Fad delete and rcv axle.

[word302]

The Jeep bean counters disagree. 99% of sales never lift and do serious off road. Now that you can order a Bronco with 37's, Jeep will be forced to offer a 37" package, and the engineers will need to rethink the JMR (next generation).

Meh, they’ll slap 37s on these axles without a 2nd thought.

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[Loctite]

I give up. You’re implying that if you delete the FAD and have vibrations that something is wrong. The only thing wrong is Jeeps poorly designed axle geometry. You can’t have proper caster AND proper pinion angle on lifted JLs and gladiators without going to an aftermarket front axle. The geometry in these axles is different than the JK and TJ. While this is not the reason for the FAD, it’s the only argument for keeping it.

I have a problem with my driveshaft turning when in 2 wheel drive. I have paid an offroad place alot of money to rebuild the differential. Replaced the hub bearing.
affer all that I have a bad loping vibration. It all goes away when I shift it into 4 wheel drive. Jeeps been down all summer.
I am thinking about the FAD eliminate because it is all quiet in 4 wheel drive and I think it isnt completely dis engaging.

 

[word302]

I have a problem with my driveshaft turning when in 2 wheel drive. I have paid an offroad place alot of money to rebuild the differential. Replaced the hub bearing.
affer all that I have a bad loping vibration. It all goes away when I shift it into 4 wheel drive. Jeeps been down all summer.
I am thinking about the FAD eliminate because it is all quiet in 4 wheel drive and I think it isnt completely dis engaging.

If you've got a vibration in 2wd and it goes away in 4wd I doubt it's FAD related.

 

[Loctite]

If you've got a vibration in 2wd and it goes away in 4wd I doubt it's FAD related.

Most everything else has been changed

 

[word302]

Most everything else has been changed

The fact that it goes away in 4wd pretty much rules out the FAD.

 

[Loctite]

The fact that it goes away in 4wd pretty much rules out the FAD.

Actually it rules out that if you delete it you will get vibration.

 

[word302]

Actually it rules out that if you delete it you will get vibration.

I don’t think you really understand how it works

 

[Loctite]

I don’t think you really understand how it works

I was actually baxking up what ypu were saying. I see you just like to be right. Or argue. Or both.

 

[word302]

I was actually baxking up what ypu were saying. I see you just like to be right. Or argue. Or both.

Sorry man, I really wasn’t trying to be an ass. It’s definitely possible to get vibration issues if you delete the FAD unless you swap axles with a better pinion angle to caster relationship. I hope you get it figured out.

 

[Chile1]

Sorry man, I really wasn’t trying to be an ass.

yeah you were.......

 

[Jtphoto]

Of course not, except caster is already low from the factory. Then you start lifting. If you dial your caster in where it should be (around 6.5°) there is a very strong possibility of introducing driveline vibrations. Yes, Jeep failed with the design on these front axles.

The 392 has no FAD and with the XR it has a lift as well … it’s full time 4wd. The Selectrac is also full time AWD when in 4auto the FAD stays connected, I have this and a lift with no driveshaft vibration. I’ve not heard of anyone having driveline vibes from the 392 or Selectrac.

 

[Jtphoto]

The Jeep bean counters disagree. 99% of sales never lift and do serious off road. Now that you can order a Bronco with 37's, Jeep will be forced to offer a 37" package, and the engineers will need to rethink the JMR (next generation).

The only Bronco with 37s is the $130k BRaptor and is no threat to a Wrangler on 35s. The XR can just as easily run 37s if you choose too. No need for Jeep to add them however the AEV upfit for 2024 does have 37s.

 

[Jtphoto]

The fact that it goes away in 4wd pretty much rules out the FAD.

It’s possible the lock sleeve is not fully disengaging in 2wd. So then you have feed back to the transfer case that shouldn’t be there.
If the FAD is fully disengaged you should be able to turn the driveshaft by hand with all wheels on the ground while in 2wd.

 

[Jtphoto]

The fact that it goes away in 4wd pretty much rules out the FAD.

In 2wd with the FAD disconnected the only thing in the front end that can vibrate is the wheel bearings, and the carrier bearing on the driver side. However, It is possible that the bushing that centers the passenger side stub axle in the center axle is worn. While engaged the collar holds it tight but while disengaged the stub axle could be flopping around.

 

[Fleeclan]

My point (which I think is also yours) is that if you have vibration it is likly due to a bad pinion angle or an un-balanced driveshaft and adding a FAD is not the solution to get rid of it and is not the reason why they added the FAD to the JL design. Also, taking away the FAD from a good pinion angle and balanced driveshaft is not going to add vibration.

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.

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