ECODIESEL DIFF RE-GEARING

[grimmjeeper]

don’t get so hung up on “perfect”; it isn’t going to be the same for everyone.

for example; we don’t all have/want the same Xfr Case Low Range ratios.; one reason i did not want a Rubicon with the diesel is i preferred the 2.72:1 ratio instead of the 4:1 of a Rubicon.

a numerically perfect correction for my (current) tire size would have been closer to something around 4.32, but wasn’t an option from any reputable supplier.

I'd avoid using the word perfect. People will get hung up on it. But that's just me.

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[Ratbert]

don’t get so hung up on “perfect”; it isn’t going to be the same for everyone.

for example; we don’t all have/want the same Xfr Case Low Range ratios.; one reason i did not want a Rubicon with the diesel is i preferred the 2.72:1 ratio instead of the 4:1 of a Rubicon.

a numerically perfect correction for my (current) tire size would have been closer to something around 4.32, but wasn’t an option from any reputable supplier.

Is there a reason you prefer that transfer case ratio? I appreciated 4:1 in my JLUR as well as my JLURD. It seems to work exceptionally well, even with dramatically different vehicles / engines / gear ratios.

Hell, I've seen the implications of that 2.72:1 ratio on a Sport attempting to descend Red Cone. They burnt out their brakes, even in 1st / 4lo. That was "exciting".

 

[BuffaloBill]

I’m running 35s (these K02 measure about 34.5) and changed gears to 4.10. Much of what’s good, better, best is personal opinion, depending on use case, etc.

I prefer this gearing to the stock 3.73. A lot of my driving is 55-60mph 2-lane roads. This slight gearing change made a noticeable reduction in the transmission’s dropping to 7th on moderate hills and/or headwind. If I lost any mpg it must be very slight. I occasionally tow either an off-road camping trailer or a tilt bed aluminum car hauler with a subcompact Kubota, and am very happy with this tire & gearing selection.

 

[zouch]

yeah, 2.72:1 is low enough; i don't find i want/need to be going any slower in 4Lo.
only reason i have for wanting a low-range is for dirt and rock fun. our diesels already supply sufficient torque at that ratio, and 2.72:1 with the torque convertor reduces things enough to keep from heating up the transmission/torque convertor too much.

braking has never been a factor for me in choosing a xfr case ratio.
we all know the JL(U)s brakes aren't the best, but we also know not everyone knows how to use brakes. there are solutions for at least one, and probably both, of those factors.

Is there a reason you prefer that transfer case ratio? I appreciated 4:1 in my JLUR as well as my JLURD. It seems to work exceptionally well, even with dramatically different vehicles / engines / gear ratios.

Hell, I've seen the implications of that 2.72:1 ratio on a Sport attempting to descend Red Cone. They burnt out their brakes, even in 1st / 4lo. That was "exciting".

 

[Mr. Curti]

I have the 2020 JLYRD Wrangler with 37 inch tires. I am using the stock 3.74 gears and am having zero issues. I get over 22 mpg and the jeep only drops into 6th gear on steep freeway grades. I honestly don't see the need to regear.

When I was on 35, I think the best I saw was 18 miles to the gallon. Now that I’m on 42s, the best I see is probably 14.5. God bless all of you that get good gas mileage. My ego diesel has always been a pig when it comes to burning diesel.

 

[Compression-Ignition]

When I was on 35, I think the best I saw was 18 miles to the gallon. Now that I’m on 42s, the best I see is probably 14.5. God bless all of you that get good gas mileage. My ego diesel has always been a pig when it comes to burning diesel.

I'm on 40's now and up here in Montana the highway into town has a speed limit of 80 mph. Getting up to about 85mph really sucks the mileage down, but it can still get about 16.5-19. On 37's going about 65 (touching 70 some) I could still get 25mpg. I never saw 30 even on stock 33's. Maybe 27-28...maybe.

 

[grimmjeeper]

I'm on 40's now and up here in Montana the highway into town has a speed limit of 80 mph. Getting up to about 85mph really sucks the mileage down, but it can still get about 16.5-19. On 37's going about 65 (touching 70 some) I could still get 25mpg. I never saw 30 even on stock 33's. Maybe 27-28...maybe.

