Eco Diesel Re-gear

[iddpaul]

Hoping to get some real-time experience / help.

Firstly let me say that I'm a believer in re-gearing and have had this done to several past builds.

I'm looking to add a 2.5" lift, 37"s and a re-gear to my Eco Diesel and I'm hoping that I can get some feedback from anyone who's already done this. The numbers are simple, to get close to manufacturer (33's/3:73), on 35's, 3:73 would work but 4:10 seems the best. For 37's if you calculate it the best ratio is 4:30 (Nitro used to offer these). So I know some folks say stay with the original 3:73 for 37's, but that's NOT my question.

Has anyone run an Eco Diesel on 37's with 4:10's (maybe not enough) or 4:56's (maybe too much). I'll have some weight on my rig and will be pulling a small teardrop (2800 lbs). I'm leaning towards 4:56 but DON'T want to over-gear and have my rpm's too high when on the open road.

Please let me know if anyone has some "real world" experience - THX.

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[grimmjeeper]

My real world experience is keeping 3.73 gears. I ran 35s starting when I picked it up from the dealer. That was just about perfect for me. Plenty of power and good freeway RPMs. With the Rubicon transfer case it crawls like a tractor in the rocks.

I swapped out to 37s this last spring. No regear. The difference is enough to notice but not enough for me personally to spend money on a regear. I run around 1,6xx RPM at 75 with my combo. I still crawl like a tractor in the rocks.

4.10s would get me back closer to the 3.73/35s combo I liked. It would bump me up to 18xx RPMs at 75 which is still good for the diesel.

4.56s would be, in my mind, too much gear for my tastes. It would put me up around 2000 RPM at 75. That's not too much for the diesel but it's putting you above what is optimal for highway cruising.

What it comes down to for me is the cost of the regear compared to the benefit. A regear isn't cheap. And changing from 3.73 to 4.10 isn't enough of a change to justify the cost. At the same time, 4.56 is more than I want. It would be good if I towed but I have an F250 for towing.

 

[Rangemaster]

I run 3.73’s on 37’s and mine is like a race car. Just pop in a monster pedal and that will fix the pedal lag on most jeeps.

 

[Ratbert]

Mine came with 37s and 4.63s (supply constraints on the spec'd 4.56s) from AEV. Great torque for rock crawling and cruises fine with the cruise set at 87mph.

 

[BDinTX]

I don’t know nothing about nothing but I remember seeing some speculation on here about 3.73 being too much for the diesel / 33” combo but they weren’t able to go with a lower gear ratio in these axles.

I can still scurtch my 37’s with the original gears. Sorry I’m not answering your question though.

 

[Tpsillos]

I ran 38's on my 4.10s(take-off gas rubi axles) and it was pretty identical to stock as far as the RPMs/Speed. The 40s are a little much for the 4.10s, ill most likely go 4.56 with some junkyard one tons in the near future.

 

[grimmjeeper]

I don’t know nothing about nothing but I remember seeing some speculation on here about 3.73 being too much for the diesel / 33” combo but they weren’t able to go with a lower gear ratio in these axles.

I can still scurtch my 37’s with the original gears. Sorry I’m not answering your question though.

3.73 is the tallest gear you can get in the front M210 axle.

My personal speculation is that if the front axle had 3.45s available, the diesel would have come with that ratio.

 

[BuffaloBill]

I don’t have have the exact combo you’re considering; I’m running 35s and 4.10. If we compare figures using 33, 35, and 37” as the tire dimensions for simplicity, I’m geared about 3,6% deeper than stock, and do like it this way.

A lot of this comes down to personal preference, how much value one places on minimizing downshifts, etc. Mine does hold 8th gear against a mild grade and/or headwind better than stock (as you’d expect). I think that was my main objective for regearing. I occasionally pull an off-road camping trailer or an aluminum tilt bed car trailer with a subcompact Kubota. I don’t travel interstates often but when I have, have not found the rpm @ 75mph to be at all objectionable. The drivetrain still feels pretty relaxed to me.

If I did the math correctly, a 4,56 with 37s would be 9% deeper than stock, or about 5.4% deeper than my setup. If running in the 2k rpm range (for example) 5.4% of 2k is about another 100rpm. So given the additional wind drag from the lift & 37s, and the weight, maybe 4.56 would be the direction to go. But I’m sure the 37s with 4.10 would be fine too.

I’d never performed a gear swap before and wanted to gain that experience. I bought 4.10 gears from another member who’d geared his Rubicon (gas) deeper. Although I wound up not using the used front gear set, it still wasn’t a huge cost, and I appreciate the slightly deeper overall gearing every time I drive it.

