Speedometer calibration

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DN7050

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I recently purchased a 1998 GMC Sierra 2500 (2WD, HD, long bed, extended cab, 5.7, 4L80E) which happens to be in almost new condition, no rust at all, looks new underneath and clean body too. Anyway the primary issue is the speedo reads about 15 mph high at 60 mph. I suspect the instrument cluster is not original, especially since it was originally sold in Canada but now has the US instruments. Anyway, is it possible to recalibrate the speedo and if so how?
 

1ton-o-fun

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Mine has larger (height and width) tires than stock but reads dead on, according to the 27 satellites that the speedo app on my phone says it's reading from...
 

Frank Enstein

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If the odometer is accurate just move the needle. I just did this to the wife's Astro. It read 4 MPH high at every speed. It took a few tries but it's within .5 MPH now. If the odo is off the same amount the computer can be reprogrammed.
 

kennythewelder

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The speedometer can be recallerbrated. This is done with a programer. They do sale a programmer just for that, but they a pricey. Your local chevy dealer should be able to do it for you, as can your local transmission shop. A flash tuner can also do it. Mine cost around $325 I think. Summit racing still sales it. Its a jet brand. Also any shop with a dyno that does dyno tuning can also do it. Its just a mater of reprogramming the ECM.
 

98chevy2500SS

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The speedometer can be recallerbrated. This is done with a programer. They do sale a programmer just for that, but they a pricey. Your local chevy dealer should be able to do it for you, as can your local transmission shop.
I tried calling my local Chevy dealer if they could do it, they quickly said "Nope." lol. I should call a transmission shop, didn't realize they could do it. For some reason, my 97's speedo is 5mph off, it's got the stock gear ratio and stock tires. Transmission has been rebuilt so I don't know if that effects it or not. I tried having my teacher at school reprogram my 98's speedo with HP tuners, but sadly it didn't work.
 

AK49BWL

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Something to think about: My GPS speed and my PCM speed are within 0.6mph of each other across the entire sweep (5-85)... My speedometer is around 4mph fast, also across the entire sweep. All I'm going to do is pull the needle and reposition it, because that all I feel needs to be done. If I reprogram my PCM, then my speedo MAY be closer, but my odometer and PCM won't be anymore.
 

frito-bandito

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Let me know how that works, but if you don’t, I’ll try it on mine Monday and let y’all know the results lol. I’ll first use my GPS to ensure the odometer is registering accurately. Mine reads 10mph too fast.
 

kennythewelder

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I adjusted the tire size setting with my Jet flash tuner to get my speedo to read rite. Then I swapped my cluster with a Denali cluster with the 120 MPH speedo. I had to adjust tire size again for it to read rite. The programmer is under $350.
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