Adams drive shaft - required?

[Remorseless]

Genuinely asking - what does FAD have to do with caster and pinion angle?

With a FAD your front driveshaft does not spin in two wheel drive. This means you can run a much more aggressive caster angle (not great pinion angle) and thus get the steering benefits of aggressive caster. Without the FAD, even though the front driveshaft isn't connected to the engine's power via the transfer case, it still spins when in two wheel drive. This means that pinion angle must be squared away or the front driveshaft will vibrate something awful just cruising down the road. Pinion angle and caster have to be balanced for the Jeep to steer well without a vibration, but the angles on the JL axles seem to make that hard when there's no FAD present.

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[ym0bc1]

I’m just a hobbiest but I will try to explain. The benefit of the FAD is that the front driveshaft does not spin when your jeep is in 2WD, without it, we’re in full time 4WD (2024+ wranglers and all 392 have this design, and anyone else who has purposefully deleted it).

When you have a traditional U Joint style driveshaft, like most aftermarket driveshafts, you need the pinion angle to be pointing toward the transfer case flange such that the double carden does not rotate about any other axis than the transfer case interface axis. The more this angle is off, the more driveline vibration you feel. The kicker is that to achieve this, with most stock axles, you have to have lower than desired caster to avoid bad road manners (because you have to tilt the axle so far forward, lowering your caster.

This is why aftermarket housings offer rotated C’s, and previous Jeep generations people would cut and rotate C’s.

When the FAD does its job, the driveshaft won’t rotate when at highway speeds so you don’t really get the vibration effect. You can cheat and favor desirable caster angle over the ideal pinyon angle.

I and wondering if we will start to see more cut and turns in ‘24+ JLs. I am considering doing it depending on how well I can balance pinyon and caster angles when my driveshaft arrives

I see what you meant. Thanks.

This leads to another recent confusion I had.
I was also under the impression that front driveshaft will not spin when having an FAD and at 2WD.
Yesterday, I attached my camera under the body, and recorded it. The driveshaft did not spin in the first 3-5 seconds, and shortly after it started spinning, at 2WD. @Remorseless . Any idea? Or the FAD operates at certain speed? I was recording it in the parking lot.

 

[Remorseless]

I see what you meant. Thanks.

This leads to another recent confusion I had.
I was also under the impression that front driveshaft will not spin when having an FAD and at 2WD.
Yesterday, I attached my camera under the body, and recorded it. The driveshaft did not spin in the first 3-5 seconds, and shortly after it started spinning, at 2WD. @Remorseless . Any idea? Or the FAD operates at certain speed? I was recording it in the parking lot.

That shouldn't happen.

 

[JEEP4U]

Adam's???

Spicer produces their own 1350 version for the Jeep JLU.

You know Adam's utilize Spicer parts to build their driveshafts

I have been running my Spicer 1350 shafts now for 4 years..... No issues

 

[CO2Wrangler]

Adam's???

Spicer produces their own 1350 version for the Jeep JLU.

You know Adam's utilize Spicer parts to build their driveshafts

I have been running my Spicer 1350 shafts now for 4 years..... No issues

Got a link?

 

[GATORB8]

Got a link?

Northridge carries them.

 

[ym0bc1]

Adam's???

Spicer produces their own 1350 version for the Jeep JLU.

You know Adam's utilize Spicer parts to build their driveshafts

I have been running my Spicer 1350 shafts now for 4 years..... No issues

It doesn't really matter who makes them, as long as they use good u-joint, like spicer or neapco. Building a driveshaft isn't like building a rocket.
Any local driveline shop can do it, and sometimes it's better quality (material, balancing, welding).

 

[RickyPal]

I see what you meant. Thanks.

This leads to another recent confusion I had.
I was also under the impression that front driveshaft will not spin when having an FAD and at 2WD.
Yesterday, I attached my camera under the body, and recorded it. The driveshaft did not spin in the first 3-5 seconds, and shortly after it started spinning, at 2WD. @Remorseless . Any idea? Or the FAD operates at certain speed? I was recording it in the parking lot.

I wonder if your mechanism is failing and it engages in some sort of default fail safe. I bet it would throw a light though?

 

[AnnDee4444]

Right at 6. Pinion is right at 0. Going to 7-8 would make the problem worse not better.

Do you have lower control arm drop brackets? I could see how they would cause the pinion angle change during droop to be different than OEM.

 

[BradyW]

Wanted to add a data point to this discussion for future searchers.

3.5” lift on a 2024 rubicon XR 3.6 AT running billstein 5100 (24-310635) which are marketed as a 28.4” extended length shock

Bent the flange pretty good and tore the boot despite being under 29” extended length.

Ordering an Adam’s this weekend, but now the JLs do not come with FAD so I will have to play the game of balance castor and pinyon angle

I'm planning on purchasing an aftermarket front driveshaft for my lift, but I was wondering... Has anyone cut the flange off that part of the drive shaft with an angle grinder? It doesn't appear to be doing much other than getting bent and destroying the boots of the poor joints.

 

[Nokones]

Tom Woods are also a quality product. Make sure you get the 1350 joints and also make sure your pinion angles don't exceed more than 2 degrees in relationship to your shafts.

More than likely, you will need to add adjustable bars and arms, if you haven't already.

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