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Hot Rods Weird Speedometer question

Discussion in 'The Hokey Ass Message Board' started by blazedogs, Feb 27, 2020.

  1. blazedogs
    Joined: Sep 22, 2014
    Posts: 457

    blazedogs
    Member

    I'm old and don't adapt to changes too well or understand a lot of new features , or in many cases I don't want too. For years all my old cars that I have had I used a speedometer that run off a cable that went down to the transmission , most cases it worked just fine. But now the speedos don't need a cable which now is the desirable way to go. Can you explain to me how this works in layman's terms ? Gene
     
  2. squirrel
    Joined: Sep 23, 2004
    Posts: 46,902

    squirrel
    Member

    Which specific speedometer are you talking about? There are a few ways to do it...
     
  3. blazedogs
    Joined: Sep 22, 2014
    Posts: 457

    blazedogs
    Member

    Jim I,m just reading the ads and most of the ads mention no cables. Have't really paid any attention to any speedometer specifically that they mentioned since I don't have any interest except what I have been using in the past, the old basic cable run speedometer
     
  4. Stonebird
    Joined: Dec 19, 2008
    Posts: 108

    Stonebird
    Member

    A common way uses a sort of electromagnetic sensor on the trans output shaft. The sensor generates electrical pulses as the shaft spins and is wired to the speedo. The speedometer calculates pulses per mile and converts them to a MPH reading on the dial. The speedometer is programmable so any tire size and rear gear ratio works and can be reprogrammed if you change gears or tire size. Others use GPS and aren't connected to the trans at all.
     
    Last edited: Feb 27, 2020
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  5. jimmy six
    Joined: Mar 21, 2006
    Posts: 7,181

    jimmy six
    Member

    We are streeting an old drag and land speed car and are going to use a sender on the Richmond Super T-10 speedometer cable connection and an electric speedometer. The original dash insert has 4 SW gauges and the Tach is mounted center of the dash.
     
  6. blazedogs
    Joined: Sep 22, 2014
    Posts: 457

    blazedogs
    Member

    Very interesting, technology is advancing rapidly I just ordered a speedometer from Summit, bought the old analog type, but was reading about the different ways speedometers are functioning now. Thanks !
     
    lothiandon1940 likes this.
  7. From what I know about them and that's very little they work like a GPS ( Global Positioning System ), We use Garman GPS in out delivery van's, and it will locate what your looking for, calculate the time it takes to arrive and shows you how fast your driving. HRP
     
  8. PhilA
    Joined: Sep 6, 2018
    Posts: 800

    PhilA
    Member

    I find it fascinating that these things work at all; the GPS ones have all manner of sensors inside on a microchip that would have previously required sprung weights, gyroscopes and magnetic compass readers (that would also have needed to been manually set and calibrated with each use).
    The GPS ones know exactly where they are on the face of the planet within about 3 feet, what direction they are facing, how fast they are accelerating and which way up they are. That's more data than a lot of light aircraft have.
    All so you can avoid getting blue lights in your rear-view. Any new all-screen cellphone has all that inside also. I can clip my phone up on the dash and have it read out the speed and direction I'm traveling. Yes, it's all black-magic voodoo, but you gotta admit however it does it, it's pretty impressive.

    --Phil
     
  9. squirrel
    Joined: Sep 23, 2004
    Posts: 46,902

    squirrel
    Member

    Think of it more as how ships navigated in the old days...you could get your latitude by using a sextant and observing the angle (north/south) of the surface of the earth, relative to a star in the sky. You could find your longitude by observing the angle of that star (east/west), and knowing exactly what time it is. GPS uses time, and knowing the positions of the "stars" (actually the GPS satellites themselves), to find your position. The trick is getting the receivers and clocks with the required accuracy all stuffed into that tiny chip.

    The non-GPS electronic speedometers are rather simple by comparison. They just have a sensor that detects the output shaft of the transmission moving and display that rate as your speed.
     
  10. PhilA
    Joined: Sep 6, 2018
    Posts: 800

    PhilA
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    Agreed. The fact that the chip can lock to multiple signals that report where they are in the sky, performs differential timing analysis, and trigonometry in real-time is amazing. The solid-state accelerometers and magnetometers fascinate me though. I like being able to take things apart to see how they work, and these I cannot so they remain magical and mysterious. That's good enough for me.
     
    harpo1313 likes this.
  11. Just use a cable.

    I am not real familiar with a lot of the electronic speedometers. Some of them that I am familiar with are GPS which many of he fellas swear by. I know a little bit about GPS and am not that impressed with it. for example NASA this year had to make a major adjustment to the GPS satellites they got moved around by a major solar storm and were not accurate enough for the surveyors to use for making surveys. How long before anyone noticed? That is how long your GPS speedo was not accurate.
     
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  12. squirrel
    Joined: Sep 23, 2004
    Posts: 46,902

    squirrel
    Member

    Your GPS speedo was still accurate. But your absolute position on the earth, to the nearest inch, was not.

    I prefer mechanical speedometers on old cars, they're so much more fun to set up, and to keep working.
     
  13. alchemy
    Joined: Sep 27, 2002
    Posts: 15,875

    alchemy
    Member

    Says who? All my speedos have cables, just like my distributors have points and my brakes have shoes.
     
