Momo horn button repair help | FerrariChat

Momo horn button repair help

Discussion in '308/328' started by vaccarella, Nov 8, 2017.

This site may earn a commission from merchant affiliate links, including eBay, Amazon, Skimlinks, and others.

  1. vaccarella

    vaccarella Formula 3

    Apr 16, 2011
    2,291
    Full Name:
    Paul
    The horn stuck open today. It's a Momo steering wheel and a Momo button (did the Nardi have a Nardi button?). On the bench, it's not consistently closing circuit when pressed. Seems a pretty simple mechanism in there but how do I get inside it? I see three plastic lugs around the perimeter but don't want to experience a jack-in-the-box accident :)
     
  2. Dr Tommy Cosgrove

    Dr Tommy Cosgrove Three Time F1 World Champ
    Owner Rossa Subscribed

    May 4, 2001
    35,285
    Birmingham, AL
    Full Name:
    Tommy
    I don't think it is an expensive replacement item.
     
  3. vaccarella

    vaccarella Formula 3

    Apr 16, 2011
    2,291
    Full Name:
    Paul
    You're probably right but if I can fix the OEM easily...

    Spraying contact cleaner in there seems to have improved it no end according to the ohm meter. Can't check right now as it'd wake up the house ... or not :)
     
  4. vaccarella

    vaccarella Formula 3

    Apr 16, 2011
    2,291
    Full Name:
    Paul
    Not as simple as I first thought. I attached a meter to the air horn terminals. If I press the horn, I get ~12V. Release it and it stays @ 12. If I turn the headlamps on, the 12V @ the horn drops to 0. Thoughts?
     
  5. dflett

    dflett Formula 3

    Jun 24, 2005
    1,603
    NY
    Full Name:
    David
    Pinched or worn cable inside the hub staying grounded after the initial push?

    Bad ground near the horn? There's a ground stud near there that can loosen.
     
    vaccarella likes this.
  6. GatorFL

    GatorFL Moderator
    Moderator Owner

    Nov 18, 2005
    16,335
    Wellington, FL
    Full Name:
    Duane
    Bad relay?
     
    vaccarella likes this.
  7. vaccarella

    vaccarella Formula 3

    Apr 16, 2011
    2,291
    Full Name:
    Paul
    Thanks guys, will look at both. The visible cable in the hub seems sound enough. I'll try and eliminate stuff.
     
  8. Hannibal308

    Hannibal308 F1 Veteran
    Rossa Subscribed

    Jan 3, 2012
    6,270
    Kahuku / Cottonwood / Prescott
    Full Name:
    Will
    The OEM horns are very valuable...fix yours. I just took mine apart for one of my '77 GTBs and all you need to do is gently unbend the three metal tabs that fold over on the backside of the button. The tension from the spring for the horn button is negligible...no jack-in-box to worry about. You will find the spring and a metal plate, as well as a nut/bolt that make up the contacts for the horn button...mine were all surface corroded and they clean up super well with any mild abrasive or a scotch pad. Reassemble and test before gently folding back the tabs. The tabs are fairly robust and I Image Unavailable, Please Login Image Unavailable, Please Login wasn't too concerned about them breaking, but I would avoid many fold events nevertheless.
     
    vaccarella likes this.
  9. vaccarella

    vaccarella Formula 3

    Apr 16, 2011
    2,291
    Full Name:
    Paul
    Well, it isn't the relay - checked with another working one & same symptoms. The switch at the horn looks good & shows correctly with a meter. So I'm now looking around for the earth. But wouldn't that trigger the horn all the time if it was the fault?
     
  10. thorn

    thorn F1 Rookie
    Silver Subscribed

    Aug 7, 2012
    3,322
    Tallahassee, FL
    #1 Rule in vintage Ferrari electronics: start with the ground wries. Even if it "looks and feels" solid, check it on the meter. (Just because a ground wire is connected to the chassis doesn't mean it's actually grounding... trust me.)
     
  11. vaccarella

    vaccarella Formula 3

    Apr 16, 2011
    2,291
    Full Name:
    Paul
    I still have a horn stuck problem & maybe my multimeter readings at the relay socket today will give a clue:

    With horn off:
    • I see 12.3V across 86 & 85
    • and 12.7V across 86 & 87
    • All others read 0V
    When the horn is depressed:
    • I see 12.7V across 86 & 85 (and the value returns to 12.3 when released)
    • I get an ohm reading between the horn terminal at the back and the steering wheel boss.
    • All other values are the same as when horn is off
    Could the problem be at the carbon/copper slip ring / brush at the steering wheel? I tried turning the steering wheel as far as is possible when stationary but no change in symptoms.
     

Share This Page