Interesting Quirk of the FAD.

DavidArmen

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Has anyone else noticed that if you grab the transfer case lever and switch to 4hi then back to 2hi then again to 4hi and repeat this once or twice in succession (2hi->4hi->2hi->4hi->2hi->4hi), when you then finally switch back to 2hi, the FAD does not immediately disconnect.
Normally it disconnects almost immediately after switching into 2hi.
When this is done while driving down the road, it is then extremely easy to pull the lever into 4hi since, I assume, the front driveshaft is now rotating because the FAD hasn’t yet disconnected.
It does eventually disconnect if you don’t go back into 4hi within a few seconds after the quick switching process.
I would guess that it stays connected for about 10 seconds but I’ve only experienced this phenomenon twice so I can’t be sure.
Could it be by design? For example: The jeep thinks you’re switching between 2hi and 4hi fast enough for it to not even bother disconnecting the FAD since it knows you will switch back to 4hi again very soon.
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Headbarcode

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It's only a small electric motor that it actuating a plastic collar. If there's any load, from either acceleration or deceleration, the motor doesn't have the power to bull the collar to the disengaged position.
 

limeade

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It's only a small electric motor that it actuating a plastic collar. If there's any load, from either acceleration or deceleration, the motor doesn't have the power to bull the collar to the disengaged position.
It's actually a metal collar which is actuated to lock the two passenger side axle shafts together. There is a plastic piece in the mix though, might be what you were thinking of. The plastic piece is a bushing which is inside the outer end of the inner axle. A nub, which protrudes from the inner end of the outer shaft (not the stub shaft) rides in that plastic bushing. Not sure why Jeep or Dana decided to use a plastic part there, where something like brass would've done better in that environment.

When I installed my Dana chromoly front shafts, that plastic bushing broke apart very easily when I tried prying it out. It appeared to be pretty fragile after going through some heat cycles.

Here's some pics of what it looks like:

Pic of FAD collar:
thumbnail_IMG_0267.jpg


Plastic bushing in outer end of inner shaft:
thumbnail_IMG_0271.jpg


Pic of "nub" on end of outer shaft which goes into the plastic bushing (stock shaft is on the left, Dana chromoly on right. For the chromoly shaft, the "nub" is larger in diameter and therefore the plastic bushing is not needed and removed)

thumbnail_IMG_0262.jpg
 

Headbarcode

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It's actually a metal collar which is actuated to lock the two passenger side axle shafts together. There is a plastic piece in the mix though, might be what you were thinking of. The plastic piece is a bushing which is inside the outer end of the inner axle. A nub, which protrudes from the inner end of the outer shaft (not the stub shaft) rides in that plastic bushing. Not sure why Jeep or Dana decided to use a plastic part there, where something like brass would've done better in that environment.

When I installed my Dana chromoly front shafts, that plastic bushing broke apart very easily when I tried prying it out. It appeared to be pretty fragile after going through some heat cycles.

Here's some pics of what it looks like:

Pic of FAD collar:
thumbnail_IMG_0267.jpg


Plastic bushing in outer end of inner shaft:
thumbnail_IMG_0271.jpg


Pic of "nub" on end of outer shaft which goes into the plastic bushing (stock shaft is on the left, Dana chromoly on right. For the chromoly shaft, the "nub" is larger in diameter and therefore the plastic bushing is not needed and removed)

thumbnail_IMG_0262.jpg
Oh, that's what is plastic. OK, I just regained a pinch of faith in Dana's design. I'm sitting on a set of rcv axles, which includes a bronze replacement for the factory plastic. Thanks for clarifying! I've been curious to get in there, but am waiting on knuckles to before pulling it apart.
 

