don123160

I have a 2014 JKU and it won't upshift sometimes unless I let almost all the way off the gas. Seems worse when cold. I've noticed going up steep hills it really holds the gear long and doesn't shift. I've had a couple people ask if there's a problem with the truck when they heard it. I have 285/70/17 duratrac and AEV wheels. I haven't calibrated using Procal yet. Seemed to do this with stock tires as well, especially when cold. Only have about 1,000 miles on it and 3.21 gears. Has anyone else had any problems? Almost seems like the transmission software needs updated but figured dealership would be no help. Any ideas? Thanks

Mschneid

Once you change the tire size with the Procal you will be fine.

I still manually shift my auto when I feel it should up or down shift. That's what I like about this tranny, even in "D" if you push to the right it will up shift.

don123160

Yeah it didn't seem to happen right after I put on my wheels and tires - maybe 200 or more miles. It just seems overall a little more sluggish and not shifting at times correctly - especially on steep grades. I had the same setup on my 2011 wrangler with the 4 speed auto it it didn't really seem to affect it much. I was thinking maybe the newer 5 speed auto is more computer controlled and the difference in size effects it more. Hopefully Flashcal might help.

Thanks,
Don

don123160

Yeah it didn't seem to happen right after I put on my wheels and tires - maybe 200 or more miles. It just seems overall a little more sluggish and not shifting at times correctly - especially on steep grades. I had the same setup on my 2011 wrangler with the 4 speed auto it it didn't really seem to affect it much. I was thinking maybe the newer 5 speed auto is more computer controlled and the difference in size effects it more. Hopefully Flashcal might help.

Thanks,
Don

Valery Thompson

I got my first jeep Monday 2012 jk 38,000 miles with a super chip and well I changed the tire size from 30.50 to 37.50 cause that what size they are and now the tranny is acting all kinds of crazy what side I do?😒

JKJB

very strange. i have to ask since nobody else has but hows ur trans fluid level?

rob_engineer

Um, reprogram the computer for the larger tires? Just a guess

resharp001

you running 40" tires that are actually measuring 37.5"

Sixty4x4

Valery Thompson - First of all please advise what the gear ratio in the diffs are and what the transmission is doing. When you go to such a large diameter tire you are effectively increasing the load on the engine and tranny due to the higher gearing effect. Hence why a lot of guys go something like 4.88 gears with 37" tires to effectively keep the drive ratio at the diffs to about 4.10 (Rubicon ratio). Try driving in manual shift mode for a day or so and see how the engine performs for you. Sometimes with a heavy foot they tend to downshift easier under small acceleration requests. Other members here have stated that a change to large diameter tires almost requires a mandatory gear change as well.