Front Differential?

[ZackDanger]

So pretty new to the off road, so is getting the 4.27 Locking Rear Axle Final Drive Ratio a good thing or should I go lower gear?

You should get the gearing ratio that matches the tires you are getting. Anything in the neighborhood of 33-35" tires should probably be 4.xx ratio (for normal driving and stuff).

That said, Ford has already decided what gearing you'll get. There's no stand-alone gearing option... it's all tied with other packages (transmissions, Sasquatch, etc).

So it's not a problem you have to worry about. Ford has already done the math for you.

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[lonediver2002]

You should get the gearing ratio that matches the tires you are getting. Anything in the neighborhood of 33-35" tires should probably be 4.xx ratio (for normal driving and stuff).

That said, Ford has already decided what gearing you'll get. There's no stand-alone gearing option... it's all tied with other packages (transmissions, Sasquatch, etc).

So it's not a problem you have to worry about. Ford has already done the math for you.

So I should not change what differential that comes with the BB, either in 7speed or Automatic?

 

[Laminar]

I see alot about the different rear differentials but nothing about what do they have for the front differential. Can someone please explain this. Also with the 4.27 locking rear Axle what kind of highway speed and mileage will it get?

The 4.27 is only available on the automatic BB or OBX so I'll assume the auto trans an a 32" tire. In top gear at 70mph you'll be just under 2000rpm. If wind resistance wasn't a thing, you could top 210mph in 10th gear. Gearing is just fine, the Bronco's ability to cruise at speed will far outweigh the stock tires' ability to live at high speeds. Go as fast as you want - the tires will explode before you reach the limit of what the thing can comfortably cruise at.

Are the locking diffs limited by speed similar to the sway bar disconnect? Sway bar automatically re-connects at 25mph+...will the diffs "un-lock" at a certain speed or is it all driver input?

The regular F-150 automatically unlocks the rear once you're over 25mph. The Raptor allows the rear locker to be used at higher speeds as long as you're in the "off-road" drive mode. The Bronco could use either system, we don't know yet.

 

[Paul Gagnon]

Maybe I'm the only one here but I took the question as to what make and model of front differentials were available, not gear ratios.

 

[ZackDanger]

So I should not change what differential that comes with the BB, either in 7speed or Automatic?

Are you interested in changing the tires on the BB? How do you intend to use your BB and/or what role do you plan it to fill in your life?

 

[lonediver2002]

Are you interested in changing the tires on the BB? How do you intend to use your BB and/or what role do you plan it to fill in your life?

well I am planning on trips to south-west Texas and mountains of south east.

 

[Natai]

Are the locking diffs limited by speed similar to the sway bar disconnect? Sway bar automatically re-connects at 25mph+...will the diffs "un-lock" at a certain speed or is it all driver input?

It depends on the GOAT mode actually.

In the on pavement modes (Normal, Sport, Eco, Slippery), the rear locker is only available under 25mph. In the off-road modes (Sand, Mud/Ruts, Baja, Rock Crawl), the rear locker is available at any speed.

The front locker is only available in 4L and under 25mph, and it's not available in Sport or Eco.

 

[EvlNvrDys]

well I am planning on trips to south-west Texas and mountains of south east.

I think @ZackDanger is trying to ask:

Do you need the rear locker?

BB manual trans has the 4.46 gearing standard (if I'm correct)
BB auto comes with 3.73's? without the locker.
BB w/locker upgrades to 4.27's (if I got my numbers correct)

So it comes down to, will you need the locker? Most people don't. Some of the things I considered when looking at the BB was:
1. I was going to run 285's (33's) and
2. I planned on towing up to the 3500lb max. Therefor I was considering adding the locker to get the new gears.

In the end though, I chose to add the Squatch package.. Problem solved.

In the end, the standard DD can get away with the 3.73 gears.

 

[ZackDanger]

well I am planning on trips to south-west Texas and mountains of south east.

I think the simplest answer is that the standard ratio will be fine for your use case.

If you're not already someone who knows they want something different, it's unlikely that you are going to need or want the optional diff gearing...

...so then the question comes down to whether you want the locking rear differential.

That's probably a question better answered by someone who uses them... but I will say that my jeep doesn't have lockers and I've never missed them for simple overloading and logging trail stuff.

 

[AcesandEights]

I see alot about the different rear differentials but nothing about what do they have for the front differential. Can someone please explain this. Also with the 4.27 locking rear Axle what kind of highway speed and mileage will it get?

The front and rear differentials are "Dana" differentials. Depending on the trim, you have different Dana differentials. The difference is really the size of the gears, the internals. There are larger ring and pinion (gears), and that determines strength. Front and rear differential gearing needs to match (or be very close). If they are not the same, the drivetrain will bind, or the tires will wear more and screech, or they will lose traction off road. Ultimately the tires will turn at different speeds. This will break or wear things out on road.

The differentials are sized (the gearing, for example 4.7:1) to accommodate tires size and how the vehicle will be used off road. Ford has determined the sizes, and either will work fine. The differential gearing will impact RPM, but the transmission is obviously part of the equation and the gearing in the transmission includes overdrive (less than 1:1 gearing) which brings the RPM down to be more fuel efficient. No one knows yet what kind of mileage you will get, as Ford hasn't published EPA ratings yet. You'll be able to drive faster than any posted speed limit in the US.

You have choices in differential gearing which will impact the highway RPM, but more importantly will effect the "crawl ratio" (torque multiplication) off road. That's kind of the point of having those gearing choices, to provide for more off road torque and accommodate for larger tires. The locker doesn't have an impact on your highway speed or mileage. You can use a locker (not necessarily the Ford locker, by design) at any speed, but it impacts the handling. Ford likely has the locker(s), front and/or rear, disconnect at highway speed. This will save wear and tear on the drivetrain and tires and keep it from handling funny at higher speeds. Auto manufacturers will tend to have the locker disconnect at speed so you don't get those quirky handling issues on road.

ETA: as an aside, maybe helpful to the understanding of differential strength, the "number" used is/was the ring gear size in inches or millimeters. So you'd see either in inches, "Ford 10.5" meant a 10.5" ring gear, or something like a Dana 210, which is in millimeters and equates to a 8.27" ring gear. Often you'll hear someone say, a Chrysler 8.25", Ford 9", Toyota 8", etc. and that's kind of an indicator of strength. There are other differences in design, axle diameter, how they are retained, etc. that gets all in the weeds, but you can sort of equate ring gear, and subsequently pinion gear, to axle strength. A Dana 44 is basically the size of a Chrysler 8.25 slightly larger than the Toyota 8" (although the spline count, semi/full-float, c-clip, etc all plays into what is the weakest link in the differential).

 

[lonediver2002]

The front and rear differentials are "Dana" differentials. Depending on the trim, you have different Dana differentials. The difference is really the size of the gears, the internals. There are larger ring and pinion (gears), and that determines strength. Front and rear differential gearing needs to match (or be very close). If they are not the same, the drivetrain will bind, or the tires will wear more and screech, or they will lose traction off road. Ultimately the tires will turn at different speeds. This will break or wear things out on road.

The differentials are sized (the gearing, for example 4.7:1) to accommodate tires size and how the vehicle will be used off road. Ford has determined the sizes, and either will work fine. The differential gearing will impact RPM, but the transmission is obviously part of the equation and the gearing in the transmission includes overdrive (less than 1:1 gearing) which brings the RPM down to be more fuel efficient. No one knows yet what kind of mileage you will get, as Ford hasn't published EPA ratings yet. You'll be able to drive faster than any posted speed limit in the US.

You have choices in differential gearing which will impact the highway RPM, but more importantly will effect the "crawl ratio" (torque multiplication) off road. That's kind of the point of having those gearing choices, to provide for more off road torque and accommodate for larger tires. The locker doesn't have an impact on your highway speed or mileage. You can use a locker (not necessarily the Ford locker, by design) at any speed, but it impacts the handling. Ford likely has the locker(s), front and/or rear, disconnect at highway speed. This will save wear and tear on the drivetrain and tires and keep it from handling funny at higher speeds. Auto manufacturers will tend to have the locker disconnect at speed so you don't get those quirky handling issues on road.

Thanks, that is great info. So going with the 4.27 Locking Rear Axle Final Drive Ratio , 10 speed Auto and standard rear locker is good?

 

[AcesandEights]

Yes, that's good. If I was getting the auto trans, that's what I'd get.

 

[Neps]

You know you can’t drive on the highway with the rear locked, right?

Someone needs to tell my Scout II with a full locker in the rear that, I've been driving on the street for years with it.
Not to mention all the guys driving with a spool or Lincoln Locker

 

[TeocaliMG]

It is understood that both front and rear differential gear ratios must match for things to work correctly... so when someone talks about "rear differential" gearing they really mean both (on a 4wd vehicle).

Fun fact: my pickup has a 3:55 rear and 3:54 front, that's an OEM offering too! but yea generally they are the same, in terms of this thread or the Bronco you are absolutely right. As for my truck, my guess is they were constrained by the different hardware/package space available since the front end isn't as heavy duty as the rear. Also I figured it might actually function better since a slightly taller front ratio will make up for natural front end wander as you steer anything but a perfectly straight track (impossible on an old pickup).

 

[buzpro]

The differentials are sized (the gearing, for example 4.7:1) to accommodate tires size and how the vehicle will be used off road. Ford has determined the sizes, and either will work fine. The differential gearing will impact RPM, but the transmission is obviously part of the equation and the gearing in the transmission includes overdrive (less than 1:1 gearing) which brings the RPM down to be more fuel efficient. No one knows yet what kind of mileage you will get, as Ford hasn't published EPA ratings yet. You'll be able to drive faster than any posted speed limit in the US.

good info .... so on a daily driver with a 4.27 and the 255/70R18 that come on the OBX, how much of a bigger tire can i go with in std. condition without getting a lift .... without affecting ANYTHING adversely? such as braking and stopping distances?
would 265/75-18's work?

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