I touched 30 in my 2021 on 35s with 3.73 gears. Headed east from Denver on the flat 2 lane highways doing 55-65. Probably with a tail wind. Upper 20s was more the norm. I wouldn't dip below 20 unless I was doing a lot of short trips.

Knock 1-2 MPG off with 37s and same axle gears.

 

[Tpsillos]

I'm on 40's now and up here in Montana the highway into town has a speed limit of 80 mph. Getting up to about 85mph really sucks the mileage down, but it can still get about 16.5-19. On 37's going about 65 (touching 70 some) I could still get 25mpg. I never saw 30 even on stock 33's. Maybe 27-28...maybe.

For comparison, I put gas rubi axles in my sport. I've been running 40's for couple years now. Driving around normally around town/highway mix it averages 21 mpg. On the interstate if I keep under 70 mph it will get 24/25 mpg. 80 mph and up it gets 18 mpg at best.

 

[Rangemaster]

Mine averages 18 mpg on 37’s with 5” lift.

 

[Motoristx]

I'm getting 20mpg on the regular. This is 80% highway driven and I tend to keep it at 70 and under.

2020 JLURD, 120k miles, stock 3.73 gears, 39 inch KM3's at 29-30 psi. It hits 8th gear once its warmed up at about 65 and downshifts on all the overpasses to 7th. I feel like it has enough power for me. (Frame of reference here, I've had a 2013 JKU Rubicon auto on 33's, and still own a 1993 YJ 4.0 with 5sp on 33's. Both grossly underpowered compared to this). Speedo done with a Tazer. I'm in Houston so no inclines except for the overpasses which is damn near every quarter mile. I've taken it all over to the west of Texas, Moab, Lake Tahoe, some trails in western Washington and Oregon. When I start driving over 75, mpg starts to drop to 18.5 which is about the lowest I get. All this mileage really comes from daily driving to and from work, which is a 70 miles round trip for me.
Once, I decided to try to hypermiling when I was running the 38 in Patagonia's at about 35psi. I would drive at 55-60 in the slow lane, and when I came to an overpass I'd slowly let off the gas till about 40-45 and accelerate on all the down hills. I did this for about 1 full tank of fuel to get as good as a measure as I could. This tank ended up being 29.8mpg, which is the best I ever got. I will not do it again because it was a pain in the ass and Houston traffic might get me shot if I try again .

I've always wondered with 4.10s would drive like, but they were not an option in 2020 when I ordered mine. At this point, I'd only regear if I put tons on it and went with 42's. If I kept the same 39's I'd probably go with the 4.10's when building tons.

Sorry if I went into a little rant here. I Used to be an Air Force aircraft mechanic, so I keep some meticulous records.

Edit: I did have a bad EGR valve, (its actually the Throttle body valve at the front of the intake). I think it was stuck open or didn't recognize the position. when i was going through that I got the lowest mpg ever, in the 17s everyday driving. This was fairly recently.

 

[Deen]

'21 JLURD with rack and awnings now on 37's. On advice of several places I went to 4.88's, found that was too low when in 4lo as I did most badge trails in 2hi or 4hi. Switched axles to Dana Ultimate 43 front and 60 rear with 4.10 but the MT Baja Boss AT tires are heavy and probably should have gone 4.56 since I weigh over 7K partly loaded.

 

[Deen]

Oops meant Ultimate Dana 44, not 43.

 

[Ratbert]

'21 JLURD with rack and awnings now on 37's. On advice of several places I went to 4.88's, found that was too low when in 4lo as I did most badge trails in 2hi or 4hi. Switched axles to Dana Ultimate 43 front and 60 rear with 4.10 but the MT Baja Boss AT tires are heavy and probably should have gone 4.56 since I weigh over 7K partly loaded.

It sucks that you went to 4.88s and they were too low. That must have been an expensive mistake.

It's a bit bizarre that you were doing badge trails in 2h, but then again, there are supposedly level 1 BOH trails out there. Note that 4.56s are working extremely well for me in my relatively-bloated JLURD.

 

[Deen]

The diesel just doesn't need tor run at higher rpm.

 

[Ratbert]

The diesel just doesn't need tor run at higher rpm.

That has nothing to do with running badge trails in 2h, right?

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