Help - Locking Rear Axle Question

@mdepll Quite simply an open differential will only supply power to 1 wheel. Limited slip will apply the 2 wheels as needed however, a locked differential will allow you to “lock” the 2 wheels so they ALWAYS turn at the same rate. Locked differentials for off road vehicles are preferred in order to provide maximum traction.

thank you? so if rear are locked at 4.27 ratio then what's ratio for front wheels? how much of an impact on gas mileage will there be?

mdepll

thank you? so if rear are locked at 4.27 ratio then what's ratio for front wheels? how much of an impact on gas mileage will there be?

The front axle and the rear axle will have the same 4.27 ratio. There is a little different RPM difference between the two but shouldn't be a big deal. I suppose if you were DD on-road only and putting a lot of miles on it, then the 3.73s are the way to go.
Look at this thread and you can see the RPM difference. Looks like there is about 250rpm difference at 70mph.

https://community.thebronconation.com/forums/threads/broncos-rpms-70mph-for-each-series.2377/

mdepll

thank you? so if rear are locked at 4.27 ratio then what's ratio for front wheels? how much of an impact on gas mileage will there be?

Please understand that rear differential is only locked when you select the appropriate GOAT mode that will cause it to be locked. It will be a traditional open differential until you select it to be locked. Gear ratios are totally different than locked differential - the gears are in the differential and determine how many times they spin for each revolution of the axle (wheel).

thanks...just trying to understand the impact on gas mileage to see if it's worth it

Deano Bronc

The front axle and the rear axle will have the same 4.27 ratio. There is a little different RPM difference between the two but shouldn't be a big deal. I suppose if you were DD on-road only and putting a lot of miles on it, then the 3.73s are the way to go.
Look at this thread and you can see the RPM difference. Looks like there is about 250rpm difference at 70mph.

https://community.thebronconation.com/forums/threads/broncos-rpms-70mph-for-each-series.2377/

thanks, I realize the pros of having it, just trying to figure out the cons....gas mileage would be a big one and can't figure out what difference that would be

mdepll

thanks, I realize the pros of having it, just trying to figure out the cons....gas mileage would be a big one and can't figure out what difference that would be

Ford hasn't realized MPG figures for the Bronco, so it's hard to compare.
Are you going to be driving on challenging trails? Snow? Sand?
If so, you need a locker. If not - save your money.

The locker doesn't impact fuel mileage, but the gearing will. You will turn higher rpms at any given speed, but it is minimal (15%). How much the change in RPM makes to fuel efficiency is anyone's guess. It won't be a straight 15% though.

3Dogs

Ford hasn't realized MPG figures for the Bronco, so it's hard to compare.
Are you going to be driving on challenging trails? Snow? Sand?
If so, you need a locker. If not - save your money.

Trails and snow for sure. Sand a little. No rock climbing

AcesandEights

The locker doesn't impact fuel mileage, but the gearing will. You will turn higher rpms at any given speed, but it is minimal (15%). How much the change in RPM makes to fuel efficiency is anyone's guess. It won't be a straight 15% though.

That’s what’s difficult to measure and what I’m looking for to justifying cost. Thx anyway

mdepll

Novice here, so please don't jump all over me. It has been suggested that I should consider adding a locking rear diff on my big bend. Not knowing much, outside of traction advantages and higher fuel cost. Can someone please explain what's the difference between 3.7s open that's included and the 4.27 rear locking that's suggested. Thanks

Two reasons people go with a larger gear like the 4.27 or 4.7. They are either towing a boat or trailer of some sort or they want to run larger off road tires like the sasquatch package. That chart was a good example. While the rpms might be slightly higher, if you are running larger tires or towing you will actually see the same or even increased MPGs with a larger gear. Your final drive ratio and RPMs depend on the gearing and tire size combination. It is a balance getting it right. Also consider what engine you are choosing. Smaller less power engine choice definitely calls for taller gears if you want big tires or want to tow. You will definitely suck more gas when you try to get your rig moving while towing or having large tires if you have to use a heavy foot every time you want to accelerate with smaller gears like the 3.73. Taller gears will save fuel in those scenarios.

It is actually pretty cost effective through Ford to upgrade the gearing. Aftermarket will cost more, especially if you have a reputable shop do the work (and you definitely want someone who specializes in re-gearing do the work). IMO if you know you are gonna tow or run larger tires then do it through Ford when you order.

As far as the locking rear diff goes unless you do some very serious off-roading you will probably never use it. If your snow driving is on snow covered paved and plowed roads you will never use it. It is simply not needed on your average trail or forest service road. Deep mud or the Rubicon trail yes. Using it on pavement is a fast way to rack up thousands in repairs. The locking rear diff by itself will not affect MPGs either.

I won't be towing a boat or trailer.

I will be off-roading 4 seasons on light to moderate trails and no rock climbing

Part of me sees it as a investment too if I ever sell this thing. All provided that adding rear locker (which means 4.27 gear ratio) doesn't change my mileage much

mdepll

I won't be towing a boat or trailer.

I will be off-roading 4 seasons on light to moderate trails and no rock climbing

Part of me sees it as a investment too if I ever sell this thing. All provided that adding rear locker (which means 4.27 gear ratio) doesn't change my mileage much

I guess I'm not sure how you will ever know if it changes your mileage a lot or not. Ford is going to just do one mileage rating, so there won't be a different rating for each set of gears.
It's basically a big brick running down the highway powered by turbo charged engines. Not sure what you are really expecting. I would think low 20's highway, maybe slightly higher.

Deano Bronc

I guess I'm not sure how you will ever know if it changes your mileage a lot or not. Ford is going to just do one mileage rating, so there won't be a different rating for each set of gears.
It's basically a big brick running down the highway powered by turbo charged engines. Not sure what you are really expecting. I would think low 20's highway, maybe slightly higher.

Appreciate your response. I guess what I am asking the more experienced folks on here is based on experience? moving from 3.73 to 4.27 or is there nothing to compare it to?
Sounds silly, but are gas costs going from $1 per week to 1.25 per week because of the 4.27 gears?

mdepll

Appreciate your response. I guess what I am asking the more experienced folks on here is based on experience? moving from 3.73 to 4.27 or is there nothing to compare it to?
Sounds silly, but are gas costs going from $1 per week to 1.25 per week because of the 4.27 gears?

It's all up in the air right now until we actually get our hands on these glorious vehicles . I prefer the 4.7 gearing direct from Ford if it is available . The vehicle will have more pep and accelerate quicker . You're not going to be trying to go 130+ in this thing so better to have the power where it's useable , plus if you're going the 10 spd Auto transmission route it will just go to a higher gear on the hwy than perhaps it would with 3.73's . I don't think MPG will suffer a whole lot and as the above poster stated , in a lot of situations it may increase your MPG .

reassuring and confusing at the same time.

yes, I am going with 2.7 AT

thx to both of you for trying to dumb it down for me. I am leaning toward staying with 4.27 rear locker

Great thread guys very good information

I've had two Toyota Tundras. Both had the exact same setup as far as tire size goes and body style. They both had the gas guzzling 5.7L V8 and same transmission. Only difference was the tow package on the second Tundra. The tow package came with a 4.30 rear end and the 2012 Tundra with no tow package was a 3.92. I couldn't tell any difference in MPGs but you could definitely tell it had better acceleration with the 4.30. Hope that helps.

Thanks