35s, gears, and lockers on a 99

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olija

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I've been doing some research on what direction I want to be heading with my 99 Expedition with 3.73's. So far I've bought a 2" suspension lift and 35x12.5R17 BFG KO2's. From what I am reading, the best aftermarket gearing option for 35" tires is 4.56:1, correct?
I was doing some work on the rig last week and discovered the rear LSD clutches are burned up and several of the teeth where the metal plates engage with the differential case are busted off, apparently a common problem. So I did some looking around and see there aren't a ton of options, basically:
Open, welded, rebuild factory LSD, Yukon Dura-Grip, Detroit TrueTrac, Detroit Locker, ARB Air Locker
Not interested in downgrading to open, ARB is too expensive, Detroit Locker or welded sucks to drive on the street, TrueTrac isn't a true locker, Dura-Grip doesn't sound that much better than factory, and the factory unit broke for a reason so I'm hesitant to just replace it and cross my fingers.

I also saw an old thread from some guy who did a bunch of research to see if a locker from a 09+ F150 FX4 would bolt up into our trucks but there was no conclusion to the thread. Has anyone on here confirmed this?
The thread was suggesting the axleshafts might not be compatible but I don't see why that is. All the lockers that fit the 97-02 F150 and Expedition also seem to fit the 09+ F150s. Is the only difference the number of wheel studs? That wouldn't be too hard to solve with some adapters...

Suggestions welcome!
 

sc99expy

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Following. I’ve got a 99 that I want to use for the beach and trails on weekends. Hopefully someone can help out with the info
 
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olija

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I've done some more thinking about this over the last few days. If I go with 4.10's then I'll be slightly under-geared, and if I go with 4.56's I'll be over-geared by a little bit more. But the area where we live is very hilly, usually we are driving around with 4 kids and 2 adults at a minimum, and loaded down with camping gear it would probably make sense to have a little extra torque. So I'm leaning more towards the 4.56s.
I was looking on Jeff's Bronco Graveyard and found the gears there, also found they sell a LSD rebuild kit for $100 US, which is pretty cheap. But I would really like to find some definitive answers regarding this FX4 e-locker because that is the best of both worlds and the junkyard price might not be too bad.
Here is the link for the e-locker swap, that is lacking follow-up:
 
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olija

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I did a little more research and it's looking like this is probably going to work. Here is another link saying as much:

I've been trying to confirm if the axleshafts are compatible. It looks like they are too. Both are 34 spline. The newer ones are 6-lug and the older ones are 5-lug. According to RockAuto, the wheel bearing part #'s are the same, so I don't see any reason why this won't work.

Also it sounds like the locker is simply activated by 12v in and out, so it should be very easy to wire up.
 
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