I have ran my 97 TJ with proper speedo gearing and without and there has been no difference in performance.
Same for me... In my case I calculated ACTUAL (meanining that I corrected for the difference between what the speedo showed and what was the real mileage) mpg before and after, and there is no difference. I do plan to keep mine calibrated, though, if only to know what speed I am driving at!
So is this replacement speedometer gear a universal or is there a specific one I need to order?
You will need to calculate which gear you need based on te gear ratios and tire size you have. There are plenty of charts out there to use as a guide, but if I am not mistaken, the Jeep (at least my YJ!) comes stock with 41, and you have to drop to 38 for 31" tires and 4.10 gears in the diffs. I bought my gears from Quadratec, by the way.
What's invovled in installing calibrating, or does simply installing a new fix the calibration? Or does a mechanic/dealer have to do it?
You can do it yourself in less than minutes with a socket set... Take out ONE screw, pull out the old gear, insert new gear, screw back into place. Just note that the whole speedo assembly is rotated when you go to 38 teeth or less (that's indicated on the assembly itself). If you do not insert it the right way for a 38 tooth gear, the gear will fall off (ask me how I know!).
