After lifting our Jeeps and installing larger tires, the next job we have is to recalibrate the speedometer. Our stock speedo gear is designed to be used with original size tires. If we do not change this simple plastic gear after changing tire sizes we are going to throw off our speedometer, trip computer, odometer, etc. Fear not! We are $20 and 10 minutes away from solving the calibration problem.

Your local Jeep dealership will be able to order the necessary part for you and it should cost around $20. The install should cost you nothing since it requires one hand tool and about 10 minutes of your time.

Here is a list of common gear/tire combinations that should help you find what gear is right for you:

Example: SG34 = speedo gear with 34 teeth

Updated 03DEC99:

In order to figure out if your t-case requires the short (2.2") or the long (4.3") shaft gear we need to look at the connection. If you have the newer electronic type of connection at the t-case where the speedo gear is you will have the short shaft (1993-2000). If you have a cable type connection at the t-case where your speedo gear is you will have the long shaft (1987-1993). You may want to remove and measure it just to make sure.

Note: The above are Chrysler part numbers and can be ordered directly from your dealer.

First step is to go to the driver's side of your Jeep and crawl under there. You will easily locate the rear driveshaft that connects the transfer case to the rear axle. Now the gear that we will be changing is in the transfer case. You will see a wire loom that plugs into the rear upper part of the transfer case - this wire loom feeds the vehicles computer the rotational speed of the output shaft and that, along with other information, is used to compute your speed.

There is only bolt that we need to remove along with the retaining tab that holds the connection in place.

Now pay attention to how the plug is oriented prior to removing it - you may wish to mark it right now for proper positioning when re-installing. This is not critical for the gears or other internal parts - it will make it easier to re-install the mounting tab and screw. Now wiggle the plug nice and easy while pulling and the whole assembly should pop right out.

The stock (orange in this case) speedo gear can be removed with a firm tug.

The new gear will be installed with the metal end first. Make sure the part is seated all the way prior to re-installation. A solid push should be all that is necessary to install your new gear. Now we must rotate the speedometer adapter so the different size (new) gear will engage properly.

You will notice the index number location markings on the adapter. Find which index your new speedo gear falls into and rotate the adapter untill that index is in the six-o'clock position. The rotation of the adapter is a cam type of action and will bring the internal gears into contact. The rest of the installation is just the reverse order of the steps that we have already taken. Now you are done and your speedo is right on the mark.

Note: On some early transfer cases (ex. NP242) the index number location markings are actually engraved around the speedometer adapter hole on the transfer case, and not the adapter itself, which just has an arrow to be aligned with one of the marks.

You may wish to verify that you have made the correct adjustment. This is easily accomplished at the highway. Find a mile marker (they are spaced one mile apart) while traveling at 60 MPH and time the distance between mile markers. At 60 MPH you are traveling one mile per minute so you should be right at 60 seconds between mile markers. Another option is to use a GPS (Global Positioning System) to compute or speed for us. Handheld versions cost between $100-$200 and Delorme even has one that will plug right into your laptop computer!

Note: This chart only works for the newer (post 1987) transfer cases NP/NVG231, NP/NVG 242, and NP/NVG249 - not the NP207 or NP229.