Regearing from 3.73 to 4.56 and locker advice

DuneSeeker

DuneSeeker

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Aug 29, 2021
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Dubai
Hi Everyone, Nice to join this group.

I have a 2005 Manual Transmission TJ Sport with a Dana 30 in the front and Dana 44 in the rear - currently running stock 3.73 gears.
I am on 32" Cooper STT Pros which I deflate to 7psi when riding in the desert (and no - they have never popped off - TJs are light)

I do a lot of big dune desert driving where you need speed and most often I have to be in 4 Low running 4th and 5th gears on the big dunes.

I realize that I am putting excess strain on my drive train and have decided to regear to 4.56 so that I can stay in 4 Hi in the big dunes and not have to resort to 4 Low.

My questions are as follows:

1. Would 4.56 be the right gear ratio for me on 32" tires to maximize the power output from my 4.0 engine?

2. Do I need to change the carrier on the front or rear when I do this gear change?

3. I also want to install air lockers while Im doing the regearing and would like to ask whether the lockers and carrier change are going to be a problem in terms of fitment.

thank you very much!

This video (courtesy of a buddy of mine) will give you an idea of the kind of drives and speeds we do:
 
Welcome to the forum!

So im doing this exact gear swap in a few days, I think 4.56 would be a perfect ratio for you.

Yes, you will have to change your carriers at the same time

If you're doing air lockers they actually REPLACE the carrier so you won't need carriers if you get air lockers instead, you do still have to make sure that the locker you get will fit the 4.56 gears,

have fun! that dune riding looks gnarly

Edit: actually I just remembered you WON'T have to get a new carrier for the front dana 30
 
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Thanks guys - really appreciate it. I had no idea that the air lockers replace the carriers - that is great to know.
I got a reply from the guys at Northridge 4x4 and they are telling me to get this "thick" gear set for the rear.
But is that even necessary if I am getting air lockers?

This is the rear locker and front locker they have selected for me.
 
DuneSeeker said:
Thanks guys - really appreciate it. I had no idea that the air lockers replace the carriers - that is great to know.
I got a reply from the guys at Northridge 4x4 and they are telling me to get this "thick" gear set for the rear.
But is that even necessary if I am getting air lockers?

This is the rear locker and front locker they have selected for me.
Click to expand...
You could go with either option. You can buy a 3.73 and down carrier and install thick gears or a 3.92 and up carrier and install standard gears.

There will be no noticeable performance or cost difference between the two.

If you're buying new carriers and gears, I would just go with a 3.92 and up carrier and standard gears to save a tiny bit of unsprung weight and rotating mass.

With that linked rear locker you want standard gears, not thick.
 
Also, for dune riding exclusively, you might also look into gear driven limited slips like the Truetrac differential. They have very good handling manners and lock/unlock instantaneously. They don't have 100% of the traction ability a true locker has, but are very popular for off-road racing and high speed use.

In your case I would also strongly consider chromoly shafts front and rear. Revolution Gear and Axle makes a great US-made set for front and rear.
 
No need for thick gears when you're replacing the carrier since you can order it to match the new lower R&P ratio. Thick gears were developed for when you want continue using an existing locker made for higher ratios like 3.73 but you want to regear to a ratio that is lower than the locker was designed for.

Thick gears means the ring gear is made thicker so its teeth can properly engage the smaller diameter of a lower ratio pinion gear that would otherwise be too small for the ring gear to reach and fully engage.

Before there were thick gear sets the carrier would have to be changed so it would position the new ring gear close enough to fully engage the smaller diameter (lower ratio) pinion gear.
 
thekidwithquestions said:
Welcome to the forum!

So im doing this exact gear swap in a few days, I think 4.56 would be a perfect ratio for you.

Yes, you will have to change your carriers at the same time

If you're doing air lockers they actually REPLACE the carrier so you won't need carriers if you get air lockers instead, you do still have to make sure that the locker you get will fit the 4.56 gears,

have fun! that dune riding looks gnarly

Edit: actually I just remembered you WON'T have to get a new carrier for the front dana 30
Click to expand...
Thanks - let me know how the new gears turn out in your TJ !
 
So I did some calculations on this regearing (see attached screenshot). These numbers are based on 1 RPM of input and for a 2005 TJ Sport with the NSG 370 manual transmission. Please let me know if I have made any errors in these calculations.

My most useful and best gears in the big dunes are 3rd and 4th (4Low) which correspond to 17.5x and 12.7x. In 4Hi 2nd gear (9.7x) is useless and you cant climb the big dunes. 1st is too slow but a useful gear to gain momentum. But in 4 Low shes a dream and is able to do anything. Just a reminder - I have 32" tires and a 3.73 gear ratio.

If I regear to 4.56, my 2nd gear in 4Hi is going to 11.9x which is great but 3rd would not be usable and I would have to stay in 2nd for most of the drive. (1st is too deep to get any speed and would only be used in small technical dunes).

The purpose of this regearing was so that I can avoid relying on 4 low so often because I was concerned about wear on my drive train.

However I am wondering whether that is really the case? At the end of the day it seems like I am putting a similar amount of torque through the drive train whether I am in 2nd Gear (4Hi) or 4th Gear (4 Low). Both front and rear are locked whether it is in 4Hi or 4Low so I am not understanding where the additional strain really is to the drive train based on the transfer case setting.

I also realize that Jeep advises not to drive over 10mph but I have been using 4 low in TJs for 10+ years in the dunes. However, I have broken one front drive shaft and one rear in those 10 years. I have an SYE kit and adjustable control arms now.

I drive this jeep almost every weekend 6 months of the year so it amounts to a fair bit of desert driving. I do fear breaking my transfer case, but that's a fear that has not come true (luckily) in the 10+ years Ive been desert driving in TJs. Is that a real risk if I continue using 4 low?

Sorry for the long post. I've been dreaming about gear ratios.

Screen Shot 2021-08-31 at 10.27.48 PM.png
 
Great to see somebody really doing all the math. Overall I think regearing will reduce the driveshaft loads and really reduce the stress on the transfer case planetary set for you specifically. You know what it takes to fix the driveshaft and NP231 cases are pretty cheap so there's that. The downside of regearing is your gear spacing is going to suck as you've seen. I'm really in favor of upgrading when you get tired of fixing stuff you break. You might just thrash the heck out of that transfer case, change the oil often and when it catches fire or you get tired of fixing your driveshafts regear.
 
Steel City 06 said:
Also, for dune riding exclusively, you might also look into gear driven limited slips like the Truetrac differential. They have very good handling manners and lock/unlock instantaneously. They don't have 100% of the traction ability a true locker has, but are very popular for off-road racing and high speed use.

In your case I would also strongly consider chromoly shafts front and rear. Revolution Gear and Axle makes a great US-made set for front and rear.
Click to expand...
Maybe he would prefer UEA made :ROFLMAO:
 
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Reactions: Steel City 06
I’ve got the 5 speed with 4.56 gears and 32’s. It’s great and you will love the power!
 
Watching the sand dunes video somehow reminds me of watching surfing. Looks a bit sketchy for my tastes. I'll stick to .00000001 mph rock crawling. :D
 
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