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150 vs 120 mph speedo swap, recalibrate? #994236
05/17/11 01:52 PM
05/17/11 01:52 PM
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Rancho Cucamonga,Ca
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392charger Offline OP
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392charger  Offline OP
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The speedo in my 69 GTX has never worked so last night we swapped out the speedo from a coronet. Actually we just used the whole instrument cluster from the coronet and installed the GTX's 150 lens onto it. Since the mph "spread" is different between a 120 and a 150 lens, I assume the speedo is going to be off now. How do you correct that? Is it a special speedo itself or do you just change the gear in the tail shaft? Hope this makes sense what I'm asking and thanks for the help.

Re: 150 vs 120 mph speedo swap, recalibrate? [Re: 392charger] #994237
05/17/11 01:58 PM
05/17/11 01:58 PM
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JohnRR Offline
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It's a different speedo and the calibration is built into the speedo, the gear in the trans doesn't care what speedo is connected to it. there isn't the same number of has mark on the metal part so I'm not sure how you could recal it ?

Re: 150 vs 120 mph speedo swap, recalibrate? [Re: JohnRR] #994238
05/17/11 04:48 PM
05/17/11 04:48 PM
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392charger Offline OP
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Bummer Hey thanks JohnRR for the info though.

Re: 150 vs 120 mph speedo swap, recalibrate? [Re: 392charger] #994239
05/18/11 02:06 AM
05/18/11 02:06 AM
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Fresno, CA
Jim_Lusk Offline
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No reason you can't make the adjustment with a different speedo gear in the trans. You need it to read "slower" than it will read with the gear that is in it. Start with a 25% increase in teeth, if you can find one.

Re: 150 vs 120 mph speedo swap, recalibrate? [Re: Jim_Lusk] #994240
05/18/11 11:00 AM
05/18/11 11:00 AM
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JohnRR Offline
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Quote:

No reason you can't make the adjustment with a different speedo gear in the trans. You need it to read "slower" than it will read with the gear that is in it. Start with a 25% increase in teeth, if you can find one.




Jim part of the problem is the misplaced markings, I guess if he is able to ignore the misplaced hash marks and only look at the numbers, which are very jumbled together in the center of the speedo where most of daily driving is done then I guess one could experiment with different gears.

On that note maybe one of those speedo calibration shops still exists in his area that can do the fix?







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