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Front Differential?

lonediver2002

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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?
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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?
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).
 

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

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Theoretically you could run different gear ratios in the front and rear diff, but you'd need a tire set-up like this.

Ford Bronco Front Differential? 1616426280587


And the locking differential has no-effect on fuel economy on the highway, because you should never be locking the diff on pavement.
 
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lonediver2002

lonediver2002

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You know you can’t drive on the highway with the rear locked, right?
I was told that with that rear dif, running at highway speed of course not engaged would be pushing the limit at 70-75. It is great for rock crawling.
 

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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).
Not really an understood thing. I kinda looked at it like it was the law. As in if you had say 4.70 gears in rear and 4.10's in front, soon as you go to 4WD things would pretty much explode... So more of a don't do it sort of thing as opposed to yeah it's understood that you shouldn't try it. Know what I'm saying? 😉
 

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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?
 
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lonediver2002

lonediver2002

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Not really an understood thing. I kinda looked at it like it was the law. As in if you had say 4.70 gears in rear and 4.10's in front, soon as you go to 4WD things would pretty much explode... So more of a don't do it sort of thing as opposed to yeah it's understood that you shouldn't try it. Know what I'm saying? 😉
all of that depends on when you engage the 4w dr. I know you do not drive on pavement in 4x.
 

ZackDanger

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Not really an understood thing. I kinda looked at it like it was the law. As in if you had say 4.70 gears in rear and 4.10's in front, soon as you go to 4WD things would pretty much explode... So more of a don't do it sort of thing as opposed to yeah it's understood that you shouldn't try it. Know what I'm saying? 😉
Yeah. I guess I just meant that whenever I've been talking about my Wrangler with people and someone says they changed their "rear end" gearing... there's never a followup question to whether they changed their front gearing as well.

...so for people used to 4wd vehicles on the forum, we're operating under the assumption both are changed together.
 

lobbs611

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I was told that with that rear dif, running at highway speed of course not engaged would be pushing the limit at 70-75. It is great for rock crawling.
Back in 19-dickety-2 that would be sound advice but we've had overdrive transmissions in pretty much everything since the '80s. You're not going to be at redline at 70-75mph unless you're stuck in 2nd, maybe 3rd gear, for some reason.
 

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all of that depends on when you engage the 4w dr. I know you do not drive on pavement in 4x.
If you engage the 4wd at any point with different gearing between front and rear axle you have a problem!

Unless of course like @L8apex posted above, if you do a little math and figure out what size tire to run in the front, you may get lucky 🤷‍♂️
 

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I was told that with that rear dif, running at highway speed of course not engaged would be pushing the limit at 70-75. It is great for rock crawling.
This vehicle is designed to be driven around as a daily driver. The gear ratio is designed to match the tire diameter for typical driving.

The vehicle is (literally) geared for slow speed driving rather than high speed sports car stuff... but I'll be driving at 80mph on the highway all the time with the Bronco without issue.
 

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I was told that with that rear dif, running at highway speed of course not engaged would be pushing the limit at 70-75. It is great for rock crawling.
You'll be able to go faster than 75, that's for sure not a limit. I don't have the post on hand, but somebody did the math and 75mph with a 4.27 would be around 2100-2200 RPM.
 
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lonediver2002

lonediver2002

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This vehicle is designed to be driven around as a daily driver. The gear ratio is designed to match the tire diameter for typical driving.

The vehicle is (literally) geared for slow speed driving rather than high speed sports car stuff... but I'll be driving at 80mph on the highway all the time with the Bronco without issue.
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?
 

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If equipped, both axles will definitely unlock above a certain speed (indicated). The rear in my F150 is 25MPH and from what I have seen the Bronco is the same. The front likely has additional safeguards, as the front locker creates a host of bad outcomes driven at speed while turning. The unlocked axle has no influence over the vehicle at highway speeds.
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