 

[RafterCExplorations]

The correction formula for what gears you need to return to "stock" has always been "new tire height/old tire height x current axle ratio = needed axle ratio". Based on that a stock JLURD with 37s would require a 4.18 ratio, which obviously don't exist, so 4.10 would be "close enough". It may well be true that Jeep could not go lower using the same carrier in the stock axles, but i think the reasoning for the numerically lower axle ratio in the diesels is a product of low end torque combined with the 4:1 transfer case. That's a hell of a lot of torque through the drivetrain/axles at just off idle. As we owners know when you shift into low range, it feels like you could pull stumps all day. 35s with upgraded 4.10s might put undue stress on the axles, etc.

 

[RafterCExplorations]

In a better attempt to answer the OP's question, I'll go down this road...: My '08 Dodge/6.7 Cummins came with 3.73 gears. Its original tire size was about 31". I have been running larger tires (currently 35s) almost since it was new, and haven't, or even considered, re-gearing. BUT, repeat BUT, it is a 6 speed manual with a 5.??:1 first gear, and has been "tuned". It makes a LOT of power, and the manual allows me to drive it in the "power band" all the time, as well as manage temps (coolant, EGTs, etc) with the gears and my right foot. We have that capability with the manual mode of the auto trannys in our Jeeps, but I would guess that few do so. With EGTs not being normally monitored by us, I believe most don't realize the effect they have on all other temps downstream. As I have learned in my truck, just because I can hold 80 mph uphill in 6th gear at 1400 RPM, doesn't mean I should. The EGTs skyrocket, which can damage the engine internals, as well as rapidly increase coolant, oil and trans temps. In the truck, the solution is to downshift to 5th, let the engine RPMS climb to about 1800, and watch all those temps drop. Relative to Jeep gearing, we can all "drop a gear" in manual mode, and see the effect, AND still have the power we want on those grades, with or without trailers, etc.

 

[Adv_aw8s]

I have a 21 JLURD and live in Colorado. I ran 37's with stock gearing for about 10k miles. It was not bad but it lived in 7th alot. When we had our rooftop tent on top with a little bit of head wind I could really tell I needed more gearing. It would downshift to 6th pretty frequently. I regeared to 4.56's. we since sold the tent and now tow a Boreas offroad trailer that weighs about 2600-2700 loaded. I think the gearing is perfect and I should've went to 4.56's sooner. I'm seeing 18-20mpg towing and about 22mpg empty. I will say offroad in 4low 1st gear is only used for the toughest sections. I typically lock it in 2nd for steep climbs like in Moab or sand hollow. I think 4.56's paired with 37's is damn near perfect especially if you are towing.

 

[av8or]

A friend of mine runs 4.56s and 37s on his gladiator diesel and swears by them.
It’s all I got…I have gasser.

 

[Roky]

Hoping to get some real-time experience / help.

Firstly let me say that I'm a believer in re-gearing and have had this done to several past builds.

I'm looking to add a 2.5" lift, 37"s and a re-gear to my Eco Diesel and I'm hoping that I can get some feedback from anyone who's already done this. The numbers are simple, to get close to manufacturer (33's/3:73), on 35's, 3:73 would work but 4:10 seems the best. For 37's if you calculate it the best ratio is 4:30 (Nitro used to offer these). So I know some folks say stay with the original 3:73 for 37's, but that's NOT my question.

Has anyone run an Eco Diesel on 37's with 4:10's (maybe not enough) or 4:56's (maybe too much). I'll have some weight on my rig and will be pulling a small teardrop (2800 lbs). I'm leaning towards 4:56 but DON'T want to over-gear and have my rpm's too high when on the open road.

Please let me know if anyone has some "real world" experience - THX.

Hi Paul, did you get a new rig ?

 

[rick6633]

I have a 2022 AEV JLURD. I have 37’s and 4.63’s also. I just finished the rubicon trail in July and love the way mine performs on and off road. I I also just spent the month of September traveling and towing my Boreas XT teardrop style off road trailer in Colorado. About the same weight as yours. The jeep performed amazingly and average fuel economy for me was 19 miles per gallon over 22 fuel stops. While on the trip I completed 4 badge of honor trails and 6 other non badge of honor trails in different parts of the state. I’m completely happy with the gear performance on and off road. Side note: On the highway while towing I usually keep the speeds between 65-75 depending on the highway speed limits.

 

[iddpaul]

I have a 21 JLURD and live in Colorado. I ran 37's with stock gearing for about 10k miles. It was not bad but it lived in 7th alot. When we had our rooftop tent on top with a little bit of head wind I could really tell I needed more gearing. It would downshift to 6th pretty frequently. I regeared to 4.56's. we since sold the tent and now tow a Boreas offroad trailer that weighs about 2600-2700 loaded. I think the gearing is perfect and I should've went to 4.56's sooner. I'm seeing 18-20mpg towing and about 22mpg empty. I will say offroad in 4low 1st gear is only used for the toughest sections. I typically lock it in 2nd for steep climbs like in Moab or sand hollow. I think 4.56's paired with 37's is damn near perfect especially if you are towing.

Thx, that's perfect, just what I wanted to hear!

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