Sponsored

Does Rubicon even use 8th gear??

BuffaloBill

Well-Known Member
First Name
Bill
Joined
Oct 14, 2019
Threads
4
Messages
352
Reaction score
466
Location
WI
Vehicle(s)
2018 Wrangler, 2014 Ram 1500 EcoDiesel 2020 JLUR Ecodiesel
My JLURD powertrain is stock. My tire diameter is 32.8". Under normal highway driving conditions at ~65 mph, in 8th gear, I am usually around 1,800 rpm. The ZF-sourced 8HP75 TorqueFlite 8-speed, does a good job keeping the diesel at 1,800 - 2,200 rpm, which seems to be the sweet spot. The Jeep powertrain engineers picked the right final drive ratio (3.73:1) for this vehicle. It's the best powertrain I have had in my Wranglers.
I agree about this powertrain. I too really like the 3.0. The engine, transmission, and rear axle ratio make it a pleasure to drive. Like you said, it seems perfectly matched for the stock tire size. It’s fun to drive!

Try running through the math once, assuming the rolling radius is half of the 32.8”. That works out to 615 rev/mile at the wheel. My dealer tells me the trans ratio on 8th is 0.64. Is that correct?

The stock K02 specs on tirerack shows that tire to be 635 rev/mile. That must be at rated load and pressure I imagine.

Anyway, using those two rev/mile figures, I come up with between 1590 and 1642 engine rpm @65. My tach indicates somewhere around 1600 at that speed (with stock K02), so I had concluded the 0.64 8th ratio may be correct. But I don’t know how accurate my tach reads of course.

Maybe our tachs read a couple hundred rpm different.

In the non-Winter months, I run 315/70/17 K02, which runs a bit less than the 35” I stated. With those, my tach shows 1500 @60.
Sponsored

 

calemasters

Well-Known Member
First Name
Allen
Joined
Sep 14, 2020
Threads
64
Messages
1,244
Reaction score
1,659
Location
Springfield, Mo.
Vehicle(s)
2021 Rubicon Unlimited, & Escalade
Occupation
Retired Mechanical Engineer
I agree about this powertrain. I too really like the 3.0. The engine, transmission, and rear axle ratio make it a pleasure to drive. Like you said, it seems perfectly matched for the stock tire size. It’s fun to drive!

Try running through the math once, assuming the rolling radius is half of the 32.8”. That works out to 615 rev/mile at the wheel. My dealer tells me the trans ratio on 8th is 0.64. Is that correct?

The stock K02 specs on tirerack shows that tire to be 635 rev/mile. That must be at rated load and pressure I imagine.

Anyway, using those two rev/mile figures, I come up with between 1590 and 1642 engine rpm @65. My tach indicates somewhere around 1600 at that speed (with stock K02), so I had concluded the 0.64 8th ratio may be correct. But I don’t know how accurate my tach reads of course.

Maybe our tachs read a couple hundred rpm different.

In the non-Winter months, I run 315/70/17 K02, which runs a bit less than the 35” I stated. With those, my tach shows 1500 @60.
My data shows the 8th gear ratio is 0.67. This is for the 8HP75 automatic. I do not have the data for the 850RE Torqueflite.

TRANSMISSION: 8HP75 AUTOMATIC, EIGHT-SPEED OVERDRIVE
Availability Standard — 3.0-liter EcoDiesel V-6 ESS
Description Adaptive electronic control or ERS driver-interactive manual control and electronically
modulated torque converter clutch
Gear Ratios
1st 4.71
2nd 3.13
3rd 2.10
4th 1.67
5th 1.28
6th 1.00
7th 0.84
8th 0.67
Reverse 3.30
 

beaups

Well-Known Member
First Name
Sean
Joined
Dec 6, 2019
Threads
1
Messages
743
Reaction score
1,230
Location
Ohio
Vehicle(s)
2020 JL
I beg to differ. Ever since Chrysler introduced the 604 4 speed overdrive back in 1989 the TCM adapted its shift algorithms to the drivers habits. Back then we had many complaints from rental car companies stating the transmissions were not shifting correctly. That was caused by so many different drivers operating them. Since then, the adaptive memory learning period is much shorter, thereby it is not a noticeable issue anymore. Most if not all modern TCM's do the same thing. Chrysler tech for 26 years, then still in the industry the last 15+ years.
You can differ all you want, but you’re still wrong. The ZF8 adapts to itself - clutch wear levels, fluid viscosity, etc. it does not adapt to it’s drivers’ long term habits.
 

Quadjeeper

Well-Known Member
First Name
Scott
Joined
Apr 22, 2020
Threads
0
Messages
316
Reaction score
689
Location
Winter Springs, FL
Vehicle(s)
2022 392XR
Occupation
retired
You can differ all you want, but you’re still wrong. The ZF8 adapts to itself - clutch wear levels, fluid viscosity, etc. it does not adapt to it’s drivers’ long term habits.
Each is entitled to his opinion.
 

