Front Axle Disconnect?

[usmcss]

The driver side is not disconnected, only the passenger side. The front differential is the reason why the ring/pinion gears and front driveshaft don’t rotate. The internal diff gears are spinning instead of the ring/pinion which is the reason the front driveshaft doesn’t spin in 2H. The internal diff gears do rotate the inner half of the passenger axle but it is disconnected from the outer half of passenger axle because the collar shown in the video is offset and not locking the passenger axle halves together. On the TJ and JK everything rotates because it does not have a FAD. The YJ was last wrangler to use FAD.

So why did Jeep return to FAD? Maybe to increase mpg slightly. It puts less wear and tear on the ring/pinion and front drive shaft and their associated bearings and seals. Puts more wear and tear on internal diff gears.

Attached is an illustration on YJ front axle. JL works same way but uses an electric motor instead of vacuum to move the collar. You can see parts 2 & 3 makes up the passenger axle. The collar locks these two parts together. Part 1 is the driver side axle which is one piece.

You could essentially add a FAD to your JK by installing locking front hubs. In theory you would only need one side unlocked to replicate Jeeps FAD design.

This system is used in RAM trucks.

Great info and thank you! But if 1 is one piece on the driverside, then it is still hooked to the wheel and also in the differential, so why doesn't the Driver side (1) make the Drive Shaft move? I would think that the Drive Shaft would need to be disconnected in the Differential. Or disconnected on the passenger side like it is but also on the driver side? What am I missing?

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[Jeepsterfreak]

Great info and thank you! But if 1 is one piece on the driverside, then it is still hooked to the wheel and also in the differential, so why doesn't the Driver side (1) make the Drive Shaft move? I would think that the Drive Shaft would need to be disconnected in the Differential. Or disconnected on the passenger side like it is but also on the driver side? What am I missing?

You are missing how a differential works. The front axles are connected to the internal gears of the differential, not the ring gear. The internal gears (part 8) are spinning inside the diff cage (part 7) but the cage and ring gear (part 15) are not spinning when FAD is on (disconnected).

Have you ever jacked up a vehicle and spun the tire when the transmission is in park or in gear (driveshaft locked)? When you spin one tire clockwise, the opposite tire spins counterclockwise. This is how the differential works. The same thing is happening in the JL front axle. The driver tire and driver axle (part 1) are spinning counterclockwise (forward) causing part 3 (passenger inner axle) to spin clockwise when disconnected.

 

[usmcss]

You are missing how a differential works. The front axles are connected to the internal gears of the differential, not the ring gear. The internal gears (part 8) are spinning inside the diff cage (part 7) but the cage and ring gear (part 15) are not spinning when FAD is on (disconnected).

Have you ever jacked up a vehicle and spun the tire when the transmission is in park or in gear (driveshaft locked)? When you spin one tire clockwise, the opposite tire spins counterclockwise. This is how the differential works. The same thing is happening in the JL front axle. The driver tire and driver axle (part 1) are spinning counterclockwise (forward) causing part 3 (passenger inner axle) to spin clockwise when disconnected.

You are the man Jeepsterfreak! Thank you for the in depth explanation!!! You didn't have to do that and I appreciate it!!!!

 

[on--belay]

The same thing is happening in the JL front axle. The driver tire and driver axle (part 1) are spinning counterclockwise (forward) causing part 3 (passenger inner axle) to spin clockwise when disconnected.

Which is why I’m wondering how shifting into 4H on the fly is going to work now. While it’s often used on my JK at low speeds, I’m wondering if there would be detrimental drivetrain lash on the JL.

 

[Cycleguy]

Would the FAD negate a lunchbox locker so as not to click in 2WD?

 

[mrnoodley]

Would the FAD negate a lunchbox locker so as not to click in 2WD?

It would eliminate the clicking since it won't be engaged in 2WD.

 

[Cycleguy]

Perfect, I was looking for an Elocker for my Dana 30 with 3.45 gears and there are none available, I don't plan on wheeling hard so no lift kit for larger tires, axle swap or re-gearing. The spartan locker with the Fad will make it streetable as a daily driver and much more capable for when I need the 4WD, and the spartan will be more budget friendly. Thanks for your help MRNOODLEY.

 

[bjm00se]

Would the FAD negate a lunchbox locker so as not to click in 2WD?

EDIT - based on replies below, looks like I'm incorrect.
Leaving this reply in place because other folks below have replied to it.

Uh, look at this video, describing how an automatic locker works:



And this one, from earlier in the thread, describing the front axle disconnect:


So, when you're rolling down the road:

1. Passenger axle wheel-side stub is spinning, FAD is open, Passenger axle stub into the differential is NOT spinning
2. Driver side axle is spinning, connected to front diff spider gears

While this means that the front drive shaft is never spinning, it also means that the spider gears are rotating constantly. I haven't torn apart a lunchbox locker, but I think what this means is that it will be spinning constantly, and what you'll have is actually a *maddening and constant* clicking, as if you were constantly driving in a tiny circle.

I've not actually run this experiment, so if I'm missing something, I'll happily delete this post.

 

[mrnoodley]

Uh, look at this video, describing how an automatic locker works:



And this one, from earlier in the thread, describing the front axle disconnect:


So, when you're rolling down the road:

1. Passenger axle wheel-side stub is spinning, FAD is open, Passenger axle stub into the differential is NOT spinning
2. Driver side axle is spinning, connected to front diff spider gears

While this means that the front drive shaft is never spinning, it also means that the spider gears are rotating constantly. I haven't torn apart a lunchbox locker, but I think what this means is that it will be spinning constantly, and what you'll have is actually a *maddening and constant* clicking, as if you were constantly driving in a tiny circle.

I've not actually run this experiment, so if I'm missing something, I'll happily delete this post.

It will be rotating at road speed and the front driveshaft will be spinning (negating the benefits of the FAD), but it won't click since the PS axle shaft is free spinning.

 

[grimmjeeper]

Uh, look at this video, describing how an automatic locker works:



And this one, from earlier in the thread, describing the front axle disconnect:


So, when you're rolling down the road:

1. Passenger axle wheel-side stub is spinning, FAD is open, Passenger axle stub into the differential is NOT spinning
2. Driver side axle is spinning, connected to front diff spider gears

While this means that the front drive shaft is never spinning, it also means that the spider gears are rotating constantly. I haven't torn apart a lunchbox locker, but I think what this means is that it will be spinning constantly, and what you'll have is actually a *maddening and constant* clicking, as if you were constantly driving in a tiny circle.

I've not actually run this experiment, so if I'm missing something, I'll happily delete this post.

A lunchbox locker only ratchets under opposing force from the two axle shafts. And only when you're not applying power from the driveshaft.

So the driver side axle shaft will spin the locker. The inside passenger shaft will spin with the other side. The driveshaft, which is free at the transfer case in 2hi, will spin with the tires.

 

[bjm00se]

Thanks for the clarification. I stand corrected, and learned something!

 

[Holt03]

Hopefully we can buy aftermarket shafts without the disconnect. This seems like something that can easily go wrong on trail. Or at the very least, hot wire it so it's always locked on the connected position.

Theres axle conversion for it.

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