Wednesday, November 10, 2010

Horn(s) Repaint and Repair

Volvo P1800 (1970) Lucas 9H horns
The horns and their bracket suffered from surface rust, and at the very least needed to be repainted. Interestingly, only the top half of the horns rusted. It appears that the bottom and top of each horn are made from different metals, the top portion being steel. The bottoms must be pot metal  (anyone? )or just have a much stronger plating that remained intact.
In situ, before removal. Note, the rust is only on the top casting of each horn.

Top of the upper horn marked "L"( inside the horn), also stamped 69211B on the top, Lucas 9H on the bottom. The lower horn is marked "H" in the bell and 69205B on the top.

I used sandpaper was used to clean up the flat or gently curving areas; a Dremel tool was able to get into more complex portions. A dark grey primer and flat black paint finished up the job. The bracket definitely had a flat finish, the horns themselves may have been more of satin, oh well.  Before doing all this, it would have been wise to test the horns... You can see what's coming next....
Using a hand drill to drill out the old rivets. Use of the hand drill was easier than getting out an electric drill and should lower the carbon footprint of the project.

As is ends up, one horn was fine, but the other would not sound. To make things more complex, the horns are riveted together. The rivets were relatively soft and where easily drilled out with my wife's help, she held them on the coffee table while I drilled with an eggbeater hand drill. More caution should have been used pushing out the rivets after the tops were drilled out, I bent one of the flanges over the bell. At least I was able to pound it back into shape for the most part...
New gasket and role of gasket material from NAPA.
     The original gaskets appeared to be some kind of felt paper. When wiped with a paper towel saturated in alcohol, a brown residue stained the towel, much like tar. I'm guessing these were a tar impregnated paper? My mechanic thought there were rubberized. One gasket could be reused, the other was replaced with a homemade gasket traced from the bottom half of the horn. The "rubber-fiber" gasket from NAPA was 1/32th of an inch thick (NAPA part number FPG3157 or on Amazon, thicker than the original and I suppose not ideal. Luckily this gasket was for the bell side of the horn and therefor will not effect the solenoid spacing. A RG-59 "F" connector with the outer shell cut off, and the inside tube sharpened made an impromptu hole punch. The inner tube on RG-6 "F" connectors was too large.

Home-brew gasket, home-brew hole punch,  ceramic hammer, and sharpening supplies. The punch (shiny part, center of the photo) is a RG-59 "F" connector with the outer shell cut off revealing the inner sleeve.  The distal edges of the tube were sharpened using diamond files and oil stone to creat a sharp cutting edge.

The solenoid side of the horn.

Once opened, the contacts could be cleaned with doubled over sandpaper. The contacts were slightly misaligned, but I did not try to bend the spring steel back for fear of breaking the whole thing.

Bell side of the horn.
Horn components showing proper orientation and order of assembly.

As per my mechanics suggestion, I used a VERY light coating of Ultra Black gasket RTV to coat both the old gasket and the bell side flange.

Here it the horn put back together. The new paint was removed from the upper surface surrounding the rivet holes to ensure electrical continuity between the top and bottom of the horn. The horn body is the ground for the system and therefor must be electrically continuous from the horn, through the bracket to the car chassis. Stainless steel screws and nuts were used in place of rivets, sorry purists.
Mounting bracket seen from the bottom. Although not listed as separate parts in the manual, the metal washers were not well attached and fell off when I tried to clean them up with a wire brush. Oddly, there was a different kind of paint under them (primer?). 

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