JLUR FAD delete kit

[Generoller]

I’m planning to install the Dana Spicer FAD delete kit. Are there any drawbacks or reasons not to do this? I have a tazer as well and ai believe you are supposed to turn FAD off once deleted. Any advice would be appreciated

Sponsored

 

[CarbonSteel]

Just that depending on your caster angle, you may experience vibration at highway speeds. The balance between caster angle and vibration has always been a delicate balance, but with the removal of the FAD it is even more so.

What is the primary reason that you want to remove the FAD?

 

[roaniecowpony]

This topic always interests me. While I've seen, literally, a bunch of FAD housings broken, at a friend's jeep shop, I've never seen the shafts or coupling broken on any forum posts.

 

[Terrymo]

Just that depending on your caster angle, you may experience vibration at highway speeds. The balance between caster angle and vibration has always been a delicate balance, but with the removal of the FAD it is even more so.

What is the primary reason that you want to remove the FAD?

Ok probably a dumb question but why the tendency for vibration at freeway speed on a JL but not a lifted F250 for example?

 

[Jtphoto]

Just that depending on your caster angle, you may experience vibration at highway speeds. The balance between caster angle and vibration has always been a delicate balance, but with the removal of the FAD it is even more so.

What is the primary reason that you want to remove the FAD?

Caster should not be an issue at all. This system is designed to run at highway speed in 4Hi especially if you have 4auto. This idea has been debunked simply by the fact that the 392 and most Wranglers from 2024 up do not have an active FAD. The initial intent of the FAD was fuel economy but it really doesn’t make any difference.
Anyone making driveline modifications should be aware, like on any 4wd vehicle, proper set up and geometry must be addressed to reduce or minimize the chance of vibrations. The FAD is not intended to hide bad set up.
I’ve been around this block a few times. My current JLURXR has 4auto and in 4Auto the FAD stays engaged at all times (like the JK). Lifted on 37s No issues or vibes at highway speeds what so ever.

 

[CarbonSteel]

Caster should not be an issue at all. This system is designed to run at highway speed in 4Hi especially if you have 4auto. This idea has been debunked simply by the fact that the 392 and most Wranglers from 2024 up do not have an active FAD. The initial intent of the FAD was fuel economy but it really doesn’t make any difference.
Anyone making driveline modifications should be aware, like on any 4wd vehicle, proper set up and geometry must be addressed to reduce or minimize the chance of vibrations. The FAD is not intended to hide bad set up.
I’ve been around this block a few times. My current JLURXR has 4auto and in 4Auto the FAD stays engaged at all times (like the JK). Lifted on 37s No issues or vibes at highway speeds what so ever.

I get that, but, caster is always an issue on a lifted Jeep and as I said, it is a balancing act between reducing highway "wander" and vibration. Some Jeeps wander a LOT even when set up properly and adding too much caster will result in vibration as the front driveshaft will undoubtedly turn while driving even in 2H.

As with everything, YMMV...

 

[CarbonSteel]

Ok probably a dumb question but why the tendency for vibration at freeway speed on a JL but not a lifted F250 for example?

The JL series front axles should have had the mounts rotated more than they are because when lifted, it is a battle between caster versus driveshaft angle. Vibration does not always happen particularly at less than a 3.5" lift, but it can be.

Ford does not have that issue.

The OP never said why he wanted to eliminate the FAD, but I agree with @roaniecowpony, the FAD itself is not the weak link, it is the housing and a FAD delete will not circumvent that.

 

[Jtphoto]

It’s been my experience that most people that have driveline vibes are do to swapping out the factory driveshaft with a double cardan driveshaft. People aren’t aware that geometry has to be different with the different style driveshaft to prevent vibration.

 

[grimmjeeper]

The JL series front axles should have had the mounts rotated more than they are because when lifted, it is a battle between caster versus driveshaft angle.

Ford does not have that issue.

In fact, a number of aftermarket manufacturers offer their axles with a rotated pinion. That lets you align the steering properly with the pinion at a better angle to reduce vibration.

 

[Jtphoto]

The JL series front axles should have had the mounts rotated more than they are because when lifted, it is a battle between caster versus driveshaft angle. Vibration does not always happen particularly at less than a 3.5" lift, but it can be.

Ford does not have that issue.

The JK had exactly the same angles.

 

[CarbonSteel]

The JK had exactly the same angles.

Yeah, still does not make it correct. See the post above from @grimmjeeper. If the mount angles were optimum, the aftermarket axle companies would not be changing them. Again, it can be hit or miss, but when the FAD is deleted with a lift kit, vibration is more likely than with the FAD.

 

[grimmjeeper]

It’s been my experience that most people that have driveline vibes are do to swapping out the factory driveshaft with a double cardan driveshaft. People aren’t aware that geometry has to be different with the different style driveshaft to prevent vibration.

Even with the stock driveshaft, the front u-joint is where the vibration comes in. If they had a rzeppa joint at the axle side in the front it wouldn't be as likely to vibrate. But, the fact that the front differential has more travel than the rear, you will over-extend the front joint angle and damage it. The u-joint will take the angle without breaking.

The real way to do it is a double ended double cardan shaft. Or rotate the pinion relative to the steering bits.

 

[grimmjeeper]

The JK had exactly the same angles.

The JL axle may have the same relative angles between the pinion and steering. But if the axle sits lower relative to the transfer case output, the shaft will run at a steeper angle, inducing vibration.

 

[Jtphoto]

Yeah, still does not make it correct. See the post above from @grimmjeeper. If the mount angles were optimum, the aftermarket axle companies would not be changing them. Again, it can be hit or miss, but when the FAD is deleted with a lift kit, vibration is more likely than with the FAD.

Of course, but the FAD was not meant or designed to deal with driveline vibes so using it as such is not a fix. Thats the same argument as using a steering stabilizer to correct steering issues. Fact is you can run 4” lift on a JL with a factory diff no FAD, no vibes and no steering issues.
As to the comment on aftermarket housing with turned Cs, Anyone modifying their vehicle to that point should be aware that it’s not without consequences. You want 5” lift on 40s be prepared to pay.
as for the F250, When they are lifted they also have front driveshaft issues as do the PowerWagons. You can only get away with so much on stock equipment.

 

[CarbonSteel]

Of course, but the FAD was not meant or designed to deal with driveline vibes so using it as such is not a fix. Thats the same argument as using a steering stabilizer to correct steering issues. Fact is you can run 4” lift on a JL with a factory diff no FAD, no vibes and no steering issues.
As to the comment on aftermarket housing with turned Cs, Anyone modifying their vehicle to that point should be aware that it’s not without consequences. You want 5” lift on 40s be prepared to pay.
as for the F250, When they are lifted they also have front driveshaft issues as do the PowerWagons. You can only get away with so much on stock equipment.

Sponsored