Help me diagnose Bronco: 2H stuck in 4A?

[Gotchaa]

Okay 6G wrenchers need some help on this problem. So Bronco has been having rumbling oscillating sounds at freeway speed, starts around 65, strongest at 82mph

Harmonic sound and vibration under drivers floor panel.

Tire balanced checked
Tires in good shape
Driveline checked

Get up to speed and put it in neutral and vibration dissipates going from 80s down to 65, back in drive issues comes back at speed

No difference from 2H to 4A

Got it up on a rack today and took a video showing the behavior in 2H, front drive shaft is moving and all 4 wheels rotating.

Set to neutral and turned the left front wheel and all wheels were turning? Is this normal expected behavior?

What could be the issue?

Front Differential?

Transfer case?

Here is the video to view, take a look at it and let me know what you think 6G wrenchers:

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[Brian_B]

Okay 6G wrenchers need some help on this problem. So Bronco has been having rumbling oscillating sounds at freeway speed, starts around 65, strongest at 82mph

I have no useful input on your issue, but I have a burning curiosity to know if you hit 88 MPH do you go back in time?

 

[BigBendBW]

Differential is what my first thought is…had something similar with a previous vehicle and that was the culprit.

 

[RagnarKon]

Ooooo super interesting.

It would be the transfer case that is doing that. But I'm wondering if that's actually normal behavior and traction control is just kicking in. This is the sort of stuff you'd sometimes see on AWD vehicles, and the Bronco is kinda-sorta an AWD vehicle if you have the Advance 4x4 transfer case

If you still have it up on the lift turn traction control off, and try it again.

 

[Gotchaa]

Ooooo super interesting.

It would be the transfer case that is doing that. But I'm wondering if that's actually normal behavior and traction control is just kicking in. This is the sort of stuff you'd sometimes see on AWD vehicles, and the Bronco is kinda-sorta an AWD vehicle if you have the Advance 4x4 transfer case

If you still have it up on the lift turn traction control off, and try it again.

Didn’t think about traction control, worth a shot.


I am curious if neutral all 4 wheels are suppose to turn like that though

 

[RedShiftWT81650]

seems like you need your transfer case serviced… I read on a very contentious thread about how 4a works and it seems like there is a vulnerable clutch assembly in the transfer case that may be the culprit in your situation… but I’m just an end user.. ¯\_(ツ)_/¯

 

[RagnarKon]

Didn’t think about traction control, worth a shot.


I am curious if neutral all 4 wheels are suppose to turn like that though

Neutral wouldn't have anything to do with it. Neutral effectively disconnects the engine from the transmission. But the transfer case is downstream from the transmission.

On the Advanced 4x4 transfer case there is a clutch pack that activates on the fly to send power to the front wheels, effectively linking the front wheels with the rear wheels. Normally in 2-High you'd expect that clutch pack to be disengaged, but it's all computer controlled and very possible Ford is activating that clutch pack as part of the traction control.

It's also possible that there is enough residual friction in that clutch pack that it turns all four wheels when the vehicle is unloaded on the lift. But you can test that simply by holding the front wheels and seeing if the rear wheels continue to spin.

Or there could be something up with your transfer case. But either way, it's all related to something inside of the transfer case.

 

[dgorsett]

...and when you figure it out you may have the answer to the flat tow issues with the Advanced 4x4.

 

[Oldhippie]

Can ya hold the front wheels and stop them from turning when ya turn the rear? If so I’ll say normal, if not it is in the transfer case…as mentioned front drive clutch…

 

[Gotchaa]

Do you guys think the transfer xas

Can ya hold the front wheels and stop them from turning when ya turn the rear? If so I’ll say normal, if not it is in the transfer case…as mentioned front drive clutch…

In neutral ?

 

[RagnarKon]

In neutral ?

What @Oldhippie and I are trying to figure out is if the front driveline and the rear driveline are in-fact locked together by that clutch pack in the transfer case.

So you got two choices:

1. Stick it in Drive and hold onto BOTH front wheels. If the transfer case is operating as expected... the rear wheels should turn.
2. Put it in Neutral, hold BOTH the front wheels, and spin BOTH of the rear wheels in the same direction. If the transfer case is operating as expected, this should move the rear drive shaft.

Both achieve the same thing.

EDIT— If you don't have enough people around to hold both of the wheels you can use the lockers. Then you'll only have to worry about holding/spinning one wheel rather than both wheels.

 

[Brian_B]

My guess is just not enough friction and it's just some residual motion in the tcase.

Just chock the front wheels (don't want it rolling away from you) and jack up the rear end by itself and try the same test with wheels on the ground.

If they are locked on the Tcase, you aren't moving anything - the rear wheels won't spin by hand at all.

In Neutral, The rear wheels ~should~ spin in opposite directions if they are both in the air and you just spin the rear wheels by hand (you see the open diff trying to push against something - so they spin opposite each other).

*edit* now that I'm thinking too hard about it - I'm not so sure. I am now thinking one tire would move in the "locked T-case" scenario but not both maybe - it would be operating the same as only one tire jacked up since the front wheels would be pinned and locked in via Tcase. Imma try this tomorrow myself because now I'm curious.

 

[Gotchaa]

What @Oldhippie and I are trying to figure out is if the front driveline and the rear driveline are in-fact locked together by that clutch pack in the transfer case.

So you got two choices:

1. Stick it in Drive and hold onto BOTH front wheels. If the transfer case is operating as expected... the rear wheels should turn.
2. Put it in Neutral, hold BOTH the front wheels, and spin BOTH of the rear wheels in the same direction. If the transfer case is operating as expected, this should move the rear drive shaft.

Both achieve the same thing.

EDIT— If you don't have enough people around to hold both of the wheels you can use the lockers. Then you'll only have to worry about holding/spinning one wheel rather than both wheels.

Assuming this is to be done on 2H with traction control off

 

[Brian_B]

Stick it in Drive and hold onto BOTH front wheels. If the transfer case is operating as expected... the rear wheels should turn.

Not sure I'd do this. If the front wheels are being driven and you decide to arm wrestle your engine, I think the engine may win, even at idle. I guess some level of common sense applies and you just don't bear hug the tire...

 

[Gotchaa]

My guess is just not enough friction and it's just some residual motion in the tcase.

Just chock the front wheels (don't want it rolling away from you) and jack up the rear end by itself and try the same test with wheels on the ground.

If they are locked on the Tcase, you aren't moving anything - the rear wheels won't spin by hand at all.

In Neutral, The rear wheels ~should~ spin in opposite directions if they are both in the air and you just spin the rear wheels by hand (you see the open diff trying to push against something - so they spin opposite each other).

*edit* now that I'm thinking too hard about it - I'm not so sure. I am now thinking one tire would move in the "locked T-case" scenario but not both maybe - it would be operating the same as only one tire jacked up since the front wheels would be pinned and locked in via Tcase. Imma try this tomorrow myself because now I'm curious.

Yeah it’s hard to know exactly expected behavior without comparing it to a known working Bronco.

One thing is for sure we tested both lockers and they work fine.

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