Stuckinthesand

Well-Known Member
First Name
CJ
Joined
Apr 6, 2020
Threads
21
Messages
844
Reaction score
965
Location
NJ
Vehicle(s)
2019 Wrangler Sport S
You can differ all you want, but you’re still wrong. The ZF8 adapts to itself - clutch wear levels, fluid viscosity, etc. it does not adapt to it’s drivers’ long term habits.
The Auto trans has adaptive learning..........you drive with a heavy foot, The shift points learn to shift at higher rpm's to adapt too your driving style. You drive with a light foot the shift points will move downward to lower rpms over time.

Pull the trans control module fuse for a minute and re install. (resets the trans to default) Go for a drive with a light foot and see what happens.

Reset trans then Re cal your speedo as well if you upgraded to bigger tires.

This is coming from a ChryslerASE master tech with over 30 years of experience. Believe what you want. I tend to believe the pros. .
 

Sponsored

jeepoch

Well-Known Member
First Name
Jay
Joined
Nov 13, 2019
Threads
1
Messages
951
Reaction score
2,687
Location
Longmont, CO
Vehicle(s)
2019 JL Wrangler Sport S 3.6L Auto 2 door, 2.5" lift, 35s
All,

On my lifted 2019 Sport 3.6L 2 Door on 35s with the stock 3.45 m186/m200 axles, I like using the AutoStick feature at highway speeds to manually select 8th whenever I believe it should. Then I down or upshift as if driving a manual.

Previously with the stock 31.5 inch Michelin's, achieving 8th gear was both routine and rather frequent. However, now with these 35's, 8th gear truly is an overdrive on steroids.

Yet it didn't take very long after manually selecting 8th for the ZF to puzzle out I like overdrive. It automatically selects 8th way more often now on it's own. Not as regularly as with the stock tires but now may more than before I started coaxing it there.

I have also configured my EVIC to indicate the current gear. This really is a convenient aid to watch what the trans is physically doing. I'd highly recommend everyone set their cluster configuration this way. I'm really amazed this isn't the default normal setting from the factory.

When in Drive it now shows D1-8, and when in AutoStick it shows just 1-8. Watching it run through the gears is pretty amazing. Within the middle range I see the gears change but rarely feel any shift at all. The shift points are smooth, quick and intelligent, especially downshifting to a stop. This trans even downshifts more aggressively depending on the amount of brake peddle applied.

I used to be a manual trans junkie. With this 8-speed, I'm beginning (maybe way past) not missing the clutch peddle in the slightest. I can easily select whatever gear I want, anytime I want, and the ZF just does it. No questions asked. Just like a manual. Even if I infrequently forget it's in Autostick mode, the ZF acts just like a manual would. But instead of either stalling, or over-revving, it's smart enough to just adjust itself accordingly into a more appropriate gear.

When off-road, very (very) seldom do I ever have it in Drive, especially in 4Lo. The absolute control of the gears without clutching when climbing over obstacles or maneuvering over rough terrain is so incredibly cool. Riding the clutch now, for any reason, is a thing of the past. This ZF just almost instantly responds.

This JL has the best powertrain I've ever driven. It is by far the best daily driver and light utility vehicle I've ever owned. Certainly by far the most fun.

It is really sad to hear how some Jeepers are having issues or are dissatisfied with their JL's. This has NOT been my experience. I'm having a blast. Love driving this thing everytime I get in it. No matter the destination. I find I even sometimes just go cruising with no intended purpose. Almost always somewhere here within the foothills along the Colorado Front Range, where I call home.

Jay

Jeep Wrangler JL Does Rubicon even use 8th gear?? IMG_20200801_200022
 

DadJokes

Well-Known Member
First Name
Daniel
Joined
Oct 22, 2019
Threads
75
Messages
2,496
Reaction score
2,119
Location
Indiana
Website
www.youtube.com
Vehicle(s)
Sahara
In regards to getting to 8th gear,

On these more sophisticated computer controlled vehicles the last 10(?) years, I’m sure there are thresholds (load)that need to be met in order to get the shift to happen aside from only mph minimums but what if you lied to the computer? What if you overcorrected and entered a larger tire diameter than you actually have? Would that help lower the real world mph threshold factor possibly getting more frequent conditions for the shift to happen? Even if it did, you wouldn’t want to go too far or you’d be racking up miles you never traveled.
 

JustinB

Well-Known Member
Joined
Nov 23, 2020
Threads
6
Messages
141
Reaction score
149
Location
Arkansas
Vehicle(s)
Jeep Cherokee, Ninja 650R, Jeep 392, Yamaha TTR230
Is anyone re-mapping the ECM/brain to accommodate for the larger tires which, in theory, would change the shift point???
 

Hound Dog

Well-Known Member
First Name
Don
Joined
Sep 21, 2020
Threads
15
Messages
356
Reaction score
514
Location
Haymarket, VA
Vehicle(s)
2020 JL Rubicon, 2002 TJ Rustomatic
Mine has 35" Duratracs and it sees 8th. When driving down a 10% grade and a minimum 20 mph wind pushing at the back.

