Street Re-gear advice

[Anthi4078]

Hey I’m thinking about re gearing my truck to get a little more umph when you push the pedal and I’m torn between 3.55s and 3.73s. My trucks a 4.0 5 speed and I run 235/75/15s which I think are like 29s. I don’t plan on changing my tire size to anything bigger and the truck gets driven daily with a mix of city and highway. What do y’all think is the best option to make it feel a little more sporty but not be wound out and sucking back the gas on the highway?

Thanks, Andre

[Pete M]

you'll be happy with either of those ratios.   when my dana 35 blew up I found a 44 with 3.55s and that little bump (had 30s, which are about the same size as 235s) really put a smile on my face   (until the peugeot blew up a couple months later).  the 2.5L/5-speed got factory 4.10s, so 3.73s aren't too much either. 

[cruiser54]

3.55s are way easier to find, but you will like either one. 

[gogmorgo]

My 4.0/ax15 ZJ gets around just fine with 3.55’s on 31’s, but any time I’ve put a trailer behind it I’ve wished I had a little deeper gears, even when I just had 235/75R15 tires.

I don’t remember where the carrier break is on the 44, but you’ll need a new carrier for your D30 to run 3.73 gears. Not a huge expense but still something to consider if budget’s a concern.

It shouldn’t be a huge jump in RPM on the highway. Maybe 150rpm higher at 75mph for 3.73’s over 3.55’s.

[derf]

On 7/16/2023 at 8:41 PM, gogmorgo said:

My 4.0/ax15 ZJ gets around just fine with 3.55’s on 31’s, but any time I’ve put a trailer behind it I’ve wished I had a little deeper gears, even when I just had 235/75R15 tires.

I don’t remember where the carrier break is on the 44, but you’ll need a new carrier for your D30 to run 3.73 gears. Not a huge expense but still something to consider if budget’s a concern.

It shouldn’t be a huge jump in RPM on the highway. Maybe 150rpm higher at 75mph for 3.73’s over 3.55’s.

Carrier break on a 44 is 3.73 and down.

 

If I were building a stock-ish MJ I'd do 3.73s and TrueTracs front and rear.  And at least 30x9.5/15 tires.

[Anthi4078]

Well thanks for your help everyone, I found a good deal on some 3.55 gears and not having to swap any carriers or anything sounds good to me so 3.55 it is for now at least. 

[Pete M]

used gears?  or new?

[Anthi4078]

19 hours ago, Pete M said:

used gears?  or new?

Used.  Found a whole axle on marketplace for $60 so I’ll probably end up just swapping the axle since it’s got newer ball joints and it’s non CAD. 

[Pete M]

careful with used gears.  they can be quite noisy, even if set up correctly.   have you ever installed gears?

[gogmorgo]

Yeah, used gears don’t always like taking a new wear pattern. You’d want to know how much backlash was in the old setup and aim to get it as close as possible to that instead of setting them up as though they’re new. 
A complete axle is a bit less to manage than used gears. I’d still go through and replace all bearings and seals in the used axle, you’d be most of the way to that anyway just regearing the existing axle.