FAD Missing

[WILDHOBO]

Not sure how the geo brackets would lead to a "weird axle position"? They effectively return the axle to its stock geometry and movement after lifting. I don't daily the JT and never have, but the difference the brackets make over washboards is far too good for me to give them up. With 4.5" front springs and 37s it handles bumps better than it did stock on and off road (the triangulated 4 link in the rear is another big part of that). The only negative of the brackets is the little bit of ground clearance lost. I've scraped them on rocks a few times but they've never hung me up. Even on the wife's JLUR that is our rock rig we've never had an issue with the brackets. Not in the rubicon or John Bull or Pritchett canyon.

Because they don’t have oem control arms. And they can only get so short.

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[Rusty PW]

Adjustable uppers could fix the caster while retaining the brackets and Adjustable lowers.

If you adjust the lower arms all the way in, and are still longer than stock. Then add adjustable upper control arms to help with caster. It pushes the axle too far forward with the geo brackets. To fix the issue, you have to cut the lower arms to shorten them up to get back to stock length.

 

[JeepOfTheseus]

Not to completely derail, but this all motivated me to swap in the OEM front driveshaft to see if that resolves the vibration…and now I have a new round of confusion:

I put it into 4H (and 4L), dash light confirms engagement, drove it forward and backward a couple feet, and parked/turned off the engine. When I lift the front wheels, I can spin the front driveshaft freely…

If it’s in 4WD, and the rear wheels are on the ground…how am I spinning the front? I do see the rear driveshaft wiggle (backlash), but the front has no resistance.

 

[Stan H]

Not to completely derail, but this all motivated me to swap in the OEM front driveshaft to see if that resolves the vibration…and now I have a new round of confusion:

I put it into 4H (and 4L), dash light confirms engagement, drove it forward and backward a couple feet, and parked/turned off the engine. When I lift the front wheels, I can spin the front driveshaft freely…

If it’s in 4WD, and the rear wheels are on the ground…how am I spinning the front? I do see the rear driveshaft wiggle (backlash), but the front has no resistance.

The ring gear and short inner shaft on driver side is spinning.

 

[Rusty PW]

Not to completely derail, but this all motivated me to swap in the OEM front driveshaft to see if that resolves the vibration…and now I have a new round of confusion:

I put it into 4H (and 4L), dash light confirms engagement, drove it forward and backward a couple feet, and parked/turned off the engine. When I lift the front wheels, I can spin the front driveshaft freely…

If it’s in 4WD, and the rear wheels are on the ground…how am I spinning the front? I do see the rear driveshaft wiggle (backlash), but the front has no resistance.

If you had a Rubi with the lockers engaged. It wouldn't happened. Everything is locked. You have a open diff in the front.

 

[JeepOfTheseus]

I have an e-locker up front, but regardless…with the rear wheels on the ground and the front raised, isn’t the front driveshaft engaged with the rear in 4H/L? It’s not that I can only spin the wheels/axle…I can rotate the front driveshaft itself by hand. The transfer case flange is rotating 360*.

 

[Stan H]

I have an e-locker up front, but regardless…with the rear wheels on the ground and the front raised, isn’t the front driveshaft engaged with the rear in 4H/L? It’s not that I can only spin the wheels/axle…I can rotate the front driveshaft itself by hand. The transfer case flange is rotating 360*.

Go forward more you may not be fully engaged.

 

[ShadowsPapa]

How would a FAD force spider gears to spin faster?

Ken has it right.

- the left wheel continues to drive the axle. With the carrier not spinning, the motion goes through the spiders and the right axle stub coming out of the carrier. It's why AMC suggested running in 4 wheel drive now and then - to lube the gears.
Those side gears spin the spiders inside the carrier. The right stub spins backwards.

And my 1982 Eagle with FAD and vacuum motors to operate the FAD and t-case still works PERFECTLY after 195,000 miles and 40-some years. It worked very well

 

[ShadowsPapa]

The ring gear and short inner shaft on driver side is spinning.

Ring gear is not spinning. The carrier is stationary. Only the side gears and spiders inside the carrier spin - with the axles.
The point of the FAD was to prevent the heavy carrier and ring gear from spinning and spinning the front drive shaft with it.

 

[JeepOfTheseus]

Go forward more you may not be fully engaged.

Drove forward ~10 feet and still nothing.

 

[Stan H]

Drove forward ~10 feet and still nothing.

 

[Stan H]

I have an e-locker up front, but regardless…with the rear wheels on the ground and the front raised, isn’t the front driveshaft engaged with the rear in 4H/L? It’s not that I can only spin the wheels/axle…I can rotate the front driveshaft itself by hand. The transfer case flange is rotating 360*.

What kind of Transfer case do you have ?

 

[JeepOfTheseus]

What kind of Transfer case do you have ?

OEM Overland (non-Rubicon) with 4H Auto selector, i.e. Selec-Trac. Should be MP3022.

 

[GerryAZ]

What position is transfer case shifter in? What you are seeing is normal in “4 Auto”. It would take more slippage between front and rear to get the automatic mode to engage the clutches. Shift transfer case to one of the locked positions and then front driveshaft should be solidly locked to rear shaft.

 

[JeepOfTheseus]

What position is transfer case shifter in? What you are seeing is normal in “4 Auto”. It would take more slippage between front and rear to get the automatic mode to engage the clutches. Shift transfer case to one of the locked positions and then front driveshaft should be solidly locked to rear shaft.

Tried 4H Part Time and 4L. Pretty sure something is wrong. Weird thing is shifting into 4L is noisy and clunky (like it always is), so I don’t think it’s the cable.

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