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4.88 Speedo Change

898 views 9 replies 6 participants last post by  hineyman 
#1 ·
I recently regeared my axles from 4.10's to 4.88's in my '98 TJ. I have no clue how far my speedometer is off now. I run 32" BFG A/T's and it's a 2.5L if that matters. I have a feeling it's reading 5 mph faster.
 
#3 ·
Don't use the speedo, use the odometer. Find a road with mile posts and drive 2-5 of them and see how far off your odo is compared to real (percentage). Then buy a speedo gear that same percentage different than what you have now. If you read lower than real, buy less teeth. If you read more miles than real, buy more teeth. What do you have now? Pull it and see, crawl under your Jeep with a 1/2" wrench. Be sure to get the plastic housing rotated to the right position for the tooth count you have and will buy.
 
#8 ·
Drive 1 mile, if the odometer reads 1.1 then you are 10 percent over. Get a new speedo gear with 10 percent more teeth than the one you have.
 
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