Front Diff Grenaded

[Glade Runner]

My front diff on my 21 badlands delivered Jan 22 with 65K on it grenaded going down the highway. Service group said it was probably related to using 4A so much. I drive on snowy roads everyday for 7-8 months a year. Anyone else heard of similar experiences?

Either it’s BS or they are saying their product is inferior.

I had a Jeep Grand Cherokee that had their selectrac full-time 4wd (I.e. AWD). It did have a catastrophic failure at 250K. However that failure was caused by sitting at a stoplight while getting rear ended…

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[flip]

I think the reality is, for those with full plates ( ), you really either need to learn to do it yourself (and pull all the plates), or find a place you trust will do the checks (and pull all the plates for them).

Absolutely and if you service at ANY facility that claims to do a multi-point inspection, remind them to check diff and t-case fluid levels.

 

[RIDE]

…or find a place you trust will do the check (and pull all the plates for them).

Picturing them just standing casually behind you as you make them look completely incompetent…

 

[crenca]

This might be unpopular opinion but my take is there COULD be a link there based on the logic that 4A keeps your front axle engaged the entire time, even at 80MPH at highway posted speeds...

Except 4A does not keep your front axle engaged "the entire time" nor "at 80MPH" - that is not its programming "logic"

If a person wil observe the gauge "Power Distribution" it can be seen what the systems engagement logic actually is. In summary, front axle is engaged only at lower speeds, <30 or 35 mph, and at mild steering input. As speeds build (and as steering input becomes greater) the clutch sends less and less torque forward as well - in other-words allowing differentiation between front and rear axle speeds. Standard AWD stuff.

As for what the OP says his 'service group' says, it is much more likely they are shooting from the hip then anything else (amazing, a dealership shooting from the hip, hard to believe ). Who knows, maybe they know something - an impending TSB maybe...

 

[userdude]

Picturing them just standing casually behind you as you make them look completely incompetent…

Oh, when that guy drained the oil onto the engine plate, I had JUST TOLD HIM to remove the plate and how easy it was... Like literally standing there, when he was underneath. Nod, nod, "Ok, sure", go back inside and .

That was actually beat by that one time the same place used a ladder to take the spare off while it was jacked up off the ground. I seriously thought someone was going to get hurt that time.

 

[crenca]

that one time the same place used a ladder to take the spare off while it was jacked up off the ground. I seriously thought someone was going to get hurt that time.

LOL, sounds like a Steven Wright skit...

 

[Brian_B]

Except 4A does not keep your front axle engaged "the entire time" nor "at 80MPH" - that is not its programming "logic"

Hmm.

Not sure it matters so much about 4A or not.

Yeah, it's possible 4A could result in some binding when you wouldn't like it. But I think that probably is not the issue here - the system is fairly intelligent and a lot of people have a lot of miles on 4A by now that I don't think that's the biggest problem. I don't think this is a transfer case issue at all.

Like Snacktime and BigMeatsBronco say - FDU issues are usually traced back to the fact that the FDU is constantly engaged because there are no hub disconnects (even with a FAD, that only affects one of the axles, not both, for "Fuel savings"), the CVs are transferring a lot of stress to the FDU based on how they install, and all of that usually compounded by heavier-than-stock tires or more aggressive suspension setups.

I know when I last changed my FDU oil, there was more "sand" in it than oil from the gears - with about 30k miles on that fluid. I run 35's on a m190, I have a 2.5" lift, and I have a FAD. Won't be long before some gear in there starts slipping, and then it's gonna be Crunch-Boom time.

If you want your FDU to last forever, keep the front end and tires stock.

 

[RIDE]

Except 4A does not keep your front axle engaged "the entire time" nor "at 80MPH" - that is not its programming "logic"

If a person wil observe the gauge "Power Distribution" it can be seen what the systems engagement logic actually is. In summary, front axel is engaged only at lower speeds, <30 or 35 mph, and at mild steering input. As speeds build (and as steering input becomes greater) the clutch sends less and less torque forward as well - in other-words allowing differentiation between front and rear axle speeds. Standard AWD stuff.

As for what the OP says his 'service group' says, it is much more likely they are shooting from the hip then anything else (amazing, a dealership shooting from the hip, hard to believe ). Who knows, maybe they know something - an impending TSB maybe...

Ya, not saying I have a 100% grasp on how 4A is designed in these, but unless there’s clutches in the front diff or somehow at the individual R&L hubs (or there’s such thing as a high speed actuator solenoid) that front axle and hubs are engaged and spinning while in 4A, right? Maybe it’s disengaged at the xfer but pretty sure the front driveshaft is still spinning at equal rate/speed as rear driveshaft coming out of the xfer, only not under load. Do I have that right?

 

[Ducati1098]

Except 4A does not keep your front axle engaged "the entire time" nor "at 80MPH" - that is not its programming "logic"

If a person will observe the gauge "Power Distribution" it can be seen what the systems engagement logic actually is. In summary, front axle is engaged only at lower speeds, <30 or 35 mph, and at mild steering input. As speeds build (and as steering input becomes greater) the clutch sends less and less torque forward as well - in other-words allowing differentiation between front and rear axle speeds. Standard AWD stuff.

