Horn Repair Procedure - 1959 #9000352 - NCRS Discussion Boards

Horn Repair Procedure - 1959 #9000352

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  • Richard M.
    Super Moderator
    • August 31, 1988
    • 11323

    Horn Repair Procedure - 1959 #9000352

    Years ago I rebuilt my #352 Driver Side horn in my '59. It stopped working some time ago. I can hear it tick a bit internally but that's it.

    To remove the horn on a '58-'60, raise the hood and insert a bolt into the hood support slider holes for added "anti-arm-crunch" safety. Remove one grille tooth and mask the chrome to protect it from scratches. Remove the power wire from the brass terminal. There is a 5/16-18 bolt holding the horn to the inner upper cowl which is threaded into a riveted nut plate. There will be a ground wire ring terminal attached to the bolt, along with a toothed washer to ensure solid ground to the horn bracket. Work the horn out of the toothless grille opening.
    0207210845_resized.jpg

    The backside of the horn mount nut plate. Mirrored view shown. This view was from the Driver Side wheel well area above and forward of the harness heading toward the Head Lamps.
    P3180012.jpg

    Note on a '61-'62 you'll have to remove the entire grille from it's mounts and tuck out of the way to access the horn bracket bolt.

    I used the Paragon rebuild kit then which came with 2 new diaphragms, gaskets, rivets, etc. Unfortunately it is not available now. I only used one diaphragm then and never installed the supplied rivets. I used screws to hold it together as a instructed test and decided to leave it that way if it ever failed. I'm glad I did.

    Paragon Kit
    0207210846_resized.jpg0207210847_resized.jpg




    The stud is originally riveted to the original diaphragm which is usually badly rusted. The rivet gets cut off of the stud, which is then drilled and tapped for a 1/4-20 screw. Loctite is used when assembling. The thick washer must be reused.
    0207210849a_resized.jpg

    Here it the contactor. When the horn is energized, the stud gets pulled down into the coil electromagnet. The outer edge of the contactor is then pushed down, opening the circuit to the coil. The spring action of the metal diaphragm then pulls the stud back up, then allowing the contacts to close again. This action repeats very quickly, causing the diaphragm to vibrate and sing it's tune out through the trumpet.
    0207210855_resized.jpg

    I tested the contactor with a simple ohm meter. The contacts had continuity, i.e. shorted, but when I placed a piece of paper between them, there was still a short. The plates of the contactor are separated by insulators. I suspected they failed or rust had migrated between the plates.
    0207210855a_resized.jpg

    I used a soldering gun to remove the coil wire from the contactor. I then drilled out the 2 rivets holding the contactor and removed it. There is a tubular cardboard insulator on the large rivet to insulate it from the horn case. This side gets connected to the negative side of the coil. A fiber washer and plain washer is used at the rivet head on the outside of the case. A hard grommet is used on the inside as a spacer(upper left).
    0207211345_Burst01_resized.jpg

    The smaller rivet on the right of the contactor is the ground point source from the horn button ground via the horn mount bracket. Power is applied(via the horn relay) to one coil positive end as shown on the upper right inside the case. The other side of that is the brass terminal for the harness power connection plug.
    0207211349_resized.jpg

    Note the rust at the contactor mount areas. I cleaned that area to bare metal before reassembly.
    0207211349a_resized.jpg


    I used my grinder to remove the peened ends of the rivets and punched them out and cleaned the pieces on a wire wheel. I also filed the points to clean their contact areas.
    0207211450_resized.jpg
    0207211449_resized.jpg

    There was a crack in the fiber insulator and it broke so I made a replacement from some fiberglass sheet of the same thickness. It acts like a spring so it has to be durable.
    0207211450a_resized.jpg

    In order to isolate the contactor plates from each other I used small plastic insulator spacers. I have a variety of these for my electrical repairs. My plan was to use screws and nuts instead of rivets to reassemble the contactor.
    0207211506_resized.jpg

    The other side showing the tubes of the insulators.
    0207211506a_resized.jpg


    Assembled with small stainless steel screws and washers to replace the rivets.
    0207211516_resized.jpg

