Can I regear to 3.55?

[Libertard2k6]

I have an 06 Liberty 65th anniversary edition, my question is can I regear to 3.55 and would it improve mpg by much? I don’t do a lot of towing and mainly just use it for daily driving in rural Indiana

 

[lfhoward]

I would advise against that. Running a larger tire size would essentially accomplish the same goal and I can say from experience (running a 30.5” tire) that gas mileage has NOT improved. The engine struggles in 4th gear on hills that would normally be no problem with stock gearing.

 

[Libertard2k6]

I would advise against that. Running a larger tire size would essentially accomplish the same goal and I can say from experience (running a 30.5” tire) that gas mileage has NOT improved. The engine struggles in 4th gear on hills that would normally be no problem with stock gearing.

Large tire would improve my fuel economy?

 

[lfhoward]

Large tire would improve my fuel economy?

More distance covered per revolution…

But also more weight.

 

[Libertard2k6]

More distance covered per revolution…

But also more weight.

Ah, fair enough, I guess I never thought about it that way

 

[tommudd]

Large tire would improve my fuel economy?

Larger tires you need to run a lower gear like 4.10s
running a 3.55 on an automatic would be operating the engine in a lower RPM than what it was designed to run

 

[Enorton5]

I'm about to go from running 245/75/r16 to 265/75/r16's so I'm preparing to regear and from what I've read you can not just change out the ring and pinion in the front diff of a 3.7 06 gasser, but that you have to change out the entire axle. That said would the front axle from a 2.4 gasser 02-05 be a perfect swap to the 06 3.7 kj.

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[nbas]

You need to regear front & rear diff. 265/75R16 is too large, as far as I know it will not fit under normal circumstances. 265/70R16 would fit instead of 245/75R16. I am running on 245/75R16 and I am very happy since I regeared to 4.10 (see my signature). i prefer 245/75R16 as it sits better on my stock rims, it has the same profile (compared to 265/70R16) without being very wide...

 

[Enorton5]

I understand that you need to regear the front and back which is the basics so I felt I need not have to type it, and you still did not answer my question. Yes, a 265/75/r16 will not fit with no lift, but I have the appropriate lift. I understand that you prefer a smaller tire, but I do not.

 

[lfhoward]

You’re asking if you can regear the front diff of your KJ or if you have to swap the whole front diff with one from a 4 cylinder KJ that is already geared to 4.10, correct? Ether way is fine. It tends to be easier to swap diffs rather than regear because a regear is labor intensive and typically costs a lot. 4 cylinder KJ gassers are getting harder to find, though. They were only made for a short time, and in low numbers.

Just some more regearing trivia for KK owners, if they read this thread. KK’s are a bit different:
- No KK’s came from the factory with 4.10 gearing, so a ring and pinion swap is needed with larger tires. (No diff swap option)
- KK’s can support 4.10, 4.56, or 4.88 gears. KJ’s can only go to 4.10.
- 4.10 is good for 31” tires, 4.56 for 32’s. We can’t typically run tires larger than that to make use of the 4.88 option.
- KK front diffs use the JK Wrangler Dana 30 ring and pinions, where as KJ front diffs use Dana 30-A gears only.
- KK’s and all but the earliest KJ’s have the Chrysler 8.25 rear diff. A few very early KJ’s came with a Dana 35 in the rear.

 

[nbas]

As far as I know, 265/75R16 will not fit even with a lift (I felt that I did not need to type it as you already have 245/75R16) under normal circumstances (I meant without further cutting...)
You can either change the front ring/pinion or swap a front diff from a 2.4 (what I did as I could not find front 4.10 ring/pinion in Greece)