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Discussion Starter #1
OK, I have had a speedcal from Dallas mustang for several years, and had no problems with it. I swapped my 4.10's (open diff) with 3.73's (track lok). This was performed by my local ford dealership. Now, my speedo reads approx 10mph too fast @ 70mph. I have contacted Dallas mustang, and they gave me a new dip switch setup, and its still reading off. Now, I'm wondering if there's something awry in the diff, or possibly a sensor. Any input would be appreciated. ('96 T-bird, 4.6L)
 

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1997 Thunderbird 4.6, 1998 Mark VIII LSC
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You really don't need the speedcal for 3.73s. The purple 21 tooth speedo gear works fine. I'd put a new speedo gear in and take the speedcal out of the equation and see where that takes you.
 

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Discussion Starter #3
That might get me pretty close, but I'm also running 255/45r17's, so it would still be off a bit. (not much, I know, but just enough to piss me off.)
 

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1997 Thunderbird 4.6, 1998 Mark VIII LSC
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I'm running the same size tires; my speed is off by about 2%. If I'm going 70 according to the speedo, I'm actually going roughly 68.
 

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Discussion Starter #5
well, that's not too bad off. guess I'll give it a shot and see what happens. Thanks.
 

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Easy fix, check the Electronics area of the forum and look at my writeup on the Speedcal. For your initial PPM use 8000 to eliminate the 2% of error.
 

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Discussion Starter #7
Ripped out the speedcal, installed purple speedo gear, problem solved. Thanks guys!
 

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want to sell speedcal cheap? pm me.

:)
 
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