New to Jeeps and needing help

Big Bill

Big Bill

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Joined
May 16, 2021
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Location
Phoenix AZ
I recently bought my first Jeep. (2006 Rubicon Unlimited) The jeep already had some upgrades including 33/12.5/15 tires and 4.88 gears. I put 35/12.5/15 tires on and now noticing the transmission shifting hard. I bought a Superchip Flashpaq F5 to adjust the tire size and gears in the computer but it didn't work. Luckily I am able to return it.
Has anyone been able to make those changes, and what did you use?
 
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HPTuners is able to access the jeep's computer but it won't be able to recalibrate the tire size. It can adjust transmission shift points though. There is a unit called a Speedohealer that will correct the speedometer.

Regarding the trans, I assume it is an automatic? Start by checking the transmission fluid level. With the engine and transmission fully warmed up and idling, it should be towards the upper fill mark on the dipstick. A but of overfill won't hurt, but underfilling will cause issues.

4.88 gears and 35s is generally tolerable, but far from ideal. Most on here recommend running 5.38 with 35s and the automatic. (4.88 is recommended for the 6 speed manual.)
 
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WranglerFix ECU for that hard 1st to 2nd shift and for your speedo, this from a how to post:

How to Correct the Speedometer on Rubicon Models
This above speedometer gear change not work on 03-06 Rubicon models. The speedometer on these is electronically controlled and therefore you only have two options:

1) Some dealers are able to re-program the ECU so that it the speedometer will accommodate for different gearing and larger tires.

2) There are several electronic speedometer calibrators out there, but the one I suggest is the Speedo Healer by Blue Monkey. It's 100% plug-and-play, and uses factory style connectors. Note that you can also use one of these speedometer recalibration modules on a non-Rubicon model (as oppose to swapping the speedo gear as outlined above), but I'm not sure why you'd bother wasting the time and money, when swapping the speedometer gear is both cheaper and easier.

https://wranglertjforum.com/threads...ometer-after-changing-tire-sizes-or-gears.83/
 
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Big Bill said:
I recently bought my first Jeep. (2006 Rubicon Unlimited) The jeep already had some upgrades including 33/12.5/15 tires and 4.88 gears. I put 35/12.5/15 tires on and now noticing the transmission shifting hard.
Click to expand...
The hard 1-2 shift is common, and not because of the 35" tires. You can see if the Wranglerfix PCM will help by disconnecting the battery (to reset your PCM) and then the problem goes away for a while.

Pretty good choice for a first Jeep.
 
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Yes, I have the 12 o'clock labs speedometer corrector. It has been perfect so far and works on ALL TJ, not just Rubicon. You can re-program it as many times as you need as tire size and gears get changed.

https://www.ebay.com/itm/3033314840...d=link&campid=5337789113&toolid=20001&mkevt=1
This listing says for LJ but it will work for ALL TJ's. There is probably another listing for same part # that says it for TJ's. The harness comes with factory style connectors that go between the transfer case output and the PCM input, at the transfer case. The harness is about 6 feet long and the actual, tiny module is on the other end. I had it above the transfer case near the rubicon locker pumps until I moved it all under the hood.
 
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