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Thread: Auto to manual speedo reading incorrect

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    Auto to manual speedo reading incorrect

    Hi I have just purchased my s15. Upon driving home I found the speedo doesn't read properly. As said in the title the car has had a auto to 5 speed manual conversion. Any one had this problem?
    Cheers Derek

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    East Anglia Area Rep Slip_n_slide's Avatar
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    It will be to do with your diff ratio. Autos have a shorter diff ratio than a manual so the gearbox speed sensor won't read the correct road speed. My 14 has had a manual conversion and bigger wheels put on so 10 mph on the speedo is actually 9 on the road. 10% out may not be a lot but i agree, 78mph on the speedo being about 70 on the road is a tad annoying.

    On the plus side, you're never going to b going over the speed limit if you follow your speedo and an auto diff with a manual box gives better acceleration.

    If you want to fix it a manual diff will help but the car won't accellerate as fast. If you do decide to do this, check the diff ratios for an s15 manual diff against the 5 and 6 speed box diffs to make sure they're the same.

    Chances are the 5 speed box in an s15 is the same as a 5 speed in a 14 so the manual diffs should be the same. Sure someone will be able to clarify.

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    Guest v17nyb's Avatar
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    Easier fix is to change the speed sensor on the manual box for the auto one

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    East Anglia Area Rep Slip_n_slide's Avatar
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    Lol, didn't know they were interchangeable.

    Don't tell me it's just a case of unscrewing and sliding the new one in?

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    Cheers guys. Mines is reading at say roughly 30kmh is 40mph. Will try a sensor. Cheers guys.

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    Guest jj205mi16's Avatar
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    s15 doesnt use a speed sensor on the box though? it uses wheel speed from the abs rings as far as im aware.

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    Guest v17nyb's Avatar
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    Correct! My baad
    I'll shut up and just stick to the 14 technical thread

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    NE and Merch Rep type Vigilant teSte's Avatar
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    Quote Originally Posted by jj205mi16 View Post
    s15 doesnt use a speed sensor on the box though? it uses wheel speed from the abs rings as far as im aware.
    Well that is gonna make our S14s new running gear interesting in the speedo dept

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