal of the horn (sometimes that works). It does not happen often when the engine is running but occasionally it does. I have also tried backing off the adjustment screw several turns so the motor will run without any resistance. Sometimes even with the motor free it will not move unless I rotate the armature a little.


Any suggestions.


Bob
 
Mark the good contacts on the armature with a magic marker and test with horn button as a starting point. Rotate the armature to the next contacts and test with button. If still good mark it with the marker. Once again. Rotate and test and mark. You will then be able eventually to identify the dead contact. Then check that you have a good solder connection on that contact. Also check that it is clean and makes good electrical connections…. This finds most of these intermittent horn issues.
 
Here is what I found. If I rotate the armature to put the brushes in the middle of contacts the horn works. However if it is set where the brushes are in contact of 2 adjacent contacts the horn will not work. What now?


Bob
 
There are quite a few videos online that show how to test the connections on an armature.

I would think that is where you would start for your horn.
 
Check to see if the new brushes move freely in their holders.

You can check the armature with an ohm meter. Check each segment of the commutator. Put one probe on one segment and the other probe on the adjacent segment. Go all the way around in this manner.

Are the new brushes arched to match the commutator? The new brushes can be arched to match the commutator with a little bit of fine sand paper wrapped around the commutator and moved back and forth.

Did you weather the storm OK?
 
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Bob -
I have found that sometimes the horn button and its contacts can be the problem. Rust, condensation or a build-up of gunk beneath the button interfere with it making electrical contact with the wire leading to the light switch bail and eventually to the horn. If you rotate the black plastic horn button a few degrees, that can often either scrape away the rust or place the button in a new position where contact can be established. It only takes a second to do this and doesn't cost anything. Try it and see if that makes the horn operation more consistent. If not, you're back to the horn itself.
Should moving the button solve the problem, it won't for long. You'll end up disassembling the horn button and cleaning the contacts with sandpaper. I have repaired a couple light switch rods this way that I was almost ready to give up on and replace. A little time spent cleaning the horn button and horn wire contacts saved a ton of money and gave me satisfaction to have diagnosed and repaired the problem myself.
Marshall
 
The brushes are arched. Button ground is OK. I tested adjacent segments on the armature with an ohmmeter. The resistance range is in tenths of an ohm so it is hard to measure. All but one of the measurements were between 0.1 and 0.2 ohms. One pair of adjacent segments measured 0.6 ohms. What next.


Bob
 
You may have to undercut the insulation between the copper segments on the armature, easier to do this with the horn removed.
Generators need to be undercut, starters do not.
 
If you find a dead spot in the armature then it can be rewound. There are still folks that rewind those little armatures out there.
 
Fixed

I found a cold solder joint at one of the segments. A little heat and solder now it works. Thanks to everyone for their suggestions.



Bob
 
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