FDII Low Range gear.

- George - · Mar 3, 2009

I tried the search tool but came up with too many threads.
My question i put forth to the teeming patriot masses is that
Does FDII achieve the low range by a transfer case or just simply from a low gear ratio? I'm pretty sure its from the gear ratio but i just wanted to make sure.
I was thinking of how to achieve this with a manual if possible to create it in a FDI.

Hitzy · Mar 3, 2009

Same CVT in FD1 and FD2, axle ratios are a little different.....6.12/8.13. No transfer case in these things in the normal sense, electonic coupler that locks it in 4x4.

- George - · Mar 3, 2009

so if you change the axle ratio in the manual, would it work?
Or, what if i change the 6th gear to a crawl ratio... hmmm.

APT · Mar 3, 2009

Changing axle ratios means front front and rear. This is fairly common for RWD-based manual transfer case vehicles, but parts cost about $600 with about equal amount of labor. I doubt there are any gears available with different ratios for our MKs. You cannot change the gear ratio of just one gear inside the trans. You got what you got.

jettore · Mar 3, 2009

I think the low range is an actual difference in the cvt2l transfer case vs the cvt2. The internal pulley sizes may be different allowing for the lower gear.

APT · Mar 3, 2009

There is no transfer case and the CVT gear ratios are the same (0.394-2.349_1) for all automatic MK's. The only mechanical difference is the axle ratio in the front and rear diff between what Jeep calls the CVT2 and CVT2L. hitzy is correct with the different axle ratios.

heckler · Mar 3, 2009

a quick search here brings me to this...

http://www.autofieldguide.com/articles/wip/0606wip05.html

"When the low-range mode is selected via a switch, a controller determines whether the vehicle is traveling at an acceptable rate of speed (the system can only be activated at speeds below 25 mph) and then engages a coupling mechanism, via specially developed software programming, to engage the secondary drive wheel while the CVT moves into a higher final drive ratio of up to 19:1"

says Matt Loddane, chief engineer for the Patriot and its platform-mate Jeep Compass

too many mis-information opinions instead of facts...

- George - · Mar 4, 2009

Thanks heckler,
good site!

Hitzy · Mar 4, 2009

heckler said:
a quick search here brings me to this...

http://www.autofieldguide.com/articles/wip/0606wip05.html

"When the low-range mode is selected via a switch, a controller determines whether the vehicle is traveling at an acceptable rate of speed (the system can only be activated at speeds below 25 mph) and then engages a coupling mechanism, via specially developed software programming, to engage the secondary drive wheel while the CVT moves into a higher final drive ratio of up to 19:1"

says Matt Loddane, chief engineer for the Patriot and its platform-mate Jeep Compass

too many mis-information opinions instead of facts...

This is how they calculate the 19:1 final drive (or Crawl if you prefer) ratio FYI

Transmission - 1st gear ratio (or lowest on CVT) x Final drive ratio = Crawl ratio

CVT2L w O/R Crawl Ratio: 2.349 x 8.135 = 19.11
T-355 5-speed: 3.77 x 4.12 = 15.53
CVT: 2.349 x 6.12 = 14.37

This info is on their website, and in all the brochures. Same CVT transmission in both FDI and FDII automatics.

heckler · Mar 4, 2009

Hitzy said:
This is how they calculate the 19:1 final drive (or Crawl if you prefer) ratio FYI

Transmission - 1st gear ratio (or lowest on CVT) x Final drive ratio = Crawl ratio

CVT2L w O/R Crawl Ratio: 2.349 x 8.135 = 19.11
T-355 5-speed: 3.77 x 4.12 = 15.53
CVT: 2.349 x 6.12 = 14.37

This info is on their website, and in all the brochures. Same CVT transmission in both FDI and FDII automatics.

facts and data. that i can appreciate.

- George - · Mar 4, 2009

Being in australia we dont get the FDII, only FDI.
I was wondering how I could replicate the FDII ratios in anyway, by replacement, customizing etc.
Engaging the secondary drive wheel, in the rear axle or Cvt? (bit new to me, and learning as i go...)

Aus Patriot · Mar 4, 2009

I would suggest this.

1. I think your coming to the conclusion that you would like to do a bit more than what the MK can do.
2. Your finding out that low range is needed to get to all those nice spots.

Am I getting warm or cold on this one?

If warm I'm going to say something that may not be popular.

Here goes.

If you need two cars in the family keep the Pat.
If you don't need two cars and are in a position sell it fast and don't spend any more money on it. Get a new KK crd if possible or look for a tidy 2nd hand CRD KJ.

