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Old 10-11-2011, 07:56 PM   #1
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Re-calibrating speedometer

How do I recalibrate the speedometer/odometer? Do I have to have a mechanic do it?

Thanks

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Old 10-11-2011, 08:00 PM   #2
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I know for an earlier tj with a speedo gear its a small gear on the back of the tcase. order gear and change. And im not sure bout auto speed sensor. Then odomoter I don't think can be changed by law.

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Old 10-11-2011, 08:06 PM   #3
Knows a couple things...

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The odometer is actually very easily recalibrated so long as your Jeep is not a Rubicon. It takes 5-10 minutes from start to finish to remove the old speedometer gear and snap the new one into place. It literally unsnaps and snaps back in. This also recalibrates the odometer so it reads correctly. You only need a 1/2" wrench to remove the bolt that holds the speedometer gear housing to the transfer case.

Here's how and the chart shows what speedometer tooth count to use to get your speedometer reading correctly... Changing Your Jeep Speedometer Gear

One last comment... pay close attention to where it describes how to rotate the speedometer gear housing to match the number of teeth on the new gear. BUT that is not a precise thing. You will likely need to rotate it a bit more in one direction or the other to get the new speedometer gear to mesh with the pinion gear inside the transfer case. So if the speedometer doesn't work after installing the new speedometer gear, don't worry about it, you only need to rotate the housing a bit so the two gears mesh properly with each other.
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Old 10-11-2011, 08:07 PM   #4
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I have an '05, do you know if that has the gear or auto speed sensor?

thanks
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Old 10-11-2011, 08:07 PM   #5
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Oh, thanks Jerry. I didn't see your post until I posted
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Old 12-11-2011, 10:17 PM   #6
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This is a nice link and its very descriptive but how do I know what R&P I have? I just bought a 97 TJ and was recently told (someone following me) that my speed was off by 9 MPH....as in reading 60 but traveling 69. TJ has 4 inch lift with 2007 rubicon rims 255/70/17.

Appreciate any help.
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Old 12-15-2011, 07:02 AM   #7
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If you get under the jeep the differential cover on the rear, or front for that matter, should have a tag attached to one of the bolts on the cover. That tag will have the factory gear ratio stamped on it. This assumes that the gearing hasn't been changed. That is a whole different can of worms.

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Old 12-15-2011, 08:44 AM   #8
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Worst case scenario and you don't have a tag. On whichever axle you prefer, jack that axle up so that both tires are off the ground (using jack stands, of course), mark the bottom of a tire and a convenient spot on the drive shaft (front shaft for the front axle...) and count the number of revolutions the drive shaft makes per one revolution of the tire. That should get you close enough to determe your axle ratio.
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Old 12-15-2011, 11:50 PM   #9
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Haven't done this yet (I've been in another endeavor, please see my newest post) but I wanted to address the following:

I once helped a buddy who had a GMC lifted and his mph was off. He had me ride passenger with a GPS as he popped off the speedo on the dash and placed it accordingly ... will this method work?

FYI the speed differential is not exponential. It is the same all around plus 7-8 mph.

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