My dilemma

[fiatslug87]

So I have an ‘89 2WD with a D44 and 3.55 gears and an ‘88 4WD with a D35 and 3.07 gears both 4.0L, my plan is to swap axles. The ‘89 is my beater; haul stuff to the dump, Home Depot runs, etc. while the ‘88 is my project on 31’s mostly used in freeway/city driving in California so good weather. Should I just regear the front to 3.55 or do both to 4.10? Like I said not much 4x4 action and I don’t need to spin the tires, I’m way too old for that. Thanks.

[derf]

I'm assuming the 88 with the 31s has the automatic.

 

If so, 4.10s would put you around 2,600 RPM at 75 on the freeway.  That's about 100 more than the stock 3.55s with 215/75R15.  That's about where I'd want to be.

[fiatslug87]

The ‘88 has an AX-15. I aways forget some details 

[89 MJ]

1 hour ago, derf said:

I'm assuming the 88 with the 31s has the automatic.

 

If so, 4.10s would put you around 2,600 RPM at 75 on the freeway.  That's about 100 more than the stock 3.55s with 215/75R15.  That's about where I'd want to be.

Being that the 88 currently has 3.07s and based on his signature, looks like the 88 has a 5 speed. 
 

 

Personally, I think 4.10s are a lot of gear for a truck that lives on the street. If I were to do my truck again, I’d probably run 3.73s with 4.10s. I’d probably even try the 3.55s before regearing at all. With 4.10s, I find a lot of speeds that I do are right between gears. 30 mph feels between 3rd and 4th and 45 feels between 4th and 5th. Not to mention, my 1-2 shift is usually in the middle of an intersection, which I don’t care for. 

[derf]

So stock 215/75R15 with 3.08s runs just under 2300 RPM at 75.

 

3.55s with 31s will put you around 2400.

3.73s would be around 2500.

4.10s gets you just under 2800.

 

I'm planning my long bed build with 31s and an AX15 and I'll be doing 3.55s.  It will be an all around driver that I can do road trips in.

 

For my chief with the AX15 and 35s, I'll have 4.56, which will run 2700 at 75 but it's going to be a rock crawler that doesn't see much highway time.

[Pete M]

I never want to own a Jeep with less than 4.10s   (unless keeping it stock is the priority)

 

I even have 4.10s in my diesel Liberty

[pizzaman09]

I recently did a highway drive towing a trailer with stock 3.08 gears on 225 75 R15 tires and an AX-15.  I decided to leave it in 4th and set the cruise control.  The fuel mileage was atrocious but at least I wasn't at full throttle forever.  I eventually shifted up into 5th, but basically needed to run flat out most of the time to maintain 70mph.  I can totally understand wanting steeper rear gears, really I want a gear splitter or an extra overdrive unit.

[neohic]

My vote would be for 4.10s if you had an automatic. 4.0s don’t mind reving a little more but I agree that 3.55s and a stick feels about right on 31s.

[Pete M]

don't fear the extra RPMs.  the engine doesn't care and your fuel economy will be roughly the same.  once you get used to the change, you'll never want to go back  

[watchamakalit]

4.10's and 31's for the win. I love mine. Definitely the way to go. 

[Gjeep]

My 92 was a daily commuter for years -- 4.0, AX-15 4x4, swapped in 3.55 axles early on and loved it. Felt right.