  14. If the satellites were not accurate I don't see how the speedo was accurate. They don't all blow the same direction or the same amount in their orbits and it takes information from more then one to make the proper calculation. granted logic to me is not the same as to everyone else. :oops:

    We for the most part are using transmissions that have a provision for a cable and I see no reason to not use a cable. But I also don't see the need for a speedometer so if what I am building doesn't already have one or buying a cable is not on todays agenda I don't bother. I do find a tachometer to be an essential piece of equipment though. ;) :D
     
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  15. squirrel
    Joined: Sep 23, 2004
    Posts: 46,902

    squirrel
    Member

    If you were measuring the speed to 6 digits of accuracy, then it might be off at the last digit...but probably not.
     
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  16. blazedogs
    Joined: Sep 22, 2014
    Posts: 457

    blazedogs
    Member

    Guys, all I wanted was a simple answer about speedometers Now I have a headache ... Just kidding .Thx for the answers ... Gene
     
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  17. studebakerjoe
    Joined: Jul 7, 2015
    Posts: 712

    studebakerjoe
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    Blaze, these newer non gps speedometers aren't really new tech they are more a case of using older tech in another place. The sender in the distributor of a 61 Studebaker Hawk for the tach works similarly to the new speedometer senders. You're just measuring shaft speed of the transmission output instead of the distributor shaft.
     
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  18. jetnow1
    Joined: Jan 30, 2008
    Posts: 1,598

    jetnow1
    ALLIANCE MEMBER
    from CT
    1. A-D Truckers

    I have lost the signal on my gps to many times to want to use it for a speedometer. I am sure it works for most people most of the time, but I will keep on using a cable.
     
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  19. ramblin dan
    Joined: Apr 16, 2018
    Posts: 2,150

    ramblin dan

    I am seeing more of these GPS speedos and am probably going to run one in my project car as there are more coming out that look more vintage.
     
    Cosmo50 likes this.
  20. Re: GPS speedos, what happens when you drive in a (long) tunnel? Do they quit, like a navigator (at least the ones I’ve tried)?
     
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  21. goldmountain
    Joined: Jun 12, 2016
    Posts: 2,234

    goldmountain

    I plan on building a car who's transmission has no provision for a speedometer drive so I'm thrilled with the idea of GPS.

    Sent from my SM-T350 using The H.A.M.B. mobile app
     
  22. When "telephone poles looked like a picket fence" is a good gauge one is going fast.
     
  23. GTS225
    Joined: Jul 2, 2006
    Posts: 1,173

    GTS225
    Member

    Yup, they will. If the transmitter/receiver in your car looses comm signals with the satellites, it'll fail. Once you're out of the tunnel, it'll link back up in about 60 seconds, and things will be good again.

    Roger
     
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  24. You can get yourself into situations where a certain combo of parts seems impossible.

    This little gizmo will generate the needed signal to drive an electric speedometer on anything with a differential.
    CD7D3DF7-6021-4650-BF87-DE33B93735B5.jpeg
    4CDD5F33-69B2-4384-B8BC-F063784D3243.jpeg

    And for whatever off topic reason you may need a vehicle speed sensor signal
     
    Last edited: Feb 29, 2020
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  25. squirrel
    Joined: Sep 23, 2004
    Posts: 46,902

    squirrel
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  26. Mr48chev
    Joined: Dec 28, 2007
    Posts: 27,545

    Mr48chev
    ALLIANCE MEMBER

    Hell my 98 BMW drives the speedometer off on of the brake sensors. Thing is spot on accurate according to the speedometer app on my phone though.
    I'll run a cable drive on the 48 if I can hook one up reasonably simply and somewhere in my boxes of crap I have a couple of speedometer calibration boxes that by changing some little quick change looking gears I can get it pretty close to right on the money. finding a cable that fits the trans of choice and speedo of choice may be fun though.

    I think at issue here is that a lot of us have built our cars where the actual design of chassis parts may not be conducive to running a cable without issues. The awe crap moment when you wake up and figure out that your great looking tube X member is right in line and only a very few inches away from the speedometer drive on the side of the trans. That other moment where you figure out that that "extra" hole you filled was the only spot that the speedometer cable could be routed though the firewall to connect to the speedometer and there isn't room behind the dash to have it bent in a curve without binding.
    That later model trans that flat doesn't have a cable drive provision and none are available for it at any cost.
     
  27. You are correct. Surveyors need to be closer than an inch.

    I will give the GPS speedos this, they are easy to set up. basically plug n play. A cable speedo can be a crap shoot being that some transmissions have several speedo drive gears and changing gears or tires can have a big effect on accuracy.

    When you could still find them in the wrecking yard some early '70s era Oldsmobiles used a speedometer drive off the front hub. I liked those because gear changes didn't effect them.
     
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  28. squirrel
    Joined: Sep 23, 2004
    Posts: 46,902

    squirrel
    Member

    Vw also used the speedo cable of the front wheel

    Sent from my Trimline
     
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  29. s55mercury66
    Joined: Jul 6, 2009
    Posts: 3,980

    s55mercury66
    Member
    from SW Wyoming

    I think that a lot of Ford 8.8 rear axles have a tone ring on the differential carrier that drives the speedo, starting somewhere around the 1991 model year for those who may be able to use that.
     
    partssaloon likes this.
  30. 37slantback
    Joined: May 31, 2010
    Posts: 398

    37slantback
    ALLIANCE MEMBER

    I was searching for some speedo stuff and came across this thread. A guy I know has a 59-60 Studebaker Lark with a 327 and Turbo 350. He said he disconnected the speedo cable because it was reading crazy high. I don't know his 8in rearend ratio or tire height.
    So from T350 to stock speedometer there is probably a gear adaptation out there that would let him get his stock speedometer back?
     

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