Speedo Off by "a lot"

[Deleted User]
[Deleted User]
edited November -1 in HUDSON
During our trip to get the Pacemaker to our new house, my chase vehicle told me I was about 5-7 miles under what my speedo was telling me.



At 60 mph I was told I was only going 55.



At 65 (downhill), I was told I was going 61.



At 55, I was told I was going 48.



What do I need to do to help fix this?



Tires are Kelly/Goodyear reproductions of the standard tire for the Pacemaker.

Comments

  • Aaron D. IL
    Aaron D. IL Senior Contributor
    You can actually lubricate the speedo guage and that might do the trick. Most people don't know it but if you take the guage out there's what looks like a rivet on the back. you put some drops of air tool oil in it and it lubricates the bearing inside the speedo (ditto if your guage is making noise). If the rivet is full of dirt you can pop it out. Below it is a felt wick and drop some drops of air tool oil or machine oil on that.



    You can also take out the cable itself and lubricate that with graphite. As cleanly as you can anyways. If that doesn't improve guage accuracy well it is possible that someone put in a wrong speedo gear although you can argue how accurate they ever were. Doing 5 mph over won't get you a ticket in most states.
  • [Deleted User]
    [Deleted User]
    I too have this problem with my '50 Pacemaker Deluxe. It has overdrive with Supermatic Drive. When my speedometer is indicating 70 mph, I'm really doing about 62. I just learned to live with it. However, Aaron's suggestion of lubricating the speedometer gauge and cable may be worth pursuing to improve mph accuracy.
  • [Deleted User]
    [Deleted User]
    edited November 2013
    And, you are assuming that your pace vehicle's speedometer was correct... (?)...

    [/quote]Based on the "Watch Your Speed" radar signs we passed, Yes.
  • Aaron D. IL
    Aaron D. IL Senior Contributor
    Also ...and this is a shot in the dark...tire size might have an effect?
  • [Deleted User]
    [Deleted User]
    Aaron D. IL wrote:
    Also ...and this is a shot in the dark...tire size might have an effect?
    I double checked.....but the new ones are the same Kelly/Goodyear reproduction size as listed in the manual.
  • Lee ODell
    Lee ODell Senior Contributor
    A speedometer shop can add a speed correction adaptor between the trans and speedo cable to take care of the problem if the suggestions mentioned do not cure the problem. I have used this method with good results.



    I think speedometer errors were common back then. My 40 Ply had the same problem. Even my 69 AMX still has this problem. 15% error. Rather than speeding money on another adaptor I asked for a list of what the speedometer says at 35, 45, 55, 65, 70, MPH and drive accordingly.



    Lee
  • [Deleted User]
    [Deleted User]
    On my 51 I pulled the cable off. Pulled the core cable out of the sheath and cleaned both. The sheath was full of crap. Soaked it then blew it out. Graphite grease on the cable and back in the sheath. Sure made it run quite. It was noisy before and bounced a little. I also oiled the speedo as described above.
  • dave s
    dave s Senior Contributor, Moderator
    Are you sure the speedometer has proper number of teeth for your ratio rear end and tire size? One less tooth should take care of problem. You can find correct number of teeth needed in Hudson parts book.
  • 53jetman
    53jetman Senior Contributor
    Aaron D. IL wrote:



    You can also take out the cable itself and lubricate that with graphite. As cleanly as you can anyways. If that doesn't improve guage accuracy well it is possible that someone put in a wrong speedo gear although you can argue how accurate they ever were. Doing 5 mph over won't get you a ticket in most states.



    I have found it better to lube the cable by removing it from the casing, and cleaning - then soaking in automatic trans fluid. ATF does not cake over time, and continues to lube the cable
  • [Deleted User]
    [Deleted User]
    dave s wrote:
    Are you sure the speedometer has proper number of teeth for your ratio rear end and tire size? One less tooth should take care of problem. You can find correct number of teeth needed in Hudson parts book.
    This is the OEM, factory installed cable. I will be taking it out and cleaning it plus lubing the speedo.
  • SuperDave
    SuperDave Senior Contributor
    As Lee mentioned a speedometer shop can make a gear reduction box to correct errors. Does anyone have first hand,current experience with any of these shops? I have an error that cannot be corrected by changing drive gears(They are not available) And would like to have a box made, but am leary of some of the claims. I would like to deal with someone with "history"..
  • 48super6
    48super6 Senior Contributor
    I agree that I think it was common for the speedometers to be off by a bit back then. I always thought it was to keep the number of speedometer gear sets to a minimum, given the different rear end ratios, optional tire sizes, and variances in tire diameters between manufacturers for the same size tires. If you look at a lot of the magazine road tests up though the 1970s, you'll see that it was quite common for the speedometers to be off. I noticed that it seemed that most American cars ran faster than indicated (opposite of what you are experiencing) and foreign cars ran slower. If they ran slower than indicated, people thought they were faster and got better gas mileage than they really did, and it could be as much as 15% or so. I know early VW rabbits were notorious for this, as were other makes. The cynic in me thinks it may have been on purpose http://classicar.com/forums/images/smilies/eek.gif.



    You might also want to check the rear end gearing to see if you have the correct ratio or if someone swapped it out at some point. Depending on what the ratios are, you'd probably see an even greater discrepancy- it also would be a percentage relative to the speed, not a constant 5-7 mph.
  • [Deleted User]
    [Deleted User]
    48super6 wrote:
    ...snipped...You might also want to check the rear end gearing to see if you have the correct ratio or if someone swapped it out at some point. Depending on what the ratios are, you'd probably see an even greater discrepancy- it also would be a percentage relative to the speed, not a constant 5-7 mph.
    This car has remained in the original owner's family and those still alive know that the rear diff is the OEM factory unit.
  • Lee ODell
    Lee ODell Senior Contributor
    SuperDave, you might contact your state Highway Patrol for a good speedometer shop.



    I'm not familiar with Florida but for those living in the Los Angeles, Ca area you might give North Hollywood Speedometer, North Hollywood, Ca a try. I have used them for over 40 years when I needed their help.



    Lee
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