Speedometer Question

Discussion in 'Sportster Models' started by 1Qtswede, Jun 25, 2008.

  1. 1Qtswede

    1Qtswede Member

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    Hi guys, newbie here in the forum.... had a question I was hoping one of you fellas could help me with. I was on a ride the other day, and my speedometer quit working. Odo was still rollin with no problems, but the speedometer just quit. I am trying to learn the ropes to deal with it myself, so any help you can suggest, I would LOVE to hear! Thanks!
     
  2. Dr. Dolittle

    Dr. Dolittle Experienced Member Staff Member Moderator Contributor

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    First, welcome to the forum!

    Second, if you're going to try to do any work yourself, you've got to get ahold of the service manual for your bike. If the dealer doesn't have it you may have to resort to Ebay or Amazon or Craig's List.

    Sorry I can't help you more but there's some real mechanically minded folks on here who will jump in very shortly.

    In the mean time, you can honestly answer "no" when a cop asks you, "Do you know how fast you were going?"
     
  3. TattoodITGuy

    TattoodITGuy Member

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    Welcome to the forums...

    off the top of my head, no. but i will be reading my service manual tomorrow and if i come across an answer ill let you know.
     
  4. glider

    glider Veteran Member

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    If the odo is working and the speedo isn't, good possibility it's the speedo head itself.
     
  5. Jcannon

    Jcannon Member

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    My good lord Glider your like Albert Freakin Einstein. Never ceases to amaze me.

    BTW: Welcome to the forum.
     
  6. glider

    glider Veteran Member

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    Been doing it since 1969, now if I could just remember everything....:D
     
  7. 1Qtswede

    1Qtswede Member

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    I've already got the Clymer service, repair & maintence manuel, but it just doesn't cover anything more than the electrical side of things, I"m wondering if it's a cable issue... I've ordered another manuel, but I'm just itchin' to get it goin.....probably be another week or two before the book comes in...dangit.
     
  8. glider

    glider Veteran Member

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    If the cable is intact and turning and the gear drive is OK and the ODO is turning, it's more than likely the speedo head or the ODO wouldn't work either.
     
  9. scottaudio

    scottaudio Member

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    Not being a factory trained HD mechanic, I'm going to base this answer on the information presented so far in this thread.

    I am guessing that in 1994, the speedometer is fed by a cable that is connected to a gear somewhere in the drive mechanism, whether it's to the front wheel (common in motorcycles) or elsewhere.

    Newer HD's use a sensor in the transmission that sends electrical pulses to the speedometer head, as well as other modules on the bike including the tilt and turn signal module.

    Cable driven speedo's have been around since the dawn of cars and bikes, and the cable spinning in the middle drives two things inside of a speedometer: gears that are directly tied to the odometer, and an air/fan type of clutch mechanism that drives the needle to indicated speed.

    This mechanism is much like the unit used in an automatic transmission as well, but essentially try to imagine two fans facing each other. One is turned on (the side driven by the wheel of your bike) and it starts spinning. The air created by the movement blowing on the other fan blades will start them turning in sympathy. Now, if you were to put a spring (like a clock or watch spring) on the blades of the second fan, they could allow the blades to only spin so far until the spring is tightened. The spring is calibrated so that depending upon how fast the first fan is spinning, the second one will go further (greater energy transferred causes more movement). Hence, through this type of calibration, you have a speed indicator.

    Now, after that simplistic description you can hopefully understand how the speed indicator part of a unit can fail (the fan transfer mechanism fails) and yet the turning of the cable still direct drives the gears on the odometer part.

    If you can get inside the unit easily, you might find that some dirt or something is affecting the fan assembly that drives the needle. But, these are highly calibrated units that can easily be thrown way off kilter unless you know what you are doing. That fan assembly is really spinning fast, and the bearings over time will give out.

    Most likely, unless you can find something simple, you will need a new assembly.

    Good luck! Steve Scott
     
  10. 1Qtswede

    1Qtswede Member

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    Very cool answer. Better to understand a little, and I will see what can be done. I got the bike from my Dad, and he told me he'd replaced the head last year, so, I'm thinking to simplify things, maybe just replacing the whole kit & kaboodle would save me some futzin' around.... we'll have to see how much that'll run...:newsmile107: