Using manual shifter to get into 8th gear?

[RubiGrey]

Hey folks,

Just a bit of background information. I've upgraded my jeep and it's gotten a little heavy:
- 35" tires
- Roof rack
- Rooftop tent
- Mopar lift
- Steel rock sliders
- Stock Rubicon gears
- V6

I know adding the rooftop tent makes it heavier and even less aero dynamic.

I am getting around 19L/100km (12.37 MPG) and I rarely see 7th gear and never see 8th gear.

My Jeep does have the manual mode so you can manually shift it into 8th gear.

So my question is, will I see any improvement in fuel economy or see less wear and tear on my gears if I shift into 8th on the highway or on long stretches without traffic lights ?

Thank you!

Sponsored

 

[Tncdrew]

I'd think by manually forcing the trans into 8th (a ratio that it doesn't seem to want to shift to on its own), may put that V6 into a lugging situation. Unfortunately those aren't the most torque rich (at lower rpm) engines, and your situation may require higher rpms....
Not sure of I'm explaining that clearly? ? ?

 

[rohdawg]

@RubiGrey Have you calibrated your speedo for the larger tires?

If not, that will impact what you’re seeing for gas mileage and the shift points for your transmission.

 

[RubiGrey]

I'd think by manually forcing the trans into 8th (a ratio that it doesn't seem to want to shift to on its own), may put that V6 into a lugging situation. Unfortunately those aren't the most torque rich (at lower rpm) engines, and your situation may require higher rpms....
Not sure of I'm explaining that clearly? ? ?

I think so? Obviously if I manually shift it to 8th I won't get any power, I can floor the gas but it aint gaining much speed. This is for situations where I am already at speed.

 

[RubiGrey]

@RubiGrey Have you calibrated your speedo for the larger tires?

If not, that will impact what you’re seeing for gas mileage and the shift points for your transmission.

I did at one point, but I was having other issues and the dealer quickly pointed out the device I had plugged into my OBD2 port .. So I took it out so they could troubleshoot under warranty.

 

[rohdawg]

I did at one point, but I was having other issues and the dealer quickly pointed out the device I had plugged into my OBD2 port .. So I took it out so they could troubleshoot under warranty.

I have a ‘21 JLUR that’s decked out similarly to what you describe, minus the rock sliders. 35” BFG KO2s and used the Tazer to adjust.
I have no problem getting through the gears and see 7th and 8th where you’d expect to.

Adjusting for the correct tire size should help you out quite a bit.

 

[Ratbert]

As others have said: adjust your rig for the correct tire size.

 

[vaJLUR]

Higher load/lower rpm is generally going to give you the opposite of any increased efficiency..
The only real way to monitor this kind of effect is to monitor your spark tables while doing this.

 

[Tncdrew]

And a sidenote...
If you've never played around with this awesome calculator made by one of the forum members, check it out!
Very handy! ?

http://www.grimmjeeper.com/gears.html

 

[jeepoch]

@RubiGrey,

Is your Jeep a Rubi or something else? What gears do you currently have?

In my experience the 8-Speed Auto does a wonderful job at adjusting for the 35's. It has the ability to 'learn' your overdrive habits by seeing that you request 8th gear often.

When I lifted my 2019 Sport 3.6L 2-Door and installed 35's, I too lost 8th gear (at least automatic selection). It remained that way until manually selecting it wherever I thought it was beneficial. After doing this enough, the trans controller now routinely selects 8th gear way more frequently. Still nowhere near as often as when I had the 31.5" stock Michelin's but enough now to where I'm no longer surprised when I see 'D8' on my EVIC display.

Still, I use the AutoStick feature a lot and manually shift gears frequently, especially downshifting. I do find that I need to manually shift into 8th occasionally but certainly not as frequently as when the 35's were first installed.

For me, running on the stock 3.45 gears has never been an issue. This tranny seems like it was almost designed for the 35's all along.

For the MT6 jocks, they certainly have to pay more particular attention to their gearing on tire size changes. With this ZF8 however, I've completely removed all thought of performing a gear swap.

