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Teckelhut

Speedometer issues

Question

I have an all original (except the engine which was upgraded to a 350) 1984 Trans Am (photo in icon). I am the second owner. Purchased this car last month.



The speedometer is accurate until it hits 50 MPH then everything starts getting faster (for lack of a better word) by 5 miles. If it says 60 you are doing 55, 65 = 60, 70 = 65, etc. How can we fix that?



Thanks!




Sussie


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4 answers to this question

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Hmm. Ive never seen a spedo get inaccurate in a nonlinear manner like that. Electronic spedo?

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I have two initial suspensions. First of all, are the tires the same size as the original tires? I believe 14", 15" and even 16" wheels were available that year so I am not sure what size tire is correct for your car. You should have a tag on the drivers door. I am wondering if you have incorrect tire sizes, which will impact your speedometer's reading.



Second suspect is the wrong speed calibration gear in the transmission. If the engine was changed, it is possible that the transmission might have been changed from another donor car as well, with the wrong calibration gear.



You can solve your problem by taking your car to a competent shop (preferably one that has a rolling dyno) that can determine the proper calibration gear you need and install it between the transmission and the speedometer cable. Check with your local transmission shops to see if they do this sort of work or recommend someone who does.

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Im leaning towards the second possibility Frosty. Wrong tire size would make it inaccurate in a linear manner. The Phoenix does this on the 14s instead of 15s. OP says its a nonlinear inaccuracy, most likely in the transmission especially since the engine was swapped.

Sent from my SAMSUNG-SGH-I547 using Tapatalk

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Any news?

Sent from my SAMSUNG-SGH-I547 using Tapatalk

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