Gear Ratio for 2012 CRD 2.8L JKU

[uwiik]

Originally Posted by Paul-JK

Not sure if the specs are the same in Jakarta as they are here but as far as I'm aware the CRD auto comes with 3.73 ratios, not 3.21. The 07 models all had 4.1's and then they switched to 3.21 for manuals and 3.73 for autos as far as I know (and the Rubicons have always had 4.1). I have the MY10 CRD auto and mine certainly came with 3.73's.

I'm also fairly sure that the MY11 & MY12's have a mercedes 5 speed box (with tip-tronic gear select) rather than the older 545RFE Chrylser box that MY07-MY10 CRD autos had. Don't know if there was much difference in gear ratios between them though.

I'm surprised you felt such a difference with the 33's. I run 33's on mine and didn't notice that much of a difference from stock.

Pretty sure we have the same spec. My key fob have AU designation on the sticker, my new vehicle sticker have AU designation too....Hey we're neighbour, remember??

I got 3.21 ratio from the Chrysler - Jeep brochure, it clearly stated 3.21 axle ratio on the brochure.

I have tiptronic on my box and I tried cruising at 60kmh with manual override at 4 and full auto, I was cruising at 1300 ish, definitely spinning higher than 545RFE on CRD would. I think 2012 CRD comes with mercedes auto.

I felt it lacks gearing even with stock tyre, it has good power above 2000, but below that it was just a pig and going to the wrong gear sometimes. Now I got 33 Toyo, which is like one of the heaviest, and planning to add steel bumpers and winch, the difference can really be felt especially with 3.21 gearing I am having. It is actually a logical change for the designer to decide to re gear to 3.21 for 2012 due to different mercedes trans, but in real world application I don't think it just work like that.

Decision decision ...

[Paul-JK]

Originally Posted by uwiik

I got 3.21 ratio from the Chrysler - Jeep brochure, it clearly stated 3.21 axle ratio on the brochure.

Having 3.21 ratios would certainly explain the sluggishness I suppose.

I don't know a great deal about re-gearing as it's not something I've considered doing but based on how mine drives with 3.73's on 33's I don't think you'd need any more that 4.1's. 4.56 or 4.88 are probably better suited to 35's.

Also, have you tried getting an AEV Procal unit (assuming they work for the MY11/MY12's)? You can change a few parameters with them so they're quite useful. They can re-calibrate your speedo to suit the bigger tyres and it also alters the shift pattern of the auto box to account for the bigger tyres as well (or at least it does with the 545RFE).

[craigperth]

Becreful, I dont believe PROCAL or SUPERCHIPS can reprogram gears in the 2011 and upwards... I believe new gears will cause an engine light as the sensors will have wrong readings... speak to PROCAL or SUPERCHIPS first.

[samft]

4.88's are good on my 2010 CRD auto with 35's
4.11 would be sluggish i think

[uwiik]

Originally Posted by Paul-JK

Having 3.21 ratios would certainly explain the sluggishness I suppose.

I don't know a great deal about re-gearing as it's not something I've considered doing but based on how mine drives with 3.73's on 33's I don't think you'd need any more that 4.1's. 4.56 or 4.88 are probably better suited to 35's.

Also, have you tried getting an AEV Procal unit (assuming they work for the MY11/MY12's)? You can change a few parameters with them so they're quite useful. They can re-calibrate your speedo to suit the bigger tyres and it also alters the shift pattern of the auto box to account for the bigger tyres as well (or at least it does with the 545RFE).

I am planning to go 4.11 right now due to the fact that I am going to fit steel bumpers and whatnot soon.

Regarding the procal AEV, we can have entirely different discussion regarding that.

I bought pre 2012 procal not knowing that they have 2012 procal, then used the one I just bought to adjust my tire size and shift point, for some reason I was doubting that it worked because even though it honks twice after every program, the delay was just too quick to be believable, the horn would honk the millisecond I connect the procal to the OBD port, like there was nothing and it just honks, then I decided to reset all parameter store the older version of the procal and buy a new one with 2012 sticker on the box, funny thing is the newer 2012 procal does not really work on my 2012 CRD auto, it honks twice after program, but always followed with red led blinking on my dash which according to AEV, is an error code. I then claimed warranty and get another brand new procal with 2012 sticker on it, tried it again and getting the same result. I tried to drive anyway with shift point revised to 4.11 gearing, initially it felt quicker but then the computer threw check engine light and sent my car to limp mode. Tried to clear DTC code with the 2012 procal to no result, no honks nothing, just red light blinking indicating an error, tried parameter reset, same result. I almost gave up and wanting to get the dealer to reset the light, but then I decided to try my previous pre 2012 procal and Voila! It actually worked, my check engine light went off and my jeep went back to normal driving....

Now I am very confused, which procal should I use for 2012 Auto CRD? Is there any way to physically tell whether my older procal works or not on my 2012 CRD?

[uwiik]

Originally Posted by craigperth

Becreful, I dont believe PROCAL or SUPERCHIPS can reprogram gears in the 2011 and upwards... I believe new gears will cause an engine light as the sensors will have wrong readings... speak to PROCAL or SUPERCHIPS first.

they have 2012 version of procal, but read my story below about two of my procals.

[uwiik]

Originally Posted by samft

4.88's are good on my 2010 CRD auto with 35's
4.11 would be sluggish i think

With Chrysler 545RFE yes I believe 4.88 is the way to go, but I believe 2012 CRD comes with 5 speed mercedes same as the pentastar because I have tiptronic on my auto box and I am running 1300 ish RPM at 60kph @4th gear.