automan21

Hey guys and gals. Think this is my first post here. Got a 2018 JKU last year and so for put a few mods on her. Couple of lights and bumpers nothing too crazy. My issue is its been shifting kind of strange. Lets say while doing 50mph i would slowly accelerate and and it would downshift then upshift like its trying to find the proper gear. Ive been driving manuals for the past 25 years and this is the first auto I've had in forever. Is this normal or is something off? All I did was change the 16" steel wheels to the 18" Sahara wheels. I used the super chips controller to adjust the wheel size for the speedo and the wheels are currently measuring 31.50. I don't want to damage anything on the transmission so I drive in tiptronic mode so I can control the shifting. My wife says its fine she doesn't notice a thing.

CJ3AtoJK

Yeah, something is off. Make sure you put a level across the top of the tire and measure the actual diameter of the tire mounted on the Jeep down to the ground. Don't use advertised tire diameters. I've got a 2015 JK Rubicon with the 5-speed auto and I changed the gears from 3:73 to 4:56 waiting for my 35" BFG KM2's and rims to come in and get mounted. I had to drive the Jeep a few weeks on the Rubicon factory BFG Mud-Terrain's waiting for my rims to show up, they were on back order. I used the Flash-Cal to calibrate the gear ratio and I changed the tire diameter to what I thought was the factory advertised tire diameter, and it wasn't right. I forgot the actual tire diameter to the ground, but it was shorter than the advertised. The 5-speed auto was down shifting when it didn't need to, over rev-ing the engine a bit, it was also stacking shifts, and going through all the gears too quick and kind of bogging the engine when it got to 5th. I reread the Flash-Cal directions and it said to measure the actual tire diameter, mounted on the vehicle, to the ground, I changed it,and it started to shift perfectly again. After my rims finally got in and I got my 35"x12:50"x17" BFG KM2's mounted, I checked the actual tire diameter at the tire shop with a level & tap measure. Mounted on the Jeep at 35 psi., the actual diameter of the rear tires to the ground was 33.625". I entered 33.6 into the Flash-Call and my Jeep shifts great. I'm not sure this is your problem, but this is what I ran into.....I hope it helps.

automan21

Well I double checked the wheel/tire size. Instead of 31.50" is actually 31" so I changed it with the Flashcal. Not sure if a half inch change would make a difference on the shifting but I will find out tmrw.