Speedometer vs GPS

Discussion in '1947-1954' started by 51 HHR, Mar 17, 2010.

  1. 51 HHR

    51 HHR Member

    Joined:
    Apr 26, 2008
    Messages:
    218
    Location:
    New Egypt New Jersey
    I took the truck out for a spin this weekend with a GPS mounted to see what my speed was since I have known all along that the speedo was wrong, well interesting results: at 30 showing on the speedo I was doing 50 on the gps and at 40 on the speedo I was doing 60 on the GPS.
    So now that means I dont have to worry about holding anyone up behind my truck, they must be there admiring it and those who are passing me will keep the cops busy as I drive on by.
    Bill
     
  2. mel 55_1

    mel 55_1 Member

    Joined:
    Apr 1, 2004
    Messages:
    98
    Location:
    England
    I've done this myself with similar results, though not as large an underspeed as yours.

    And, I still only have vague figures anyway, I mean even when I could drive with a constant 40 on the gps, the speedo needle would be swinging anywhere from 25 to 50. Must take that cable out and put some grease on it...
     
  3. Bill Hanlon

    Bill Hanlon Member

    Joined:
    Jun 4, 2002
    Messages:
    2,491
    Location:
    Klein TX
    Don't know if it is still so, but back in the day we always used graphite, not grease.
     
  4. Wolf

    Wolf Member

    Joined:
    Apr 20, 2008
    Messages:
    888
    Location:
    Kansas
    I need to do this also. Brand new speedo cable and rebuilt speedo thanks to a member of this board. The speedo needle bounces a bit back and forth about 10mph at the most but usually only 5 or so.

    What type of graphite do you use, like a graphite grease, and where do you get it. I didn't put anything on my cable when i installed it

    Need to check my speed with my GPS too. It seems close, but i don't know
     
  5. Bill Hanlon

    Bill Hanlon Member

    Joined:
    Jun 4, 2002
    Messages:
    2,491
    Location:
    Klein TX
    I don't remember what I had for dinner last night, much less what the graphite was. Nate'll know.
     
  6. 51 HHR

    51 HHR Member

    Joined:
    Apr 26, 2008
    Messages:
    218
    Location:
    New Egypt New Jersey
    tach cable grease

    Dont use grease there is a spray graphite pull the inards out of the cable wipe it down clean it with tri clor or similar and then spray it with graphite lube its yucky stuff dont get it on your hands use gloves
    Not sure where to get it but I would be almost positive your local General Aviation repair shop has some
    I have also been lucky with just taking the one end offf and pouring teh graphite into that end and letting it run out the other (removeboth ends) spray the graphite into a cup and then pour quickly before teh liquid evaporates
    Bill
     
  7. 51 HHR

    51 HHR Member

    Joined:
    Apr 26, 2008
    Messages:
    218
    Location:
    New Egypt New Jersey
    Speed difference

    I think my sped difference is because thetranny is not original it is a three sped on the floor from a 3/4 ton though i would have to leave that to nate or one of the other guys to school me on it I know it is the same tranny i had in mt 55.2 3800 series with teh super low first gear(granny gear) but i think the gear in teh tranny that spins the speedo is way off. The needleis steady but just that far off
     
  8. vwnate1

    vwnate1 Member

    Joined:
    Jan 1, 2000
    Messages:
    11,139
    Location:
    AMERICA !
    Speedo Service

    Use graphite grease , but before you do anything else , tape a BIG garbage bag to the seat !:eek: .

    No whining later when you skip this step as 75 % do.......

    Undo the cable from the back of the speedometer , gently lower it so it's hanging out under the dashboard and withdraw the center part , wipe it 100 % clean using lint free rags , then set your pot (or tube I guess) of grease on the floormat on the clean newspaper you've all ready spread out , slather globs of grease on the center cable and begin working it back into the housing , adding grease as you go , too much trumps to little here and as it globs up around the mouth of the cable , recover it and slather on the cable again... work slowly and carefully ,when it stops sliding in give it a little twist to ensure the square tip is fully seated into the drive gear , wipe off the excess then clean your hands then re-attach the cable to the back of the speedo .

    Once in a while the extending tip of the center part is too long so nipping off 1/8" will stop the needle's hunting .

    Now you can ever so carefully remove the plastic garbage bag and marvel at how nasty your clothes would have been for the next several months as the graphite worked it's way out of the seams and pores & onto your new pants thence onto the nearest white thing or SWMBO's car seats etc.....

