Looking to re-gear and hoping for suggestions.

[TerryMason]

I'm looking to change out the 3.73 gears in my 2005 Jeep TJ. It has the 4.0L and the 42RLE auto trans. I currently have 33s, and may upgrade to 35s in the future (but this isn't set in stone).

I've got a dana 30 with a lunchbox locker in the front, and a ford 8.8 with a factory limited slip in the rear.

I've been doing research, and I've found a couple of sites that say 5.13s are where I want to be, but others say 4.88s would be ideal. Any opinions on what would work best for my mostly street, offroad twice a year Jeep?

 

[superj]

32s with 4.10 is awrsome on our 4.0/42rle.

I would bet 4.88s make 33s spin easily, like the 4.10 does on the 32s. Maybe even easier.

For 35s though, i would get the 5.13

 

[JPNinPA]

How fast do you need to go on the highway. Or in general? You could calculate engine RPM to rear wheel rpm through the gears. Running 2400-2700 rpm is a sweet spot for power and efficiency on the highway.
Too low and your screaming down the highway. Too tall and you are low in the engines power. Area and lugging the engine.


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[TerryMason]

I've been running 3.73s and 33 inch tires for so long that I grew used to how much the engine lugs. I am doing 60mph or so at about 1600 RPM - I shake my fist at the tractor trailers as they blow by me. I've needed gears for a while.

I used this site to figure out my new speeds and RPMs, it's a great tool.

Gear Ratio Calculator

3.73 (current) gears on the left, and 4.88 on the right. Looks like this would put me right where I'd want to be.

I've ordered 4.88 gears, bearings, etc for the rear axle. I'll get that one done then move to the Dana 30 front.

 

[JPNinPA]

Is the 4.88 with 33’s or 35s?

Bearing Wear: Lugging puts high pressure on crankshaft bearings while they are receiving low oil pressure, potentially leading to premature bearing failure.
Internal Damage: Continued, severe lugging can lead to damage to piston rings, connecting rods, and can even crack pistons.


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[JPNinPA]

My 05 manual unlimited with the stock tire @72 mph 2032rpm
With 33’s @72 mph 1847
4:11 would correct for 33’s
4:56 correct for 35’s

Currently when on the flat its ok
But hit any hill I’m downshifting to maintain 65-68mph or passing.


Funny now thst you know bow to… you’re hooked.

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