No throttle in 8th gear.

[Headbarcode]

Definitely get your jeeps reprogrammed for the bigger tires. Not only wil it make fuel data and the speedo accurate, but the tranny relies on actual speed on top of other factors to determine the optimal shift points for the situation at hand. The ZF 8-speed auto is a very intelligent learning unit, but still requires being told of any changes to avoid it making decisions based off of wrong info.

Depending on your own intended use, that may be enough to avoid the additional cost to regear. If a regear is done, same thing applies as far as needing to regrogram that change so the tranny can compensate and adjust.

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[The Acme Company]

I can’t speak to your lack of throttle response but I learned tire size vs gearing years ago with my 4x4 2.8 liter Ranger.

Went from stock street tires to 31.50 x 10.50 15’s without an issue. Wore those out and moved up to 33’s. Lost a little power but still drives LE. Then we lifted it and went to 35’s. It had no power at all. The little 6 with a 5 speed did not have enough power to overcome the lack of gearing. Throttle response was nill.

There comes a point where you have to change the gear ratio to match the tire size.

 

[Bill G]

I’ve got the 4 door Sport S with the 3.45 stock gearing, threw some Falcon 35s on (which 34.25). Prior to flash I was getting 16 mpg combined, after flashing I’m at 18. Did an out an in for a dove hunt last weekend and was at 21 mpg. I know the math for tire to gearing ratio (34.25x3.45 31), so I’m thinking 3.77. Oh and I see 8th all the time.

 

[The Acme Company]

Going to 35’s with at stock 3.45 ratio will not get you 3.77. Maybe 2.77. If you have enough hp to turn the tires in 8th gear and a ratio of high 2’s should increase mpg.

Would be a 0-60 dog compared to 4.11’s or 3.73’s—even with the bigger tires.

 

[ToolMan514]

Well, 6th gear is 1:1 to output and 7th and 8th are both overdrive, so it's not surprising. The gear ratios are available in this post: https://www.jlwranglerforums.com/forum/threads/gear-ratio-chart-for-jl-wrangler.1781/#post-141841

 

[Sjpunx]

Not sure if this is normal or not. I have 35s on my 3.6 sport with automatic. I have not reflashed the computer or done anything to calibrate it for the 35s.

I took a trip this weekend. I noticed while on cruise control at 75mph (gps indicated) the transmission was in 7th gear, which I expected from reading post on this site.

Just to try it out I put the transmission in manual mode and shifted into 8th. On its own the jeep slowed to 67ish while the cruise was still set.

I then turned the cruise off when back to automatic mode and got back to 75. Then shifted back to 8th. The jeep again began to slow down. I tried to give throttle to maintain 75, but there was no response.

I assume this is from having 35s and no changes to the calibration. I read of people saying it never shifted to 8th anymore after 35s until they re calibrated, but I thought it was wierd it would not let me maintain 75 when manually shifting to 8th.

I do plan to by a tazer, or maybe just have the dealership re calibrate it for 35s soon.

Thanks

James

You'll need to re-gear. I started with a 2-inch lift and 33's on my JL and even after flashing it, it still did not hit 8th and when it did it was a dog. Ended up gearing to 4.11 and all problems are solved

 

[wrangster]

I drive a sport with no lift and tires are 275/65/18 XL. My 8th gear is ok on level ground and down hill only I agree with most here that a re-gear to a minimum of 4.10 would be necessary for lift and 35's.

 

[WiscoJeeper]

Yeah, I understand the issue with the gearing, what seemed strange is that it seemed like there was no power, as in zero, as if the computer was not allowing any throttle. It was not acting sluggish or bogged down like if you are in too high of a gear, it was like the gas pedal was deactivated. Wierd, I was just wondering if that happened to anyone else.

James

I installed 35's on my Sport. I understand re-gearing. But, I am looking for the same answer as this guy was. I actually have the same issue. Put the transmission in manual 8th gear. Step on the accelerator, and get nothing. RPMS don't change. Speed of vehicle does not change. Is this normal? Is there something wrong?

Need to find a dealership that change the computer to tell it what size tire I am now using. My dealership are morons when it comes to Jeeps.

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