If you need 2 x cars keep the MK give it to the wife and get your self a 2nd hand XJ. I've seen very nice XJ's for under 10k. Mods av like its xmas every day. The XJ will get you and your family to xyz where the Pat will never get you.

- George - · Mar 4, 2009

I think you could be right.

I would love an ol' banger to do up but not in a position to do so now,
But at the same time, I would like to do something that no one else has, but its not looking very good for me ATM.

(still got hope)
I even went to ARB and asked about the TJ bull bar, and the guy said he would give it a go fitting it on the Pat!! That'll be cool...

But one thing is for sure, I'm gonna push it as far as it can, Modding and driving!! (as long as I have a mate with a winch or snatch strap!!)

APT · Mar 4, 2009

CVT Article said:
"When the low-range mode is selected via a switch, a controller determines whether the vehicle is traveling at an acceptable rate of speed (the system can only be activated at speeds below 25 mph) and then engages a coupling mechanism, via specially developed software programming, to engage the secondary drive wheel while the CVT moves into a higher final drive ratio of up to 19:1"

[quote heckler]too many mis-information opinions instead of facts...[/QUOTE]

Irony. Just picking on you, heckler!

The whole article sounds more like marketing and opinion than fact. In the context of the article, pulling the 4x4 T-handle routes power to the rear axle. That's the only "secondary drive wheel" available on MKs and it has nothing to do with FDII specifically. And " which is more than enough to traverse just about any dusty trail or rough terrain" is clearly opinion.

To follow Hitzy:

How they calculate the top gear ratio:

Transmission - 5th gear ratio (or highest on CVT) x axle ratio = final drive ratio

CVT2L w O/R Crawl Ratio: 0.394 x 8.135 = 2.81
T-355 5-speed: 0.72 (or 0.81 for '07/'08 4x4) x 4.12 = 2.97 (3.34 4x4)
CVT: 0.394 x 6.12 = 2.41

So, what the "Low Range Gear" that the FDII gives in improved crawl ratio, it takes away from the top gear. So, CVT2 vs. CVT2L at 70mph will have the engine turning 2100rpm vs. 2700rpm in the top gear ratio.

The article does clearly state "without a two-speed transfer case."

- George - · Mar 4, 2009

So is it all just in the gear ratios then.
Nothing mechanically different.
If i was to lower my first OR possibly last gear (6th, cause i really dont use it that much, can handle only 5th for top gear) i could theoretically achieve 'Crawl ratio?

APT · Mar 4, 2009

The (axle) gear is mechanical.

You cannot change any arbitrary gear in your transmission. However, if you say you never use 6th gear, then you could benefit by changing the axle ratio by whatever the percentage 5-6th gear is. Wow! Looks like 4-5-6 gears are very close. I see no need for 5th gear, 4th and 6th seem good enough. In fact, the 5-spd with the 2.4L petrol engine is wider. Anyway, you could theoretically change the axle ratio by 13%, start in 2nd gear for most on-road situations and keep 1st for off-roading. However, I am not aware of any replacement gears of our differentials.

Gear Ratio Primer

Tony1911 · Mar 5, 2009

APT said:
However, I am not aware of any replacement gears of our differentials.

Yet another aftermarket product there would be a market for but nobody makes, in other words.

Programming BLDs to work would be another interesting trick - low range and the lack of BLDs being the main issues with an FDI Patriots off-road ability. Unfortunately seems Chrysler wanted to ensure nobody could easily modify their Jeep (what an unheard of concept, right? :icon_rolleyes: ) by tying software features to VIN numbers. One would have to come up with the FDII software and change the VIN in the computers memory to one that would allow free modification (there's bound to be some testing VINs that are not limited to only FDI features or FDII features).

- George - · Mar 5, 2009

I'm sure there would be shops that could fabricate custom gears? Since I have a VW gearbox, that would be likely, but the rear axle ratios would be a bit tricky and maybe if you got spare cash...
??
Taking off in second, would require changing that ratio too, (as it is, only way is to take off is on a bit of a decline/downhill)

Would you really need to change the rear axle ratio? Wouldn't keeping first or 6th maybe for the crawl ratio work? Or would it interfere with the rear axle ratio?

(All very interesting..)

Tony1911 · Mar 5, 2009

George, APT is talking about differential gears.

In other words, the transmission would remain stock. The overall ratio is after all a combination of transmission ratios, axle ratios and even tires.

- George - · Mar 5, 2009

so, in a nutshell, change the required transmission gears, and the required axle ratios, and i could replicate the FDII?

FDII Low Range gear.

- George -

Hitzy

- George -

APT

jettore

APT

heckler

- George -

Hitzy

heckler

- George -

Aus Patriot

- George -

APT

- George -

APT

Tony1911

- George -

Tony1911

- George -

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