If you hav tranny issues, u might consider a reflash for tire size - JKowners.com : Jeep Wrangler JK Forum
 
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post #1 of 8 Old 05-16-2011, 06:42 PM Thread Starter
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If you hav tranny issues, u might consider a reflash for tire size

I run 37's on my unlimited and the tranny was not shifting correctly, it was holding gears for too long and not down shifting when it should have been there seem to be a loss in power and my mpg dropped drastically.

I re-measured my tires and sure enough,. they were worn down about 1.75" so in turn was screwing up the computer. After a reflash and set it to 35.25", the shift point are now corrected.

Just wanted to share and something to consider if you have had your tires on for a while with no current flash.

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post #2 of 8 Old 05-16-2011, 11:52 PM
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Good info. I can chime in from experience... Yes its VERY important to reflash after both, regearing and tire size change for the auto guys. And if you do a lot of HWY driving its even more important.

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post #3 of 8 Old 05-17-2011, 05:52 PM
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Good info. I can chime in from experience... Yes its VERY important to reflash after both, regearing and tire size change for the auto guys. And if you do a lot of HWY driving its even more important.
How do you reflash?
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post #4 of 8 Old 05-17-2011, 08:06 PM Thread Starter
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How do you reflash?
you need a programmer. it's called "flashing" After gear install (different from stock) or bigger than stock tires, you need to do this for the automatic transmission to correct the speedometer and transmission shift points.

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post #5 of 8 Old 05-18-2011, 05:52 AM
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You can hear some little vibration when I'm idle sometimes, or around 50kmh uphill...
I will correct my tire size tonight.
Pretty sure the vibration at 50kmh will go away... (I know my config is not accurate for sure...)
Thanks for the tip!
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post #6 of 8 Old 05-18-2011, 07:46 AM
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they were worn down about 1.75" so in turn was screwing up the computer. After a reflash and set it to 35.25", the shift point are now corrected.
Good point about setting the correct tire size, but they can't wear down 1.75", they were just never 37" to start with.

Easiest way to check if you have the correct tire size programmed is compare the speedo to a GPS.
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post #7 of 8 Old 05-18-2011, 07:04 PM Thread Starter
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Good point about setting the correct tire size, but they can't wear down 1.75", they were just never 37" to start with.

Easiest way to check if you have the correct tire size programmed is compare the speedo to a GPS.
ok so originally they were 36.9, close enough. These Pro Comp tires were damn near true 37's. I programmed it when the gears and and tires were put on over 2 years ago and the last 6 months or so, no one could figure out why the tranny was acting the way it was. I measured it back then and I measured it now, so I do know what it was before the tires even hit the pavement.

The speedo was correct until last year when everything started going to crap on mpg and the tranny shifting. Now that I did this, I have the power back, mpg went back up, and tranny is shifting when needed

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post #8 of 8 Old 05-18-2011, 07:08 PM Thread Starter
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by all means, I am not dismissing anything. I am open to ideas. Maybe there was some underlying cause for my issues, but all I know is that I measured the tires now and re-programmed it, now everything works great

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