Zandcwhite

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Has anyone else noticed that if you grab the transfer case lever and switch to 4hi then back to 2hi then again to 4hi and repeat this once or twice in succession (2hi->4hi->2hi->4hi->2hi->4hi), when you then finally switch back to 2hi, the FAD does not immediately disconnect.
Normally it disconnects almost immediately after switching into 2hi.
When this is done while driving down the road, it is then extremely easy to pull the lever into 4hi since, I assume, the front driveshaft is now rotating because the FAD hasn’t yet disconnected.
It does eventually disconnect if you don’t go back into 4hi within a few seconds after the quick switching process.
I would guess that it stays connected for about 10 seconds but I’ve only experienced this phenomenon twice so I can’t be sure.
Could it be by design? For example: The jeep thinks you’re switching between 2hi and 4hi fast enough for it to not even bother disconnecting the FAD since it knows you will switch back to 4hi again very soon.
I've never had a seizure while shifting between 2wd and 4hi, so no I've never noticed a phenomena created by shifting back and forth a bunch of times? Why would anyone be shifting in and out of 4wd repeatedly and rapidly is the better question?
 

calemasters

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Has anyone else noticed that if you grab the transfer case lever and switch to 4hi then back to 2hi then again to 4hi and repeat this once or twice in succession (2hi->4hi->2hi->4hi->2hi->4hi), when you then finally switch back to 2hi, the FAD does not immediately disconnect.
Normally it disconnects almost immediately after switching into 2hi.
When this is done while driving down the road, it is then extremely easy to pull the lever into 4hi since, I assume, the front driveshaft is now rotating because the FAD hasn’t yet disconnected.
It does eventually disconnect if you don’t go back into 4hi within a few seconds after the quick switching process.
I would guess that it stays connected for about 10 seconds but I’ve only experienced this phenomenon twice so I can’t be sure.
Could it be by design? For example: The jeep thinks you’re switching between 2hi and 4hi fast enough for it to not even bother disconnecting the FAD since it knows you will switch back to 4hi again very soon.

I have not tried that. But I did notice if I shift 4H->4L->4H->4L->4H->4L at 45 mph, it destroys my transfer case.
 

Yellow Cake Kid

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How would you know the FAD status? Is there a dash indicator?

It seems like you would have to observe the front driveshaft while the front wheels were spinning to interpret the position of the FAD mechanism.
 
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DavidArmen

DavidArmen

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I've never had a seizure while shifting between 2wd and 4hi, so no I've never noticed a phenomena created by shifting back and forth a bunch of times? Why would anyone be shifting in and out of 4wd repeatedly and rapidly is the better question?
haha I knew this question would come up! It was to break in the firm transfer case lever while jeep was stationary and then the second time was while rolling about 10mph to test this phenomenon. I shifted back and forth but not as fast as one might imagine, perhaps a 3-4 second pause between each shift and the FAD still did not disengage instantly once back into 2hi as it does normally so it was interesting.

I have not tried that. But I did notice if I shift 4H->4L->4H->4L->4H->4L at 45 mph, it destroys my transfer case.
Looool that’s a good one:CWL:

How would you know the FAD status? Is there a dash indicator?

It seems like you would have to observe the front driveshaft while the front wheels were spinning to interpret the position of the FAD mechanism.
There is no dash status specifically for the FAD but there are multiple ways to tell from inside the vehicle actually. One way is when you shift from 2hi into 4hi, the 4hi indicator will blink until the FAD connects, and then it will go solid. Another way is you can actually hear the electric motor actuate when you shift into 4hi and disengage when you shift back into 2hi, so long as you are stationary and there isn’t too much external noise. Yet another way to know that the FAD was connected when shifting into 4hi from 2hi is the shift lever will be extremely easy to pull into 4hi compared to in normal cases (since the front driveshaft will be live and it will be rotating at an equal rate to the rear driveshaft, making the shift seamless and completely effortless) and the 4hi indicator on the dash will immediately turn on solid without first blinking.
 

Zandcwhite

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I figured it was a breaking in exercise, but I don’t see it being an intentional delay. The sway bar and lockers don’t usually engage right away either. It’s likely waiting for spline alignment.
 
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