How to recalibrate your speedometer after changing tire sizes or gears

changed my speedo gear yesterday, one of the easiest things i have done to my tj so far, GPS speed now matches speed coming from ECU.
 
I may have missed it somewhere, but...
I have the '04 TJ unlimited(LJ) and was told to buy a programmer to make the swap, instead of the gear.
Will that work? I may change from the factory gear to a 4.56 or a 3.73, not sure which. While this is a bit in the distant future, what is the best (or only) option for me?


The old guy
 
I may have missed it somewhere, but...
I have the '04 TJ unlimited(LJ) and was told to buy a programmer to make the swap, instead of the gear.
Will that work? I may change from the factory gear to a 4.56 or a 3.73, not sure which. While this is a bit in the distant future, what is the best (or only) option for me?


The old guy

No. You don't need a programmer, you just need a new speedo gear which is super easy. The programmer is only necessary if you have a Rubicon model with the NP241OR transfer case.
 
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No. You don't need a programmer, you just need a new speedo gear which is super easy. The programmer is only necessary if you have a Rubicon model with the NP241OR transfer case.

Thanks! I did get the programmer, just to change the tune from factory to "low octane gasoline". I cleared my codes, shot in the new tune and have not had the catalyst codes come up in three tanks of fuel. How long that will last, I don't know.
The speedo gear is next on the list. Just changed the cooling system to Griffin and FlowKool. The new thermostat came today, that gets swapped tomorrow.
Thanks for the help!


The old guy
 
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Glad you got it figured out!

I am guessing that the altitude change from the mountains of N. GA and here was enough to mess with the usual mixture. Other than that, no clue. I'm going to get the new gear soon, I hate driving by GPS speed, plus the rain and no top + electronics..... One the magic smoke comes out, it won't go back in......lol. Oops


The old guy
 
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Unless some teeth are broken on the speedo gear I can't see how this would help if it's "all over the place" a wheel change or gear change would make it off with some level of consistency be it by a small amount or large amount.
 
If you have a 97-06 Wrangler TJ and recently went to bigger tires, you'll probably notice that your speedometer is off. This is an easy fix by purchasing the correct gear for your tire size and ring and pinion.

NOTE: This will not work on 03-06 Rubicon models. See the bottom of this post for more details on what to do if you have a Rubicon.

Here's a chart to help you determine the correct speedometer gear:

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The speedo gear swap/change takes a mere 5 minutes and only one wrench. This is an easy job that anyone can do.

Item's needed:
  • 1/2'' wrench (socket works too).
  • Some paper towels or rag. (you will drip a bit of ATF)
  • Correct speedo gear for your tire size/axle gear ratio.
  • New O-ring for the drive housing. (for $3 at the dealer, change it for cheap insurance)

View attachment 103

Once you have everything ready locate the Speedo Gear drive on the rear output shaft of the transfer case. (easily seen from the rear of the t-case skid)

View attachment 104

First action to take is to remove the electric connector. Push the lock clip out "the red tab" and press on the connector release and pull it off.

View attachment 105

Next step is to remove the 1/2'' bolt and wishbone clamp from the tail housing. Set these to the side.

View attachment 106

Once the clamp is removed you can now remove the drive housing. It will be secured tight in the tail housing..just work it back and forth until it pops out.

View attachment 107

Now it is time to remove the old gear and install the new. To remove the old just grab the gear in one hand and the drive housing in the other...pull. It pops right out with little effort.
Pull the old O-ring off of the drive housing and install the new one.

View attachment 108

Install the new speedo gear by pushing it into the drive sensor housing. Be careful not to pinch the o-ring when installing. (helps if you rub a bit of atf on the o-ring)

NOW...here is a little thing that a lot of people miss. The speedo gear is offset in the sensor housing. This is to adapt to different size gears. And there is 3 clocked position that you can install it. "But how do I do that?" Easy...look on the side of the drive sensor housing.

You will see the numbers....
26-31
32-38
39-45

View attachment 109
View attachment 110 This image has been resized. Click this bar to view the full image.
View attachment 111

Simply find where your speedo gear tooth number falls. When you install the unit into the rear tail housing point the number that your gear fall in down at the 5 o'clock position of the hole. Press the gear into the tailshaft.

View attachment 112

Install the wishbone clamp and bolt to secure the drive sensor housing. DO NOT OVER TIGHTEN the bolt. The tail housing is aluminum. Just snug it down good. Don't crank on it.
Besure you set the clamp teeth into the cuts in the drive housing.

View attachment 113

Plug the electric connector back in and you are done.

Here you will see the position that your speedo gear tooth count should be angled down. And a completed install. The installed speedo gear in this application was a 41 tooth gear...so 39-45 is down at the 5 o'clock position of the hole.

View attachment 114


NOTE: This will not work on 03-06 Rubicon models. The speedometer on these is electronically controlled and therefore you only have two options from all the research I've done:

1) Some dealers are able to re-program the ECU so that it the speedometer will accommodate for different gearing and larger tires.

2) There are several electronic speedometer calibrators out there with one popular model being the Truspeed and the Dakota Digital.
Has anyone found out what the issue is with some dealers supposedly being able to reprogram the ECU, while others have not?
 
Has anyone found out what the issue is with some dealers supposedly being able to reprogram the ECU, while others have not?

To my knowledge the dealers can't re-flash the ECU, I could be wrong though, it's worth calling your dealer.

Why would you need yours re-flashed?
 
I have an '04 LJ, I have been told that I have to have a gear change. The dealer here said nogo on a computer, as there is a cable from the Tranny to the Speedo.
 
I have an '04 LJ, I have been told that I have to have a gear change. The dealer here said nogo on a computer, as there is a cable from the Tranny to the Speedo.

Just follow the procedure explained in the first post of the thread. Changing the speedo gear is very, very, very simple.

And BTW, were they referring to a speedo gear change, or a gear change as in your ring and pinions?
 
A little help needed here. Never claimed to be the sharpest tool in the shed, but I'm not getting this.

It's jacked up, in gear, and when I spin one wheel the other spins too.

One complete wheel revolution causes three and a half drive shaft revolutions.
I would guess I have a 3.55 rear end.

I have 35 inch tires, but I don't see, on the chart, what speedo gear I would need.

According to gps my speedometer is pretty close to accurate at lower speeds, but an indicated 52 is a gps 55 mph. Higher speed = greater difference.
 
A little help needed here. Never claimed to be the sharpest tool in the shed, but I'm not getting this.

It's jacked up, in gear, and when I spin one wheel the other spins too.

One complete wheel revolution causes three and a half drive shaft revolutions.
I would guess I have a 3.55 rear end.

I have 35 inch tires, but I don't see, on the chart, what speedo gear I would need.

According to gps my speedometer is pretty close to accurate at lower speeds, but an indicated 52 is a gps 55 mph. Higher speed = greater difference.

What year, make, model (trim level) and transmission are in your TJ? That will pretty much confirm or deny whether it is indeed 3.55 gears (which it likely is).

I also updated the chart in the first post, you should have a 28 tooth gear, assuming you do indeed have 3.55 gearing.