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If you've had your Jeep long enough to change the wheels and tires (usually one of the first mods new owners will do), you also know that your speedometer will not be indicating the correct speed after your new tires are under your ride. As the TJ model grows older and older, finding the correct gear to calibrate your speedometer becomes more difficult. Add to that the plethora of axle gear ratios and tire sizes (not all tires sizes measure the same from brand to brand).....and you can end up with a combination that is darn hard to work with.
So.....why not just do it the easy way? Leave the speedometer gear
right where it is in the transfer case and install the SpeedoHealer speedo
calibrator by HealTech Electronics. You can get one from
Motorsports. They have configurations to fit a variety of
Jeeps including your TJ. Let's take a look at the what it takes to get the
TJ converted over to an electronic speedometer calibration module.
The SpeedoHealer comes as a two part kit. Everything you
need....everything....is included in the package. The TJ package includes
the SpeedoHealer itself and an install harness that provides the necessary
connectors to integrate the tiny computer into your TJ's wiring harness.
The SpeedoHealer's install harness comes with zip ties and
instructions to guide you, step by step, through the very simple installation
process.....and it is indeed very simple. If you think you are one of
those folks that are all thumbs when it comes to such things, relax.....you will
do fine. According to a comment in Blue Monkey's install docs, one of the
staff's 15 yr old daughter completed the install in just 5 minutes. So,
let's take a look at what is involved with getting the SpeedoHealer installed in
Here is a pic of my NP231 transfer case. The speedometer sensor sports a red circle in the above photo. The speedo sensor is a gear driven device that converts mechanical rotation into electronic pulses. These pulses are routed to the engine computer where it counts them and then sends a speedometer signal to the instrument cluster to indicate how fast you are going. You can see why changing the axle's gear ratio and/or the tire size will change the vehicle's true speed while the speedo sensor generate the same electronic pulses.
So.....this is where the SpeedoHealer takes over and corrects those signal pulses going to the engine computer. In doing so, the TJ's actual speed and the electronic speedo pulses are once again in sync and your speedometer will be indicating the correct speed.
The first step, once you have the parking brake set and/or a wheel chocked in
place, is to unplug the factory connector from the speedo sensor. There is
a red locking tab on the connector that must be pushed to unlock the connector
so it can be removed from the sensor housing. The
yellow arrow is pointing at the locking tab (red piece
Push the red tab in a downward
direction, from the top. It may be a little stubborn but it will move into
the unlocked position with some good finger pressure.