    If you're anywhere near some old junked bigger trucks with two speed rear ends , go look up and down the cable until you find a joint in it with a funny little box , carefully remove the box and the cable , give this a try on your too slow cable as it's a reduction box for just the purpose you're having ~ the speedo reading differently when you change the rear end , Brand 'F' used to have nifty vacuum controled ones in the late 1940's and early 1950's....

    I hope this helped .
     
  9. mel 55_1

    mel 55_1 Member

    Joined:
    Apr 1, 2004
    Messages:
    98
    Location:
    England
    Graphite it is then. And thanks for the garbage bag advice Nate, I can never do anything, even just taking the lid off the can, without getting that stuff everywhere.
     
  10. ccharr

    ccharr Member

    Joined:
    Jun 7, 2006
    Messages:
    2,175
    Location:
    Simi Valley, Ca. , La Paz County, Az.
    Bill What brand and model is your gps device?
    Thanks,
    Charles
     
  11. 51 HHR

    51 HHR Member

    Joined:
    Apr 26, 2008
    Messages:
    218
    Location:
    New Egypt New Jersey
    gps device

    I have a Garmin Nuvi 265
    it incorporates traffic and a blue tooth which on a scale from 1-5 i give those options a 3 they work but ahhh.
     
  12. Bill Hanlon

    Bill Hanlon Member

    Joined:
    Jun 4, 2002
    Messages:
    2,491
    Location:
    Klein TX
    Bill:
    Your original comment said that
    30 MPH indicated = 50 actual
    40 MPH indicated = 60 actual
    This does not sound like incorrect speedo gearing to me. More likely a problem in the speedo head.
     
  13. vwnate1

    vwnate1 Member

    Joined:
    Jan 1, 2000
    Messages:
    11,139
    Location:
    AMERICA !
    Garbage Bag Drop Cloth

    It works ! don't even *think* about topping up the brake fluid on a Moto until the bag is taped to the fuel tank..... :eek:
     
  14. Wolf

    Wolf Member

    Joined:
    Apr 20, 2008
    Messages:
    888
    Location:
    Kansas
    Thanks guys. My next trip to the auto parts store I will look into some graphite grease.
     
  15. aggiejon

    aggiejon Member

    Joined:
    Jul 24, 2010
    Messages:
    20
    Location:
    Central Texas
    You can get powdered graphite at your local John Deere dealer. Comes in a container similar to baby powder.
     
  16. Wolf

    Wolf Member

    Joined:
    Apr 20, 2008
    Messages:
    888
    Location:
    Kansas
    had a chance to check mine with our GPS. Right on!!! The bounce has calmed down, still every now and then, but not like it was. But I figured it was right on, as i checked it with the mile lines and my ODO was right on as well.
     
  17. Pontiac1976

    Pontiac1976 Member

    Joined:
    Aug 21, 2006
    Messages:
    482
    Location:
    Ontario, Canada
    Bill might be right, but if the tires size has been up grade to bigger then stock then that could be the differens.
    good luck :)
     
  18. gypsy truck

    gypsy truck Member

    Joined:
    Oct 2, 2007
    Messages:
    318
    Location:
    Florida / Illinois
    mine reads perfectly

    my speedo is still just reading ZERO and so does my gps. :(

    maybe if it ever gets out of the garage and on the road, i will have something to complain about....good thing i got those bigger tires.....
     
  19. brit 50

    brit 50 Member

    Joined:
    Dec 6, 2005
    Messages:
    1,202
    Location:
    Essex England, the motherland
    Earths rotation

    Dont forget to factor in the earths rotation when calculating road speed, if you are going with the rotation your speed may on the face of things be slower but add to this the earths rotation and it will make a big difference. Against the rotation and you will think your hammering along when in fact if you allow for the rotation, you are getting nowhere fast.

    This is only east to west and vise versa, not north south of course:cool:
     
  20. jinaeve

    jinaeve Member

    Joined:
    Jan 4, 2011
    Messages:
    25
    Location:
    Murphy, TX
    I know I'm a bit late to this discussion but didn't see this guy referenced here but it may be of some use to some of you looking to improve the accuracy of your speedo.

    This guy requests that you determine the actual speed by using things like GPS, radar boxes on the side of the road or remembering what your speedo read and what the officer kindly informed you were actually driving :)

    In either case, having a baseline of what your vehicle is traveling vs what your speedo reads - he takes that ratio and conforms this adapter to make up the difference. You then attach the adapter to your trannie and your cable to the adapter and walla - you're set with an accurate speedo.

    http://www.speedcorrect.com/

    Hope this helps.
     

Share This Page