Auto Tranny question (based on a pet peeve)
- Thread starter jorgelrod
- Start date
Lil Nasty
Member
I use the tap shift on certain bridges around here (south Louisiana doesn't have hills lol) and when I'm towing a trailer down the interstate.
I've been curious about custom tuning for jeeps lately. Does anyone know of someone that focuses on jeeps? My GMC I had prior benefited greatly from the custom tune I had done.
JTPhoto JK
New member
I have an 08 with 5.38 and 37s. Flashpaq Tow Tune with which the transmission shifts much better. It doesn't hang like the factory or 87 octane tune.
When using stock tune I would manual downshift..
The transmission also has an adaptive memory so if you drive it easy it eventually gets sluggish and lazy. The cure is to remove battery cable for 10 minutes. Or just step on it once in awhile to wake it up.
When using stock tune I would manual downshift..
The transmission also has an adaptive memory so if you drive it easy it eventually gets sluggish and lazy. The cure is to remove battery cable for 10 minutes. Or just step on it once in awhile to wake it up.
RMC2
Caught the Bug
My understanding:
This is all true to a point. The transmission shift program is at least partly controlled by adaptive learning. It changes based on how you drive it. The 3.6 auto tranny computer (i believe 13 or newer, and not the 12) is a different beast than the older auto in the 3.8. It is a seperate module and from what I have read, much more difficult to mess with because of this. I don't know if any companies have successfully broke the code on the transmission programming.
Now my experience:
My 13 started having problems holding on to a gear when climbing also(even at slow speeds and sections of road that were much flatter). It did not originally have this problem. I also have a twice in the morning hesitation within the first couple of hundred yards. That only happens the first drive of the day. It did not originally do this either. One service tech said it was very noticeable and they reset everything and updated the transmission programming (there is an update). After a few hundred miles the hesitation came back. I don't know if the other shifting problem came back because I moved 1500 miles away, but I haven't noticed it on shorter hills. I took it back for an oil change and mentioned the hesitation had come back. A different tech this time, and he says there is nothing wrong with it and that it is 1. Normal and 2. that I should let it warm up before I drive it.
I believe this is nothing more than a computer programming bug and Jeep doesn't really care to spend effort(costs money). Also, it doesn't matter who makes a vehicle anymore, but most every abnormal problem is considered normal.
RMC2
Caught the Bug
I have recently began to think this too. Drive easy to save gas and i think the adaptive learning makes for a lazy transmission. Get "on it" a little more.
Yes I know, it is a jeep and not a prius. I have been driving my own 4x4's since 1989, but that doesn't mean I don't like getting good gas mileage too. My jeep mpg beats my truck though.
WJCO
Meme King
We just took our Jeep up in the mountains for the first time since the 4.56 gear swap (running 32 BFGs). It is the most enjoyable ride we've had since we bought the Jeep. The shifts weren't as harsh and also, it felt like it shifted like it should. Just nice and smooth with no complaints. We were amazed at the difference. And way more torque for hill-climbing.
croge17
New member
I have had a few different circumstances of this with different setups in my 13' jku.
factory 31's with 3.21 gears would hold gears on hills way to long.
35's with 3.21 gears was about the same
35's with 4.56 gears it holds gears towing up hills or on long grades under any acceleration
35's with 5.13 gears now it never holds a gear unless im towing a long hill
I think we are just terribly underpowered and dont realize what we have settled for.
factory 31's with 3.21 gears would hold gears on hills way to long.
35's with 3.21 gears was about the same
35's with 4.56 gears it holds gears towing up hills or on long grades under any acceleration
35's with 5.13 gears now it never holds a gear unless im towing a long hill
I think we are just terribly underpowered and dont realize what we have settled for.
MedixJK
-
That may be true, but they werent designed to be F350's, or corvettes. Lol
thardy
Banned
Wait, they weren't!? I have been SO misinformed!
MedixJK
-
I mean, that doesnt stop me from driving it like it is...
Lil Nasty
Member
I'm curious how was your fuel mileage affected with each gear set change? I'm sure as you increase numerically in gear sets, your highway went down, but did your city/highway average stay the same, increase or decrease? Just wondering as I've seen in the past not all vehicles need low rpms to get a better average fuel mileage.
croge17
New member
Stock was 17/18 with my style of driving
big tires and stock geras was miserable and only lasted a week or two
35's and 4.56 I was averaging 15/16
35's with 5.13 i average 17/18 again
Most my driving is a pure mix 10 miles highway and 10 miles surface streets and stoplights. Daily commute one way.
