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Thread: Auto tranny boggin' on the highway...

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    Senior Member E5EDDIE's Avatar
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    Default Auto tranny boggin' on the highway...

    My A/T doesn't want to downshift on hills at speed on the HWY, tires are 32", bunch of extra weight on her, can the tranny computer be adjusted to the new tire size?
    "What is life without honor? Degradation is worse than death!"
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    Mountain Valley Customs
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    Did you change your speedo gear to account for your larger than stock tires? Your tranny uses info gained from the speedo gear for shift points. Also, how many miles on the tranny and when was the last time that you changed the tranny filter? Are you still running your stock gear ratio? If so, what ratio do you have? If you have a 4.0 than you more than likely have 3.73s, but it could be 3.55s. Incorrect gearing will also have the effect you are experiencing.
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  3. #3
    Administrator korisu56's Avatar
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    He's got a Rubi Rob.

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    Land Squid Jeffb_79's Avatar
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    I wouldn't think the 32's would affect it that much, I just put 33's on my rubi not too long ago. If you're on the highway or going through the hills, turn your o/d switch off. You're rpms will be up, but it will help with the constant bogging down and shifting.

    You can't do a speedo gear to get your speedo back on track, but can get it taken care of at the dealership. However, with 33" tires I'm only down about 6% on the speedo.

    Your next option is going to be to re-gear. I don't think that's even close to being worth it on 32's though. Wait till you go up to 33's or 35's and then throw a set of 4.88's or 5.13's in it.

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    Junior Member CJ2aChad's Avatar
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    I hate automatics....
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    Mountain Valley Customs
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    Quote Originally Posted by korisu56 View Post
    He's got a Rubi Rob.
    Ahh, my bad. I didn't know that.


    Quote Originally Posted by Jeffb_79 View Post
    You can't do a speedo gear to get your speedo back on track, but can get it taken care of at the dealership. However, with 33" tires I'm only down about 6% on the speedo.

    Your next option is going to be to re-gear. I don't think that's even close to being worth it on 32's though. Wait till you go up to 33's or 35's and then throw a set of 4.88's or 5.13's in it.
    x2 on what he said. We've had a couple Rubis taken care of for us by our local Jeep dealership.
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  7. #7
    Do it right or not at all Jerry Bransford's Avatar
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    The 4-speed automatic used in 2003 and newer TJs has a very deep overdrive ratio so the engine can lug on the highway, especially when bigger tires are installed. There is a software update for that particular transmission if the Rubicon is an older model but if that doesn't help, the only sure way to cure this is to regear the axles to a lower ratio to raise the engine RPMs back up to where they should be.
    See the Geezer Jeep at http://members.cox.net/jerrypb/

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