Probably because I have a bit of a heavy foot. I think it would see 8th a bit more if I kept under 65. I think above that the wind resistance to the brick on wheels keeps it in 7th.

When I wear out these tires and go for the lift and 37s we'll see what new gears will do for it.
 

Sponsored

Headbarcode

Well-Known Member
First Name
Mike
Joined
Aug 16, 2018
Threads
26
Messages
7,782
Reaction score
17,830
Location
LI, New York
Vehicle(s)
2019 JLUR Stingray 2.0 turbo
Vehicle Showcase
1
Is anyone re-mapping the ECM/brain to accommodate for the larger tires which, in theory, would change the shift point???
Yes, most are accomplishing that with a Tazer. Read more about it at zautomotive.com

And yes, a correct speedo is one of the factors used by the 8-speed to optimize its shift points.
 

Rubycon50

Well-Known Member
First Name
Royce
Joined
Dec 21, 2019
Threads
12
Messages
113
Reaction score
130
Location
Glendora, California
Vehicle(s)
2018 Jeep Rubicon JL
Vehicle Showcase
1
Some basic stuff:
  • Assuming you purchased new so nobody else has messed with your software settings?
  • Is your automatic transmission fluid at the right level?
  • Are any of your transmission lines wet with oil?
  • Is your engine flaring or abnormally revving when under load?
  • Do you have DTC's (error codes on the screen)?
  • Has your ATF ever been changed? No need at 2500miles.
  • Wheel speed sensors in the JL's tend to poop themselves pretty easily but you would know about it.
  • Do you have a tazer or other software controller on the jeep? It's worth ruling out incorrect tire size like previous posters have mentioned but...if you purchased it new and you have not added a Tazer and played with the settings you should be ok.
  • Are you on relatively flat ground when trying to go into 8th. Going uphill or being heavy on the gas pedal is not going to help.
I had 37's with 4.10 gears and could get 8th but I had to be nice and be on a level road. I changed to 4.88 gears with 37's and it now slides into 8th routinely.
 

Howardlv22

Well-Known Member
First Name
Howard
Joined
Jan 11, 2021
Threads
17
Messages
250
Reaction score
475
Location
Arizona
Vehicle(s)
2021 JLU EcoDiesel
I have the 2021 JLU with stock dana 44 front and rear, stock gearing and the 3.0 ECOdiesel. My jeep isn't light, I've upgraded to 37's, and black rhino wheels, new bumper tire carrier, 4" lift, etc. I have the taser mini and my tires and speedo are calibrated perfectly. I see 8th gear ALL the time. I think its a torque thing, my diesel has so much freaking torque compared to my old 3.6 and my buddies new 2.0.
 

Yogi

Well-Known Member
First Name
Michael
Joined
May 12, 2020
Threads
10
Messages
379
Reaction score
526
Location
Port Dover, Ontario, Canada
Vehicle(s)
2019 Jeep Wrangler Unlimited Rubicon
Occupation
GM, P.Log, CITT, 310T
You can differ all you want, but you’re still wrong. The ZF8 adapts to itself - clutch wear levels, fluid viscosity, etc. it does not adapt to it’s drivers’ long term habits.
Technically you are correct. The transmission itself does only adapt to its own internal conditions.
However, the entire electronic system, especially the TCM, does adapt to the driver's long term habits.
In today's electronically controlled vehicles, your foot does not tell the engine what it wants like the cable-to-the-carburetor methods of yesteryear. It actually tells the transmission, via the foot pedal potentiometer to the TCM, what it wants. The TCM asks the ECM if it can provide what the TCM wants, and the TCM also asks the drive train if it can handle what's about to come down the pipe. If the answer to all the requests are positive, your foot gets what it asks for. If any answers are negative a series of scenario evaluations ensue, and your foot's request is either granted by some other means, i.e. dropping a gear, or denied altogether.
Like every other computer system, algorithms and the numbers of times they are used are stored in hierarchy form from the most to the least so when you request something of the TCM it starts at the top of the list to grant the request. Habits put the most used algo's at the top of the list. Ergo the system "learns" what the driver wants.
My experience comes from long time use and management of automated class 8 highway equipment. Best way to screw up a new truck .... put a different driver in it every 12 hours.
 

Mikester86

Banned
Banned
Banned
First Name
Mike
Joined
Mar 5, 2020
Threads
59
Messages
2,055
Reaction score
5,156
Location
Michigan wishing I was on a trail...
Vehicle(s)
2022 JLR
MY 2020 JLUR 3.6 liter 8 speed auto does appear to hang out in 7th gear much longer then I would expect it to. Going 75 plus MPH on the freeway and heading down grade, I would expect it to shift into 8th. It will eventually, but not as quickly as I would expect it to.

There have been times I manually shifted into 8th, because it refused to on its own.
Sponsored

 
 



Top