I do off-road frequently living here around the Colorado Front Range and get good all-purpose performance for my daily driver. Close to 23 mpg with a highway/city mix. Sometimes as high as 25 mpg if I stay off I-25 in my travels. But that's where 8th is really needed the most, on the freeway at the posted 75 mph speed range.

Driving in the foothills also introduces more manual shifting opportunities and I'm almost never in 'Drive' while in 4Lo, so I'm not your typical auto-pilot type of driver. I certainly do enjoy a balanced mix of selection. Manual when I'm more aggressive and lazy when in stop and crawl I-25 snarl when anywhere near downtown Denver.

So 8th is just another gear. Whether the tranny selects it or I do, it's there when I want it.

Happy travels,
Jay

 

[RubiGrey]

@RubiGrey,

Is your Jeep a Rubi or something else? What gears do you currently have?

In my experience the 8-Speed Auto does a wonderful job at adjusting for the 35's. It has the ability to 'learn' your overdrive habits by seeing that you request 8th gear often.

When I lifted my 2019 Sport 3.6L 2-Door and installed 35's, I too lost 8th gear (at least automatic selection). It remained that way until manually selecting it wherever I thought it was beneficial. After doing this enough, the trans controller now routinely selects 8th gear way more frequently. Still nowhere near as often as when I had the 31.5" stock Michelin's but enough now to where I'm no longer surprised when I see 'D8' on my EVIC display.

Still, I use the AutoStick feature a lot and manually shift gears frequently, especially downshifting. I do find that I need to manually shift into 8th occasionally but certainly not as frequently as when the 35's were first installed.

For me, running on the stock 3.45 gears has never been an issue. This tranny seems like it was almost designed for the 35's all along.

For the MT6 jocks, they certainly have to pay more particular attention to their gearing on tire size changes. With this ZF8 however, I've completely removed all thought of performing a gear swap.

I do off-road frequently living here around the Colorado Front Range and get good all-purpose performance for my daily driver. Close to 23 mpg with a highway/city mix. Sometimes as high as 25 mpg if I stay off I-25 in my travels. But that's where 8th is really needed the most, on the freeway at the posted 75 mph speed range.

Driving in the foothills also introduces more manual shifting opportunities and I'm almost never in 'Drive' while in 4Lo, so I'm not your typical auto-pilot type of driver. I certainly do enjoy a balanced mix of selection. Manual when I'm more aggressive and lazy when in stop and crawl I-25 snarl when anywhere near downtown Denver.

So 8th is just another gear. Whether the tranny selects it or I do, it's there when I want it.

Happy travels,
Jay

Glad to see you’ve had success with this method.

I’m currently running 35x12.5 KO2’s and I’m in a 4-door Rubicon, so 4.10’s

the added height and weight of the rooftop tent doesn’t help either.

 

[58Willys]

I’m not a huge fan of computer controlled vehicle; but if your computer won’t shift to a higher gear over riding it is a bad idea, you will be lugging the motor and not doing it any favors. You need to re-gear.

 

[tomk62]

+1 on making sure your Jeep still has the correct tire size programmed.

 

[grimmjeeper]

Two things keep your transmission from shifting into 8th. First, like everyone else says, make sure your computer is set for the right tire size. Second, if it still doesn't shift into 8th, you need shorter (higher number) axle gears. Swapping out axle gears is a significant investment so it's not something to do lightly.

Manually shifting into 8th takes your engine out of its power band and lugs the engine. You get less power and worse fuel economy. The V6 needs to stay above 2,000 RPM to be in its happy place. On the freeway, cruising above 2,200 or more is a good place to be.

 

[Vinman]

When it comes to gear selection and fuel economy this is my rule of thumb.
Select the gear that allows the least amount of throttle pedal input, ie if 6th gear the pedal is pressed 1/4” from idle to maintain desired speed then you switch to 7th gear if the pedal is pressed less than 1/4” you’ll get better fuel economy, if it requires more than 1/4” you get worse fuel economy. Ignore the engine RPM’s.
I think you’ll find “forcing” the transmission into a higher gear by manually selecting it, you’ll need more throttle input to maintain the same speed which will result in less fuel economy.

Sponsored