I really think that going by the tire charts everyone seems to refer to they fail to take into consideration rolling mass and rolling resistance. To get back to stock-like performance you have to go deeper than the chart suggests. By the ratio calculations the chart is right but the ratio alone doesnt take into account outside factors.
Lil Nasty
Member
That's what I was suspecting. Thanks for the information.
Clifford33
Caught the Bug
That's the exact question I was needing answered because I'm moving up to 35s / 315s and I'm wanting my power back and was wondering what gears to run. I also to slit of high way and city driving DD. And pull a lot of big hills man the 3.21 gearing sucks with even 285/75/16 tires. So would that be the ideal gearing is a 5:13 for a 35 inch. Again I do a lot how high way and high way hills. Hows it pick up on the high way? Can you get up to speed quick and stay with traffic? Also would love to see a video of you driving it to watch the rpms and mph on the high way. Man I hit up to 4,500 to 5,000 rpms up hill and am only going around 55 to 60. I don't get it my tires now aren't big. If any ones got some suggestions on what to do what love to hear the Feed back. Thanks!
Coop
Caught the Bug
This is a good point!
What gearing would have the 35/5.13 results noted for 37's?
jorgelrod
Hooked
5.13 with 35s? on a 3.8 or a 3.6?
I think the RPMs on a 3.6 with that combo would be close to 3500 RPMs at highway speeds
303jkpatriot
New member
Glad I found this thread. I have a '15 JKUR that is Auto and before i lifted and went to 35s it seemed to hold gears on slight hills and normal hills. I was starting to wonder if that was "normal" or not as I come up on 4k miles but it seems like there are others experiencing it so I feel a little better about it
ScoobyCarolanNC
Active Member
Yeah I have an auto, being that I live on a mountain I go up an down it every day
My jeep struggles half the time. It's like it can't make up its mind which gear to put it in.
Doesn't help Pennsylvania is nothin but hills.
I need a trans oil cooler lol.
Oil coolers not gonna help. How many miles? Been serviced on time? Right amount of fluid? Software update? I just went through a month of coming to peace with my auto 3.8.
jeeeep
Hooked
Yeah I have an auto, being that I live on a mountain I go up an down it every day
My jeep struggles half the time. It's like it can't make up its mind which gear to put it in.
Doesn't help Pennsylvania is nothin but hills.
I need a trans oil cooler lol.
if you have the 3.8, and are running larger than stock tires any incline sucks and you should get in the habit of locking out OD. with 35/315 IMO 4.88's are the best all around, this allows you to lock out OD on the inclines/hills and still be inside the needed rpm range and not pushing the upper limits. locking out OD you'll actually get better mileage and your transmission will last longer. If your transmission is always hunting for gears, it's heating up the fluid and making your engine work harder. A transmission cooler is recommended and a cheap upgrade in keeping your trans fluid cooler. if you're overheating the trans fluid you'll want to change it more often then what the manual recommends. Automatic transmissions do not like burnt fluid. The 3.8L "4-speed" IMO a 3 speed with a too tall OD, sucks big time.
If you're sure you are going to run 37" tires then I would go with the 5.13's but only if you have a Rubicon D44, PR44 or bigger up front, I wouldn't run 5.13's in a D30 the pinion gets too small. Before all the D30 owners running 37's get their panties in a bunch, yes it is possible to run a D30 with 37's. IMO the investment to "beef" up a D30 is not worth it and they still break, all the beefing up does it move the breaking point to a different area, the axle shafts, R&P don't change. if you can do all the work yourself, it's your dime and time. if you decide to run D30, 37's don't put a locker in it, you'll only speed up the "when" it breaks timeline.
I have a 2010 auto, 37's, 4.88's - it does fine all around but it was much better with the 315's, mileage, power etc... all a lot better with 315's. With the 37's it's ok but I do think 5.13's would be better. I always lock out OD pretty much everywhere I go unless it's flat and then I'll let it shift into OD. Freeway I still hit 70+ np and the mountain passes around 60-65, depending on how packed I am. mileage...hmm I don't own a jeep for its mileage but I avg 13-15 with the 37's
The 2015 transmission is so much better, I love that transmission lol, but it belongs to my daughter and she's told me hands off on the mods (she scares me a little :cheesy
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