how to change speedo calibration on 99 wrangler - JeepForum.com
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post #1 of 14 Old 07-22-2010, 11:59 AM Thread Starter
dmw319
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how to change speedo calibration on 99 wrangler

I did a search and read a few posts, none of which answered my question, so here it is..

My 99 wrangler has 33" bfgs and a 3.5" body/suspension lift. stock gears and axles, etc (i think, just bought the car). While driving next to my wifes car, the speedo reads about 10mph off (driving at about 65 mph on highway the speedo read only 55). What is the best way to fix this problem? Any write-ups or links would be very helpful. thanks!

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post #2 of 14 Old 07-22-2010, 12:01 PM
Jerry Bransford
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You'll need to know your axle ratio and once you figure that out, go to Changing Your Jeep Speedometer Gear and click on the chart. With your axle ratio and tire size, the chart will tell you what speedometer gear tooth count to use to recalibrate your speedometer. That webpage will show you how to swap the speedometer gear which can be done in 5-10 minutes with nothing more than a 1/2" wrench.

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post #3 of 14 Old 07-22-2010, 12:02 PM
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Either a new speedo gear or a digital speedo box. Fairly common thing because the final drive ratio is now off.

Edit: Jerry posted while I did. He explained the speedo gear route. With the electronic box (like the dakota digital) you can keep changing it.

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post #4 of 14 Old 07-22-2010, 12:02 PM
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'98 TJ Speedometer Gear
TJ speedo gear chart : Raingler.com

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post #5 of 14 Old 07-22-2010, 12:04 PM Thread Starter
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how do i determine the axle ratio?
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post #6 of 14 Old 07-22-2010, 12:11 PM
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There are a few ways. If you are positive it is stock, you can read the little metal tag on the diff. The other way is to jack up the rear end and count how many rotations the drive shaft makes for every 1 rotation the tire makes. The tag on the diff should be correct though. It should look like this:



Edit: this axle is 4.63 gear ratio as indicated by 4_63 written on the left side of the tag.

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post #7 of 14 Old 07-22-2010, 12:17 PM Thread Starter
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thanks ill check that if i can still read it haha.
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post #8 of 14 Old 07-22-2010, 01:03 PM
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Quote:
Originally Posted by dmw319 View Post
While driving next to my wifes car, the speedo reads about 10mph off (driving at about 65 mph on highway the speedo read only 55). What is the best way to fix this problem? Any write-ups or links would be very helpful. thanks!
You need a speedometer gear with 3 less teeth, 1 tooth = 3 mph...

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post #9 of 14 Old 07-22-2010, 01:05 PM Thread Starter
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best place to buy the speedo gears?

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post #10 of 14 Old 07-22-2010, 09:13 PM Thread Starter
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thanks guys! ordering one from quadratec now. i had 4.11 gears and 33" tires, so i got a 36.

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Last edited by dmw319; 07-29-2010 at 11:22 AM.
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post #11 of 14 Old 07-29-2010, 11:23 AM Thread Starter
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BUMP. I put the new speedo gear in last night and the speedometer read EXACTLY correct with the speed on my GPS. Thanks!

Here is the weird thing.. there was a 41 in there when I replaced it with a 36. Strange...?

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post #12 of 14 Old 08-02-2010, 10:41 PM
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Excellent info, I have been working with a local shop for a month on this very issue. After reading the instructions I just ordered the correct gear and will install myself.

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post #13 of 14 Old 12-05-2017, 08:43 AM
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Resurrecting old thread because TJ knowledge is timeless. Is there a real need to change speedometer gearing if you have a manual transmission? I am running 33s and 10% seems accurate as the delta from actual speed and acceptable IF I am not overlooking other consequences.
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post #14 of 14 Old 12-05-2017, 01:58 PM
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Originally Posted by eddiefast View Post
Resurrecting old thread because TJ knowledge is timeless. Is there a real need to change speedometer gearing if you have a manual transmission? I am running 33s and 10% seems accurate as the delta from actual speed and acceptable IF I am not overlooking other consequences.
No need to change it if you don't mind the speedometer and odometer being off.
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