Fad delete and rcv axle.

[Jtphoto]

Mostly correct, however, it appears that because the JL has the FAD they weren’t so critical with pinion angle/caster specs when setting up these diffs since the FAD eliminates the rotation of the diff in 2wd and thus alleviates the vibration caused by improper pinion angle which can not be achieved on this diff without sacrificing optimum caster angle for proper geometry.

This argument no longer stands. As of 2024 the only model JLs left that have a FAD seem to be the Saharas. All the 24 Sports, Willys and Rubicons I’ve seen all have FAD deleted from factory.
The FAD was introduced for fuel economy, nothing more, and certainly not to reduce driveline vibration. The models with 4 auto and the 392 would have consistent problems if that were the case as they are in FAD locked mode in 4Auto or in the case of the 392 Total FAD delete from factory.

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[Fleeclan]

This argument no longer stands. As of 2024 the only model JLs left that have a FAD seem to be the Saharas. All the 24 Sports, Willys and Rubicons I’ve seen all have FAD deleted from factory.
The FAD was introduced for fuel economy, nothing more, and certainly not to reduce driveline vibration. The models with 4 auto and the 392 would have consistent problems if that were the case as they are in FAD locked mode in 4Auto or in the case of the 392 Total FAD delete from factory.

My JLUR is a 2021 so I’m stuck with FAD unless I go to an aftermarket diff. That being said, I have balanced front shaft, all components are in perfect condition and with caster in sweet spot the pinion angle is off just enough to cause vibration when front diff is engaged in 4H at moderate speed so a FAD delete axle setup would introduce vibration. With optimum pinion angle my caster is slightly too negative to drive the way it should. If I had zero lift that would be a different scenario but I don’t so there’s the conundrum.

 

[Jtphoto]

My JLUR is a 2021 so I’m stuck with FAD unless I go to an aftermarket diff. That being said, I have balanced front shaft, all components are in perfect condition and with caster in sweet spot the pinion angle is off just enough to cause vibration when front diff is engaged in 4H at moderate speed so a FAD delete axle setup would introduce vibration. With optimum pinion angle my caster is slightly too negative to drive the way it should. If I had zero lift that would be a different scenario but I don’t so there’s the conundrum.

I have 4Auto option 3.5” lift, factory driveshafts and axles on 37s with factory 4.56 gears. I use MC Geometry correction brackets to get my caster over 5 degrees and have 0 vibe issues at all running down the highway in 4Auto or FAD bypassed.
I am curious as to what is causing your vibes. Do you have a double cardan driveshaft? EDIT: I see now you posted you do have double cardan front shaft. That in itself poses different issues.

 

[Plumbean]

Thought it would be worth mentioning.

Wranglers with the All-Wheel-Drive T-case are paired with a factory axle that does not have a 2pc axle and FAD.

Jeep would likely not offer the AWD t-case if they expected heavy driveline vibrations from the front axle geometry. (my assumption is the geometry between the FAD and non-FAD axles is the same)

This is not correct. Perhaps for the 392s that don’t have 2H? But my 2023 JLUR XR with the AWD t-case has a FAD.

 

[kah.mun.rah]

Mostly correct, however, it appears that because the JL has the FAD they weren’t so critical with pinion angle/caster specs when setting up these diffs since the FAD eliminates the rotation of the diff in 2wd and thus alleviates the vibration caused by improper pinion angle which can not be achieved on this diff without sacrificing optimum caster angle for proper geometry. So if you do a FAD delete you either sacrifice driveability to get right pinion angle and not have a vibration or have a jeep that drives well but vibrates. No true solution other than replacing entire diff or if keeping the OEM D44 with FAD, trussing the diff housing and going to an upgrade in axles that have two piece passenger axle such as the RCV axles for FAD. Two choices in the RCV’s; the standard FAD axle set for $1450 or the 300M FAD axle set (stronger) for $1950.

I have 4” of lift, JKS adjustable track bars, JKS adjustable lower control arms front and rear, JKS adjustable rear sway links, Rock Krawler adjustable front control links as well as a Tom Woods double cardan front drive shaft. All steering components are in perfect shape. I’m on 37’s. My alignment specs are perfect and my Jeep drives great, however without sacrificing my drive quality I can’t get front pinion angle close enough to delete the FAD without vibration.

I’m posting to basically clarify what everyone is saying in response to your post because the way you worded it I think came across wrong. You said if you delete FAD and have vibration then it means you have another problem. Essentially that’s correct but it’s not a problem that is correctable while keeping proper specs and front end geometry because the “problem” is inherent to the OEM JL D44 front diff design.

Yes, with 4" of lift on a OEM JL D44 you will need all of the help you can get avoiding vibration.

 

[Fleeclan]

I have 4Auto option 3.5” lift, factory driveshafts and axles on 37s with factory 4.56 gears. I use MC Geometry correction brackets to get my caster over 5 degrees and have 0 vibe issues at all running down the highway in 4Auto or FAD bypassed.
I am curious as to what is causing your vibes. Do you have a double cardan driveshaft? EDIT: I see now you posted you do have double cardan front shaft. That in itself poses different issues.

Yeah, the dbl cardan shaft is probably the contributor since the spec is supposed to be >1 degree angle alignment with pinion flange. To get that close I’d be way to negative on caster. I don’t wheel at high speed anyway so not a huge issue.

Yes, with 4" of lift on a OEM JL D44 you will need all of the help you can get avoiding vibration.

Yeah, I’ve come to grips with either spending $1950 on the RCV FAD style axles that are obviously a lot stronger than the OEM and possibly trussing the housing or doing a total diff swap.

 

[Jtphoto]

Yeah, the dbl cardan shaft is probably the contributor since the spec is supposed to be >1 degree angle alignment with pinion flange. To get that close I’d be way to negative on caster. I don’t wheel at high speed anyway so not a huge issue.

Yeah, I’ve come to grips with either spending $1950 on the RCV FAD style axles that are obviously a lot stronger than the OEM and possibly trussing the housing or doing a total diff swap.

Have you seen this video. He explains the double cardan angles really well.

 

[Fleeclan]

Have you seen this video. He explains the double cardan angles really well.

He’s definitely entertaining to watch and explains that all well. Tom Woods has a video that is similar but not entertaining. I did go double cardan style shaft because of my lift but hadn’t considered doing the FAD delete.

 

[Jtphoto]

He’s definitely entertaining to watch and explains that all well. Tom Woods has a video that is similar but not entertaining. I did go double cardan style shaft because of my lift but hadn’t considered doing the FAD delete.

I personally had an issue a couple years ago and spend 1/2 a winter in 2wd due to a bad wheel speed sensor. When anyone of the wheel speed sensors go out the FAD will not engage so you have to do it manually. Hence my reason for bypassing the FAD. Either the 392 delete plate, the Dana/Spicer delete or a one piece shaft will do the job.

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