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The new 32" tires were on and the differentials had their new 4.56 gears installed, and the speedometer was indicating 10 MPH faster than the 55 MPH the GPS receiver said I was going. Hmmm....time to get a new speedometer gear and get things back in sync. The worst part of this was that the Jeep was rolling miles up faster than it actually traveled. Kind of throws the maintenance schedule off a bit!
I picked up the gear from the parts counter at the Jeep dealership. I had ordered it earlier in the week. Don't ask me why they don't keep a better stock on hand...maybe yours will!
After I got home, I grabbed the creeper and rolled under the TJ for a quick look.
The above picture is the speed sensor and speedometer adapter that is located on the rear of the transfer case. Since we don't have mud in Arizona (at least not very often), I only had to contend with a bit of dust. If your t-case is covered in mud, you might want to give it a good rinse first since you are going to be exposing the internals when you pull the housing.
You need to remove the electrical plug from the speed sensor. The red plastic
portion of the plug is actually a lock (trust me on this....I found out the hard way).
You need to push the tab down, from the top (see next picture).
Once the tab has been pushed into the unlock position, you can depress the small square
tab, near the end of the plug where the wires enter, and remove the connector from the
speed sensor. Next, remove the bolt that is clamping the speedometer adapter into
the transfer case. Make sure you wipe off any dirt in the area before pulling the
adapter out of the transfer case.
Grasp the speed sensor and gently pull the adapter out of the transfer case. There is an o-ring that provides the seal to prevent anything from getting into the transfer case. The o-ring should remain on the speedometer adapter. You can see the speedometer gear (red) which is what you are going to change. The number of teeth are stamped on the gear (at least it was on mine).
After you have wiped the ATF from the adapter and gear, firmly pull the gear out of the adapter housing. The factory service manual does not say how this is done, they just say remove it (of course, they also said to remove the electrical connector from the speed sensor....lock, lock, what lock?). I finally ended up pulling firmly on the red gear and it popped out of the end of the speedometer adapter.
The above picture shows the speed sensor removed from the speedometer adapter. This is not necessary for you to do. I did it thinking that was how the gear came off (hey, the factory service manuals aren't perfect). There is no need for you to open this. I thought I would show this picture so you had an idea what it looked like, just in case you were wondering what that other small bolt was holding together!
Coat the shaft of the new gear with ATF. Firmly push the new gear into the end of the speedometer adapter. Be sure you know the number of teeth on your new gear. If it is not marked, count the teeth now. Note that there are index markings on the speedometer adapter body.
Install the speedometer adapter into the transfer case. Rotate the adapter until the required range number of your gear is pointing down to the ground in the 6 o'clock position. Reinstall and make sure the speedometer adapter clamp is in the notches of the adapter and then replace the retaining bolt. Tighten the clamp bolt to 90-110 INCH POUNDS torque. Connect the electrical connector to the speed sensor.
If you notice that your speedo assembly is leaking ATF (after a day or
two), you probably tore the o-ring on the speedometer adapter. This is a
very common occurrence. Be sure to generously lube the o-ring area with
ATF when you are inserting it into the t-case to help ensure it does not tear
again. You can obtain a new one from the dealership or from such places as
ACE Hardware, an auto parts store, etc. Just find a place that has an
o-ring selection. Here are the specs for it:
Outside Diameter = 1 7/8-inch or 44mm
Inside Diameter = 1-9/16-inch or 40mm
Wall Thickness = 3/32-inch or 2mm
That is it. Take your Jeep out on the road and see how your speedometer does. Hopefully you got the right gear and your speedometer is accurate again.