FAD Missing

[Zachanadandy]

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.

Is it an optical illusion or do you have about the exact amount of exposed threads as the portion you cut off? Could you not have just tightened the joint all the way to the jamb nut and not cut anything? All aftermarket arms aren't the same. Many will in fact go all the way down to stock length, and from your photos it looks like even yours would have. Low profile jamb nuts are also available (about half the thickness of the standard ones). Many of the geo brackets have multiple upper holes for dialing in caster, when paired with adjustable uppers you can play with the lengths and mounting positions to get the axle just where you want it. I agree if your lowers were way too long you might have to cut them, but I've yet to run into that on the lift and arm combos we've run.

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[Rusty PW]

Is it an optical illusion or do you have about the exact amount of exposed threads as the portion you cut off? Could you not have just tightened the joint all the way to the jamb nut and not cut anything? All aftermarket arms aren't the same. Many will in fact go all the way down to stock length, and from your photos it looks like even yours would have. Low profile jamb nuts are also available (about half the thickness of the standard ones). Many of the geo brackets have multiple upper holes for dialing in caster, when paired with adjustable uppers you can play with the lengths and mounting positions to get the axle just where you want it. I agree if your lowers were way too long you might have to cut them, but I've yet to run into that on the lift and arm combos we've run.

Screwed all the way in before cutting was a 1/4" too long. After cutting, it screwed down to stock length.

 

[ShadowsPapa]

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.

Not how it works at all. It depends on engine torque output, road speed vs. throttle position and more. The clutches are applied by the computer based on many factors, and it's got to be running and in those conditions before it's locked. The shafts will not be locked while you are under it trying to turn things - engine must be running to lock the clutches in any t-case shifter position.

I have JSCAN screen shots showing how it works.

 

[JeepOfTheseus]

Not how it works at all. It depends on engine torque output, road speed vs. throttle position and more. The clutches are applied by the computer based on many factors, and it's got to be running and in those conditions before it's locked. The shafts will not be locked while you are under it trying to turn things.

I have JSCAN screen shots showing how it works.

Even in 4H Part-time or 4L? I know 4H Auto is a clutch-based engagement, which allows for slippage, but I thought the others were mechanically locked once it's engaged. When I removed the driveshafts originally, I could have sworn I got the front to lock using 4WD.

In any case, I checked the cable and don't see anything wrong (other than some light grease that sprayed in the area, but nothing major). Not sure what my next steps should be. First order of business is to go for a quick drive in 2WD without the front driveshaft to see if that's the source of my vibration. After that, I need to figure out how to troubleshoot the transfer-case further...

 

[ShadowsPapa]

Even in 4H Part-time or 4L? I know 4H Auto is a clutch-based engagement, which allows for slippage, but I thought the others were mechanically locked once it's engaged. When I removed the driveshafts originally, I could have sworn I got the front to lock using 4WD.

In any case, I checked the cable and don't see anything wrong (other than some light grease that sprayed in the area, but nothing major). Not sure what my next steps should be. First order of business is to go for a quick drive in 2WD without the front driveshaft to see if that's the source of my vibration. After that, I need to figure out how to troubleshoot the transfer-case further...

Even 4 low is clutch-based. Yes, it's locked with no throttle use, but it's still clutches and engine must be running.

4 high PART TIME is also clutch - and it's also applied without road speed or throttle use, so it will not slip on turns and so on like 4 high auto will.

In 4 high auto, it applies clutches at the stop and relaxes them as road speed increases but it applies them again as throttle pressure builds.

 

[JeepOfTheseus]

Interesting...I'll have to do more testing. I guess no justification for an Atlas TC...for now...

 

[JeepOfTheseus]

Just to keep adding data: it looks like most, if not all, of my vibration is coming from the front driveshaft. Having removed it temporarily, I was able to go up to 75 mph without any significant vibration. At the very least, with my current caster angle, I was noticing it kick in pretty hard around 70 mph which was much earlier than previous. At this point, I'm going to reinstall the OEM (i.e. Rzeppa joint) and drive around with that for a bit.

Last resort is going back to a two-piece in the rear, which for me likely requires getting some reinforcement plate welded to the carrier crossmember to attach the bracket to.

 

[JeepOfTheseus]

Update: I ended up finding all my FAD components and the stock axles still looked good, so...for better or worse, I reinstalled all of those. The FAD should almost certainly resolve the vibration issues, whether I swap the driveshaft back to stock or not. I'm leaning towards leaving the 1350 in (with the double cardan) because the FAD will prevent it from spinning anyways.

 

[JTGuy]

My '22 came with a FAD. If it did't I would some how have hubs by now. With 4.88s and 2 inch lift and about 8 deg caster I would have front DS vibes for sure.

 

[CrazyCooter]

I have bid out 2 packages including lifts, tires, wheels, and gear jobs in the past month on 2026 JT and JL. I advised the clients that they "may" have a vibration from the front with a 2.5" lift and "will most likely" have a vibration with a 3.5"+ lift.

I'm thinking that swapping in and wiring up the FAD is going to be a requirement to put out the builds that I want to be involved in. Crazy how Ram and Jeep have flipped back and forth on this for years.......

 

[JTGuy]

I did the hub conversion from Yukon on my 14JK. Not cheap and required new wheels. But worth every penny. Now I would just do a D60.

 

[Stan H]

I would love to be able to afford a lock in lock out hub conversion kit.

 

[Rusty PW]

I did the Dynatrac free hub kit on my Power Wagon with the RCV axles at the same time. RCV had axle ends that matched up with the Dynatrac kit. Loved that set up. Wish they would do it for the JL/JT's.

 

[WILDHOBO]

I have bid out 2 packages including lifts, tires, wheels, and gear jobs in the past month on 2026 JT and JL. I advised the clients that they "may" have a vibration from the front with a 2.5" lift and "will most likely" have a vibration with a 3.5"+ lift.

I'm thinking that swapping in and wiring up the FAD is going to be a requirement to put out the builds that I want to be involved in. Crazy how Ram and Jeep have flipped back and forth on this for years.......

It’s so annoying. Either locking hub axles or fads. Otherwise it’s a mess.

 

[WILDHOBO]

I did the Dynatrac free hub kit on my Power Wagon with the RCV axles at the same time. RCV had axle ends that matched up with the Dynatrac kit. Loved that set up. Wish they would do it for the JL/JT's.

ME TOO

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