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Old 06-14-2013, 04:18 PM   #1
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Fixing Speedometer To Match Tires

What about after you swap your tires for larger ones?
Your speedometer should not correctly read how fast you are now traveling. I'm not a speed demon. But I do want to know how fast I am going.
What do you have to do (other than rely on your GPS) to fix the TJ speedo to show the correct speed?
Is this a matter of replacing a worm gear in the tranny, or is it an electronic fix?

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Old 06-14-2013, 04:28 PM   #2
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It depends on the year. On my daughter's 98 it was replacing a gear (I think on the transfer case) On the newer TJ's I think the speedo is electric and can be recalibrated.

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Old 06-14-2013, 04:28 PM   #3
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depends on the Jeep.

my 04 (auto w/ 241J T-case) does not have a gear and needs to be digitally altered.

I believe that the 97-02 have a gear that can be changed.
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Old 06-14-2013, 04:31 PM   #4
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speedo gear for ~$40 or speedohealer box for ~$160 (box required for Rubicons and 241 transfer case)
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Old 06-14-2013, 04:46 PM   #5
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Read this thread. Once I swapped, I confirmed that I had the correct gear by using my GPS. I'm not aware of another way unless you take it to a shop.
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Old 06-14-2013, 04:56 PM   #6
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All '97 and newer TJs need only to have their speedometer gear (on the transfer case) changed to recalibrate the speedometer. It's about a 5-minute job to unsnap the old speedometer gear & snap the new speedometer gear into place.

Only the Rubicon's speedometer needs to be electronically calibrated, its 4:1 t-case does not use a speedometer gear.
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Old 06-15-2013, 10:35 AM   #7
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P.S. Here's how to figure out what speedometer gear tooth count you need & how to swap it... Changing Your Jeep Speedometer Gear
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Old 08-18-2013, 05:29 PM   #8
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The site listed above says to use 31 tooth for my 97 Sport with 33" tires and 355 gears. I looked at morris 4x4 chart and they say to use 30" tooth. Is there a big difference in the two? My tires are 33X12.5.
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Old 08-18-2013, 05:55 PM   #9
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A 31 tooth gear is the correct one to use for 3.55 and 33" tires.

The chart at Changing Your Jeep Speedometer Gear is known accurate and GPS verified.

There are inaccurate charts around, that is for sure. Quadratec has two charts floating around their website... get this, their two charts give different recommendations in a few tire & ratio combinations, only one of their charts is completely accurate.
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Old 08-18-2013, 06:14 PM   #10
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Originally Posted by Jerry Bransford View Post
A 31 tooth gear is the correct one to use for 3.55 and 33" tires.

The chart at Changing Your Jeep Speedometer Gear is known accurate and GPS verified.

There are inaccurate charts around, that is for sure. Quadratec has two charts floating around their website... get this, their two charts give different recommendations in a few tire & ratio combinations, only one of their charts is completely accurate.
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Any brands better than others or ones to stay away from?
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Old 08-18-2013, 06:30 PM   #11
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Can't recall anyone ever posting negative comments about any particular speedometer gear brands, they all seem fine.

And if your speedometer doesn't work after installing the new speedo gear, give the housing a little more of a turn so the new speedo gear can more completely engage the pinion gear inside the tcase. Different speedometer gear tooth counts have different diameters & the housing is coencentric shaped so it can move the gear further away or closer to the pinion gear inside the tcase as required.
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Old 08-18-2013, 06:51 PM   #12
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I got a question. I'm running 30" on my 00' sahara. The speedo reads 5 mph slower than actual speed. I would assume if the p.o. had larger tires on it wouldn't it read faster rather than slower? Any thoughts?
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Old 08-18-2013, 07:05 PM   #13
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I got a question. I'm running 30" on my 00' sahara. The speedo reads 5 mph slower than actual speed. I would assume if the p.o. had larger tires on it wouldn't it read faster rather than slower? Any thoughts?
Unless he never changed out the speedo gear. If youre running 30s what did it have when you bought it from the PO?
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Old 08-18-2013, 07:18 PM   #14
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That's the problem. I bought it from a small dealership. So I have no idea if the speedo was regeared or if that's just just how it is. Saving for a lift n bigger tires so ill wait til that's done before I start worrying about it. I was just curious what people had to say.
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Old 08-18-2013, 08:28 PM   #15
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That's the problem. I bought it from a small dealership. So I have no idea if the speedo was regeared or if that's just just how it is. Saving for a lift n bigger tires so ill wait til that's done before I start worrying about it. I was just curious what people had to say.
I bought mine from a huge dealership - and they didnt care enough to swap the speedo out either... Until my third or fourth return visit for repairs they should have done before they sold it.

They sold it to me with a leaking rear main seal, horrendous death wobble, wrong speedo gear, and in their own words after I pointed it out "cheap chinese knock off tires".

I wouldn't be surprised if they didnt regear it. It sounds like they didnt.
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Old 08-19-2013, 06:44 AM   #16
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Originally Posted by pi55edoff View Post
I got a question. I'm running 30" on my 00' sahara. The speedo reads 5 mph slower than actual speed. I would assume if the p.o. had larger tires on it wouldn't it read faster rather than slower? Any thoughts?
Slower at what speed? The speedometer difference will be a percentage. The faster you go, the greater the error. Yes putting on smaller tires will increase the drivetrain rpm and the speedometer will read faster.
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Old 08-22-2013, 12:27 AM   #17
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Quote:
Originally Posted by pi55edoff View Post
I got a question. I'm running 30" on my 00' sahara. The speedo reads 5 mph slower than actual speed. I would assume if the p.o. had larger tires on it wouldn't it read faster rather than slower? Any thoughts?
without knowing every detail i feel like u went from 33 to 30 tires.

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