Recalibrating Speedo

I know that since I went up to 31 inch tires my speedo is off. I was looking at the Cherokee America web-page, and there is an excellent chart on the correct gear to use. Only problem is, mine is mechanical, not electronic. Is the procedure the same? Also, do all the XJ's use the same or similar gears? Thanks!

SPSERG said:

I know that since I went up to 31 inch tires my speedo is off. I was looking at the Cherokee America web-page, and there is an excellent chart on the correct gear to use. Only problem is, mine is mechanical, not electronic. Is the procedure the same? Also, do all the XJ's use the same or similar gears? Thanks!

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Procedure is the same as whether it's electronic or mechanical you have to change that plastic gear. The difference (based on year) is whether you ened a short shaft gear or long shaft gear: once you figure out how many teeth you want, call whoever you are going to be getting it from and tell them a the year and nubmer of teeth and they'll do the rest.

Got it, Thanks!

http://jeepin.com/features/speedogear

Procedure is the same, mechanical and electronic speedos use different gears though. Same teeth count, just different lengths/part numbers.

Thanks for all the replys, but at the risk of showing my ignorance... I looked over the chart, with 3.07 gears and 31 inch tires the chart says I need an SG-27 gear. At the Jeeps unlimited page it lists the Mopar part numbers in tooth size and there is no 27 tooth gear. The SG-27 is relative to tooth size?Could you enlighten me??

SPSERG said:

Thanks for all the replys, but at the risk of showing my ignorance... I looked over the chart, with 3.07 gears and 31 inch tires the chart says I need an SG-27 gear. At the Jeeps unlimited page it lists the Mopar part numbers in tooth size and there is no 27 tooth gear. The SG-27 is relative to tooth size?Could you enlighten me??

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Not all tooth sizes are made. You might have to go aftermarket or go a tooth up or down.
Anyways, keep also in mind that none of those charts out there are 100% accurate: it all depends what they used as a basis for their calculation (which not necessarily was accurate in the first place as the jeeps came with two tire options ussually but same speedo gear).
Also GPS testing of the speedo gear isn't as accurate due to the lag and fluctuation of the needle and hte lag on the gps. Best way to test it after new speedo gets installed is to go out on a highway and test it on about 10 or more mile marker posts.

Also not all 31"s are created equal, so the closest you can get the best.

I found aftermarket gears at Teraflex, and they have the 27 tooth gear. Only problem is they list long and short shaft, and according to their application guide, the long shaft fits 1987-95. The gear itself changes after 1990 to a different shaft correct?

I've had my 31" bfg AT's for the last two years and I always thought my speedo was a little off. Today I had the oppertunity to borrow a buddies GPS. I found my speedo to be dead nuts 119km/h speedo = 120 km/h GPS

I couldn't believe it but thats what it said

Last night, I broke out the GPS and went for a spin. On the highway, its between 8-9 mph off. i.e. reading 55 when the actual speed is almost 65. Going to order a new speedo gear on Monday.