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60mph 6th gear rpms 4k speedo 12 miles over! Need Help

60mph 6th gear rpms 4k speedo 12 miles over! Need Help

Old 01-17-2018, 09:54 AM
  #1  
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60mph 6th gear rpms 4k speedo 12 miles over! Need Help

Hello s2k owners, out of many s2ks i have purchased and worked on i have never seen the issue i am dealing with now. I do apologize for my english, let me know if anyone has anything to say.

Recently bought an 05 s2k 40k miles with no history from the past. First time i drove noticed that the speedo is reading higher from the actual speed, compared it to the gps tracker and i was 11 to 12 miles over the actual speed on the highway. I did read that some people's cluster had issues and people recommend installing a yellow jacket to compensate for the issue. The car is stock ap2 with matching vin number on the block/tranny. I checked the ecu and it is an ap2, i swapped clusters, and speed sensors and nothing has changed. I did read about different gears being installed in the diff like the 4.44 all the way to 4.77 and from reading it seems that ap2 with 4.77 would be 700 to 800 rpm higher ( would that be enough to offset the speed by 11 to 12 miles?).
Does anyone here run an ap2 with different diff gears and had the same issue with the speed?
I had put the car on the lift and examined the rear diff,bolts, anything to tell me that the diff at some point was out and swapped out and everything looks too clean, no scratches no nothing indicating different gears inside. If we are to say that the car is fully stock, what else could be going on that would cause the RPMS to be at 4k at 60 and have 11 to 12 miles over the speed?
Is there any way of checking the diff manually? by lets say marking, spinning counting how many revolutions i get with the oposite side axle then compare that to a stock diff or another diff? anything to see if the gears are different?
I do apologize for my english, let me know if anyone has any input.
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Old 01-17-2018, 05:47 PM
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I've seen this issue before. It's possible that a previous owner had larger wheels on the car, and re-calibrated the speedo for that setup.
At some point in time, stock wheels went back on the car, and the speedo was never reset.

It's discussed a bit here:
https://www.s2ki.com/forums/s2000-un...-962574/page3/

Good luck
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Old 01-17-2018, 06:41 PM
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Hello, figured it out. The car did come with 18's but that was not the problem. It was a 4.77 diff in there, installed a stock diff today and all is back to normal.... Thank you
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