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post #1 of 8 (permalink) Old 12-05-2011, 02:54 PM Thread Starter
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Speedometer reading too fast

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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post #2 of 8 (permalink) Old 12-05-2011, 03:03 PM
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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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post #3 of 8 (permalink) Old 12-05-2011, 04:52 PM Thread Starter
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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.)

-'96 T-bird, PI heads & intake, Trick flow cams, '02 GT MAF, Mustang K&N FIPK, Accufab TB, C&L Plenum, B&M shift improver, SCT chip by Lonnie, 3.73 Trac Loc, 2.5" True dual exhaust w/ SLP mufflers, 17x9 Cobra R replicas, Eibach pro kit.
-'01 Lightning, 3lb upper pulley, Superchip,K&N cold air intake. 1/4 mile [email protected]
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post #4 of 8 (permalink) Old 12-05-2011, 05:09 PM
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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.

-Brandon
97 Laser Red Thunderbird LX 162k, Stage 2 4.6L 2v N/A | 300 BHP (255 RWHP, 290 RWTQ) | 13.95 @ 97.58 | Build details | Pics at the Lorain Assembly plant
98 Black Mark VIII 160k, stock daily driver
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post #5 of 8 (permalink) Old 12-07-2011, 02:10 PM Thread Starter
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well, that's not too bad off. guess I'll give it a shot and see what happens. Thanks.

-'96 T-bird, PI heads & intake, Trick flow cams, '02 GT MAF, Mustang K&N FIPK, Accufab TB, C&L Plenum, B&M shift improver, SCT chip by Lonnie, 3.73 Trac Loc, 2.5" True dual exhaust w/ SLP mufflers, 17x9 Cobra R replicas, Eibach pro kit.
-'01 Lightning, 3lb upper pulley, Superchip,K&N cold air intake. 1/4 mile [email protected]
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post #6 of 8 (permalink) Old 12-07-2011, 02:31 PM
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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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post #7 of 8 (permalink) Old 12-20-2011, 01:19 PM Thread Starter
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Ripped out the speedcal, installed purple speedo gear, problem solved. Thanks guys!

-'96 T-bird, PI heads & intake, Trick flow cams, '02 GT MAF, Mustang K&N FIPK, Accufab TB, C&L Plenum, B&M shift improver, SCT chip by Lonnie, 3.73 Trac Loc, 2.5" True dual exhaust w/ SLP mufflers, 17x9 Cobra R replicas, Eibach pro kit.
-'01 Lightning, 3lb upper pulley, Superchip,K&N cold air intake. 1/4 mile [email protected]
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post #8 of 8 (permalink) Old 12-20-2011, 08:18 PM
No, Mr. Lemmywinks, No!!!

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want to sell speedcal cheap? pm me.


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