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Old 03-17-2012, 05:47 PM   #1
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Speedometer correction

I just ordered a DPG super-ultimate lift kit and will getting new 33 inch tires once I get it installed. From everything I've been reading, there is strong suggestion that I should consider 4.88 gears in place of the stock 4.10 in the Rubicon because of the very low OD ratio in the 42RLE transmission. My question is; what are the options for speedometer correction if I change gears, or even if I don't.

I've read about Speedohealer and saw something about Superchips Flashpaq, but I can't tell if either are CARB approved here in California. Any help would be greatly appreciated. Thanks.

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Old 03-17-2012, 08:20 PM   #2
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I dont think you can reprogram your speedometer .... i think you will have to do it the old fashion way and change the speedo gear ... Quatratec has a chart that helps you choose the correct one for you tires and gears.

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Old 03-17-2012, 08:36 PM   #3
Knows a couple things...

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The Rubicon is a different beast, it does not use a speedometer gear... its speedometer is totally electronic. The dealer can reprogram it for somewhat bigger tires and I think 33" is in their ability.

OR, buy an electronic speedometer calibrator like a Superlift Truspeed or Dakota Digital which is spliced into the wiring from the sender at the t-case. Dakota Digital is at Universal Speedometer Signal Interface

Once you have one of those, you can recalibrate the speedometer to whatever tire and axle ratio you're running, as often as you want.
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Old 03-17-2012, 09:38 PM   #4
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Jerry,
Changing gears is probably going to effect the speedo more than the tire change (going from 4.10 to 4.88). If I've done my calcs right, the combo of 33's + 4.88's should result in the speedo being low by about 5 mph. Do you think the dealer could fix this with the program? Or do you think the better bet is to use one of the aftermarket devices you suggest.

I was going to go with the FlashPaq, that claims to be able to handle this and there are at least a few wesites saying its CARB approved, but when I checked the CARB EO's, the unit that supports the Jeep 4.0 isn't listed (its supposed to be EO D-330-9). It figures
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Old 03-17-2012, 10:00 PM   #5
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Eek
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Old 03-17-2012, 10:12 PM   #6
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I meant to say the speedo would read higher than actual speed by 5 mph at 70.
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Old 03-18-2012, 02:25 AM   #7
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I bought a speedo healer for my bike and hated it. i replaced it with a speedo DRD
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Old 03-18-2012, 07:23 AM   #8
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I've been running a Yellr Box for several years. It's another alternative for the Rubi.
Official home page of the Yellow Box Speedo Recalibrator

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