It really has nothing to do with speed. It's throttle input based.
If you're going 80 mph and you start to accelerate, it will send power to the front based on how much you're trying to accelerate.
However if you're just cruising at 80 with little throttle input, it's likely sending very little power (or maybe none at all depending on the situation) to the front.

 

[crenca]

I wish I had paid more attention to the FDU at my 5k oil change. I know I looked at it, but I honestly can't remember exactly what I saw, just the thought "it's fine" . I am planning on a remote wheeling trip tomorrow, now thinking I better get the skid off and do a thorough inspection today...

Maybe drain/inspection/fill on these diffs every 10k is not overkill after all.

unless there’s clutches in the front diff or somehow at the individual R&L hubs (or there’s such thing as a high speed actuator solenoid) that front axle is engaged at hubs and is spinning while in 4A, isn’t it? Maybe it’s disengaged at the xfer but pretty sure the front driveshaft is still spinning at equal rate/speed as rear driveshaft coming out of the xfer, only not under load. Do I have that right?

As I understand it your right, no hub disconnect on trims with 4A so FDU is 'free wheeling' the whole time, but that is a separate issue from whether 4A is sending torque or not to front axle - unless someone wants to explain different

It really has nothing to do with speed. It's throttle input based.
If you're going 80 mph and you start to accelerate, it will send power to the front based on how much you're trying to accelerate.
However if you're just cruising at 80 with little throttle input, it's likely sending very little power (or maybe none at all depending on the situation) to the front.

I will have to test this out. I recall that with almost any throttle input over about 40mph no torque is sent forward (as indicated by the gauge), but perhaps I was not mashing it down enough

 

[Brian_B]

Also, to chime in on the derail -

I don't have 4A in the Bronco, but I had in in a F150, and see the AWD system in the Explorer and Sport.

Pretty sure it's Torque based. Now, wheel speed is a component in calculating torque sent to the wheels, but just one part of that equation. Throttle input is a big one too. And there are probably a dozen other things that go into that equation.

The Bronco can't really do per-wheel torque like the AWD system can, but it can see if the rear is starting to push and send power to the front to assist in pulling.

 

[Brian_B]

As I understand it your right, no hub disconnect on trims with 4A so FDU is 'free wheeling' the whole time, but that is a separate issue from whether 4A is sending torque or not to front axle - unless someone wants to explain different

You are correct - two different issues here. But the OP says they were in 2H when the failure happened, so ...

The only reason we are really talking about the Tcase at all is because the Dealership blamed the failure on 4A.

 

[RIDE]

As I understand it your right, no hub disconnect on trims with 4A so FDU is 'free wheeling' the whole time, but that is a separate issue from whether 4A is sending torque or not to front axle - unless someone wants to explain different

Ya, not saying I’m ready to die on this hill, but this right here is the root of my theory 4A may have something to do with early front diff wear and issues. One example of this might be to pair this with Flips point about not realizing you’re low on fluid and voila, your front diff toasts itself while free spinning on freeway.

edited for clarity

 

[crenca]

FDU issues are usually traced back to the fact that the FDU is constantly engaged because there are no hub disconnects (even with a FAD, that only affects one of the axles, not both, for "Fuel savings")

I just grocked what you said here - is this right, the FAD system on the Bronco only disengages (i.e. the wheel/axle from the FDU) on one side? This would mean that one side (whichever side the FAD is on) is getting a touch less resistance then the other, which effects steering and alignment, at least theoretically...maybe the difference is not enough to matter practically, but then that would beg the quesiton if the FAD itself has any material effect at all - maybe it is all for show for the EPA??

Ya, not saying I’m ready to die on this hill, but this right here is the root of my theory 4A may have something to do with early front diff wear and issues. Pair this with Flips point about not realizing you’re low on fluid and voila, your front diff toasts itself while free spinning on freeway.

Well, I think it comes down to the engineering of the FDU itself. I mean, the whole point of the device is enable torque distribution to the front axle - it's meant to be used. What the OP's dealer is saying is in essence "it's not designed and/or manufactured well enough to be used much at all". In other words 4A (or 4H or 4L) is not itself a reason why the FDU is failing, or should not be. Sort of like if a wing falls off an airplane the manufacture says "your flying too much". In other words there is nothing inherent in 4A that would be different then say 4H - as long as 4A's programing logic is consistent with what is widely known to work and be reliable. AWD systems have had this down for the past 40 years or so, with many different models from many different manufacturers with billions and billions of reliable miles put on them.

It could be that dealers/ford are aware of a specific problem with 4A's logic that is putting a stress on the FDU that it was not designed for, but I sort of doubt it (and it could be fixed with a software update in any case) - it is more likely the FDU is simply not robust enough for the Bronco under normal use case or the FDU's are not being put together well at the factory, probably the latter.

 

[87-Z28]

The issue is the the cv axle stubs shafts are poorly supported. This causes the seals to wear out and put stress on the internal spider gears. Couple this with no front hub disconnects you get substantial wear as seen in the metal found during oil changes.

the CVs are transferring a lot of stress to the FDU based on how they install, and all of that usually compounded by heavier-than-stock tires or more aggressive suspension setups.

lateral loads quickly increase when CV angles increase (lift). OEM SAS CV angles are near zero at oem ride height, hence very little lateral loading. No one wants to hear this but it is simple geometry. Better lateral support is required as CV angles increase.

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