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KJ gearing


 
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plazanas
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Joined: 24 Aug 2004
Location: Greece

PostPosted: Tue Aug 24, 2004 5:53 am    Post subject: KJ gearing Reply with quote

Hi guys. I live in Greece and since 2002 I drive a Liberty 3.7 ltd. In Europe they call it Cherokee...
Anyway, even though the engine is typically more powerful than my previous' Cherokee 4L, the feeling I get from the car is sluggish. I have a feeling that the gearing (3.73) is too high and I am thinking in getting 10% lower (4.10). Anyone has any experience/suggestions? Would such a change confuse the electronically controlled automatic gearbox? (which by the way seems to me very uncivilized and slow)
Thanks,

Panos
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ThePhantum
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Joined: 23 Jan 2004
Location: I knew it...I'm surrounded by Assholes!

PostPosted: Thu Sep 02, 2004 1:11 am    Post subject: Reply with quote

The Transmission Control Unit (TCU) determines the shift points based on input given by the Electronic Control Module (ECM). Throttle postion, speed, current engine RPM, etc. are all taken into consideration.

If you lower the gearing, your speedometer is going to read faster than you are actually moving, causing the TCU to shift gears sooner than you would like it too. In order to have the transmission shift at the correct points, you should have your speedometer recalibrated.

HTH
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plazanas
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Joined: 24 Aug 2004
Location: Greece

PostPosted: Thu Sep 02, 2004 1:18 am    Post subject: GEARING KJ Reply with quote

I Thanks you for your replies. Just a question: I thought the speedometer read from the wheel spin and not from the shaft, in which case only the different tires should affect it. Even if I am wrong, though, changing gears sooner might work positively, as with the lower gearing the torque at the wheels should be enough to tolerate sooner gear changes. Not true?

thephantum wrote:
The Transmission Control Unit (TCU) determines the shift points based on input given by the Electronic Control Module (ECM). Throttle postion, speed, current engine RPM, etc. are all taken into consideration.

If you lower the gearing, your speedometer is going to read faster than you are actually moving, causing the TCU to shift gears sooner than you would like it too. In order to have the transmission shift at the correct points, you should have your speedometer recalibrated.

HTH
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ThePhantum
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PostPosted: Thu Sep 02, 2004 1:21 am    Post subject: Reply with quote

On Jeeps, the speedometer usually takes it's reading from the transfercase...so regearing and/or bigger tires will affect it. Wink

edit - I should point out that 2wd models take the reading from the transmission itself.
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ThePhantum
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PostPosted: Thu Sep 02, 2004 1:34 am    Post subject: Re: GEARING KJ Reply with quote

plazanas wrote:
changing gears sooner might work positively, as with the lower gearing the torque at the wheels should be enough to tolerate sooner gear changes. Not true?


It depends on how far a jump in gearing you make. Going from 3.73 to 4.10, it most likely is true...you might not even want to bother recalibrating. Based on your other post though, it sounds like you want to lift it too...which most likely means bigger tires as well. I would say wait until that is done prior to regearing. There is no sense in gearing to 4.10 now when you might want to go 4.56 later...you could use that money for another modification. Wink
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