How to properly change your speedo gear

[Tiffster]

By Tiffany Trott

Swapping out the speedo gear after a tire change or differential gear swap is important to the function of your Jeep. The computer depends a lot on the speedo to help it know when to do certains things (like shift on an automatic). The process is super simple and really shouldn't take you more than 5 minutes time and one hand tool.

The true first step of this is to obtain a speedo gear that will work for your set up. The dealers call it a "pinion speedo drive"" and the part numbers are 5206 76XX where the "XX" is the number of teeth. For example: The part number for the 31 tooth gear I needed was 5206 7631 and a 34 tooth gear is 5206 7634 and so on.

Once you have the correct speedo gear in hand it is simply a matter of removing one bolt (13mm) that holds the metal tab that holds the housing in. The housing in on the side of the transfer case, you can't miss it. Once that is off you can simply wiggle it and pull it straight out. Be careful of dripping fluids. If you happen to be doing this soon after driving your Jeep then the fluid could be hot. I would suggest waiting for the vehicle to cool down, about 15 minutes should do.

The actual gear itself can now be pulled free. A firm tug is really all you should need. It should be noted that the gear will usually be covered in fluid so you will want to have at least some paper towels handy to wrap around the gear when you pull it out of the housing. To install the new gear you just push the new speedo gear into the housing (metal end first) until it pops into place. Make sure that it is pushed all the way in and none of the metal shaft is showing.

The next step is the most important one. On the outside of the housing you will find a few different sets of numbers (26-31, 32-36....). What you need to do is twist the housing until the numbers that your new speedo gear is in are lined up so that you can insert the metal tab and the number can be read with you looking toward the front of the Jeep. The position is determined by the bottom slot that the fork fits into. If the new gear is not in the same range as the old one and you do not correct it then your speedometer will not work at all.

Once you do that you simple reverse the steps and put everything back together. To test your speedo take a drive, a highway is the best place to do this, and get up to 60 mph. Then check your odometer between each mile marker for about 5-10 miles. Traveling at 60 mph you should be going 1 mile per minute. If after your test you have not gone 5-10 miles according to your speedo you are still off. If you are pretty dead on then you are set.

I know there are several articles out there on this simple procedure, but most of them forget to tell you to check the housing and adjust it properly. That one ommitted step bite me in the rear and I had to fix mine in the dark using a flashlight. No fun at all!!!!

The chart below has been recently updated to be more accurate, based on true GPS readings and user testing.

R/P Ratio	Tire Size
	30"	31"	32"	33"	35"	36"	37"	38"
3.73	34	33	32	31	29	28	28	27
4.11	40	38	37	36	34	33	32	31
4.56	43	42	40	39	37	36	35	34
4.88	46	44	43	41	39	38	37	36

[Yucca-man]

Argh - there's no 3.55 in there, but then again maybe that's a hint that one of my next steps needs to be a regear.

[RokBox]

Need a 3.55 # as well...or gears....glad im not the only one

[Bulldog 6]

Charts can help but not all tires are created equal in size. Not all 31s" are the same size. Here is the math on how to calculate what you need. I am not the creator of this as it was obtained from other Jeep sites, but the math is correct in how to figure stuff up.

It is 1 equation so you can only have 1 unknown and that is what you want to solve for. If you are solving for which speedo gear to buy then you must know old and new tire size as well as number of teath your current gear has.

G2 = (g1) X (T2) / T1

Hope this helps.

[Yucca-man]

Okay, after regearing the rear to 4.56, I have power to the ground again. For those of you who don't get the concept, it's like riding a 10-speed but always starting out in 5th gear...you can do it but it takes awhile to get up to speed. Same thing with a 3.55 geared XJ with 32s.

Anyway - looking at yon handy chart, I deduced that I needed a 40-tooth speedo gear for the 32s and 4.56s. It took a whopping four minutes to make the switch, and most of that was spent trying to find the right wrenches. Had I just looked underneath first, I could have saved a lot of that time and simply grabbed my sockets because there's that much room.

A 1/2" wrench fits just fine. Undo the retaining bracket, pop the housing out and remove the old gear. This step took me some time because the old gear had been in there for 170,000 miles and was very set in it's ways. Pop the new one in eventually, clock the housing and tighten it down. "Git 'er dun" as Larry would say...

I did a measured 60 miles on I-25 immediately afterward during a drive to Denver, and the odometer dropped 0.4 miles one way. On the return trip, it showed 59.8 miles on the 60-mile stretch. I can live with that teeny bit of inaccuracy. I could probably adjust my air pressure to make up for it, but that's just excessive.

Jim