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Thread: Speedo Calibration

  1. #1

    Default Speedo Calibration

    I replaced my instrument cluster with another cluster and put a new speedo cable in that I bought from Ebay. While driving today it "felt" like I was going slower than what the speedo was reading.(speedo read 80 km and I "felt" like i was going no more than 50km) So my question is are there differences in clusters where they cant be interchangeable without modification? or Is it possible for the cable to read faster than it is. Keep in mind that I did change the speedo gear in the transmission last year, but I used the exact same tooth count (19) If anyone has any idea let me know.

  2. #2
    Wagon Addicted Tiggie's Avatar
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    Instrument clusters are delicate things that don't really like going through the postal system. I'd wager the calibration of one or both of them are off. They should be the same. The speedo cable will have no effect. The gear will change things, but it sounds like you ran the newer gear with both clusters which would mean that's not the problem either.

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  3. #3

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    I got the second cluster because of the circuit board, it curled over and kept blowing the fuse for the backlight display.

  4. #4

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    and the cluster i removed from the wreckers myself, only the cable i bought through ebay.

  5. #5
    I'm an air-conditioned gypsy gadget73's Avatar
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    got a smartphone? Get you a speedometer app and see what its actually doing.

    The clusters are all the same. Off the top of my head I forget the number, but there is some RPM of the cable that equals 60 mph, and thats true for all the speedos. The cable is also just a cable. The gear is what determines the calibration. The speedo itself can be damaged internally and cause it to read funny but you wouldn't have multiples reading off by the same amount. That would be the speedo gear.

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  6. #6
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    I had the same problem with a bunch of mine. Seemed like each one was different.
    I was able to locate one of those speed radar trailers that warn drivers of their speed. At least it was a gauge as to how far off the speedo was. I finally replaced it with a nos. Those circuit boards sheets are a replaceable item. Just need part number. I have seen one recently.
    Best thing is to take it to a speedometer shop.

  7. #7
    Road Warrior Kodachrome Wolf's Avatar
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    I never found the 85 MPH units to be particularly accurate, whether cable or electrically driven. I've used both between my cars, and the error margin increased past 55 MPH it seemed. Using the '90-'94 style in the '97, 78 MPH actual read as 85+, but it read fine at 60 and under. The '87 was similar, and was true to speed at 55 MPH, but beyond that, it got way off. I think 75 MPH read 85 MPH. I did check odometer mileage vs. time, and found that to be accurate, just an over-reporting of speed at the head.

    Now the police units I've used have not had the margin of error issue with higher speed. The unit in the '87 is usually within about +/-1 and the unit in the '97 is roughly fast by 3 MPH, but that's just thanks to me not putting the needle on square.

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    GMN Regular DerekTheGreat's Avatar
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    You talking about Ford/Mercury stuff? The speedo's on our Town Cars are dead nuts accurate...
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  9. #9

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    This morning I took the speedo head out of my original cluster that came with the car and swapped it onto the unit I got from the auto wreckers. I took it for a drive and it seems to read a lot better than yesterday. I might try that speedometer app and see just how accurate it is.

  10. #10
    Beater gonna beat sly's Avatar
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    Sometimes the lubrication in the speedo mechanism gets cruddy. A little WD40 followed with some 3-in-1 oil or some other lube that will have some stick-to-it properties but isn't real thick seems to work pretty good.

    If digital cluster, sometimes just reseating everything to clean off the contacts sorts out all manner of stuff.

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  11. #11
    The Brown Blob 87gtVIC's Avatar
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    Quote Originally Posted by 1985crownvicltd85 View Post
    This morning I took the speedo head out of my original cluster that came with the car and swapped it onto the unit I got from the auto wreckers. I took it for a drive and it seems to read a lot better than yesterday. I might try that speedometer app and see just how accurate it is.
    That works too. I was going to suggest just swapped the good known printed circuit onto your original cluster.
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  12. #12
    P31 Pursuit Car Brown_Muscle's Avatar
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    There's no adjustment in there for speeds? I figured at least with the police clusters there would be a little "slower/faster" lever to adjust it, like in a clock.
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  13. #13
    I'm an air-conditioned gypsy gadget73's Avatar
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    I think they bend the tabs on the magnetic coupler, or maybe its a spring tension thing, bending the anchor point to adjust. Its not an adjustment clearly and obviously marked "calibration" though. Prob one of those things where if you know what you are looking at its cake, but I don't know what I'm looking at in there. Its got a thing that spins and the needle is connected to a C shaped thing that sits over the spinny part but beyond that its voodoo.

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    91 Lincoln Mark VII LSC SE, triple black (Timewarp) - poly front bushings, KYB struts and shocks, Holley SystemMax1 lower intake, SilverFox AOD valve body,

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    Quote Originally Posted by phayzer5 View Post
    I drive a Lincoln. I can't be bothered to shift like the peasants and rabble rousers

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