    Locknuts with integrated toothed washers. I added a dab of green Loctite to the joints. It's the thin type made for external application and goes down the threads.
    0207211517_resized.jpg

    I installed the contactor back into the case using a screw, washers and locknut on the insulated side(left) and re-soldered the coil wire. After testing I'll use a tubular rivet if I can find the right size. It's a tad smaller than a #10 screw so I didn't want to drill the case or contactor leg larger. At the smaller contactor leg I added a toothed washer between it and the case and used a rivet to attach.
    0207211554_resized.jpg

    Other side of the case after assembly.
    0207211554_Burst01_resized.jpg

    I reassembled the trumpet to the case using the screws and nuts as before. I tested and it worked fine after I adjusted the tone using the screw. It adjusts the contactor assembly position which moves the position of the points fiber spring with respect to the diaphragm stud for optimum sound. It's has a unique 12 point screw head. I use a 12 point 1/4" socket from a kit I use for damaged bolts. Craftsman #3307.
    0207210914_resized.jpg

    After testing I decided to open it again and changed some hardware. I used a small slotted pan head screw instead of that temporary Phillips screw. i ground down the head to make it look more like a rivet. I then painted the entire horn after masking the brass terminal post and it's fiber base. Note to leave the bolt mount area free of paint. I used a small piece of square tape there before paint.

    Here is the final assembly. After some continued tests I may replace all screws with rivets and use sealer on the gaskets.
    0209211254a_resized.jpg

    0209211253a_resized.jpg

    0209211255_Burst01_resized.jpg


    Rich
    Last edited by Richard M.; February 11, 2021, 06:05 AM.
  • Richard G.
    Extremely Frequent Poster
    • July 31, 1984
    • 1715

    #2
    Re: Horn Repair Procedure - 1959 #9000352

    Rich;
    Great write up.
    Thanks for sharing.
    I thought rebuilding a horn would be simpler than it is.
    Only issue, for me, would be the sheet fiberglass and the diaphragm if it's cracked.
    Not sure how I would source either one it it is was required.
    I have a couple junk value horns to practice on. May be a good source for parts?
    I might even try this some day.
    Here on the Left Coast the only time I use a horn is in the Operations Check.

    Rick

    Comment

    • Richard M.
      Super Moderator
      • August 31, 1988
      • 11323

      #3
      Re: Horn Repair Procedure - 1959 #9000352

      Originally posted by Richard Geier (7745)
      Rich;
      Great write up.
      Thanks for sharing.
      I thought rebuilding a horn would be simpler than it is.
      Only issue, for me, would be the sheet fiberglass and the diaphragm if it's cracked.
      Not sure how I would source either one it it is was required.
      I have a couple junk value horns to practice on. May be a good source for parts?
      I might even try this some day.
      Here on the Left Coast the only time I use a horn is in the Operations Check.

      Rick
      Thanks Rick. The strange thing is why this contactor failed short circuit. It appears that the rust actually migrated inside the insulating sleeves of the 2 rivets holding the base plates together. This caused the short. My notes say I rebuilt both horns about 13 years ago. I'd been caught in the rain many times and washed the car many times so I'm thinking that added to the issue. I didn't use sealer on the gaskets. Since I didn't rivet them it was easy to open this one up. During diagnosis I went through about 4 or 5 iterations of dis/re-assembly. Again I decided no gasket sealer just in case.

      I have not seen the diaphragms available anywhere. Not sure why Paragon stopped selling them. It was a nice kit. That contactor fiber sheet acts like a spring so any similar sheet of tough laminate could work. Maybe thinning out a piece of Formica on a belt sander is a option. If you need any of those little plastic insulators for the contactor plates, I have a good supply and would gratis you some if needed. But I think mine shorted out was a unusual case which may not happen very often.

      Rich
      PS I edited the post and added a few more photos of the finished horn.
      PPS For the record, I spent quite a bit of time working on this horn and now understand why it is very costly to get them repaired at outside repair vendors. You'd think it's simple work, but it really isn't. I think it's easier to rebuild a generator..... than a horn.

      Comment

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