FAD Missing

[JeepOfTheseus]

Cracks me up every time I see someone post up another "upgrade". Some items truly are, but not everything needs to be swapped out.

I don't disagree with the overall sentiment towards upgrading unnecessary things (and/or making things worse than stock). I felt like I was very close (if not at) the limit of the Rzeppa joint, especially up front. That said, I did jump the gun a bit (and honestly: it was mostly because of the sale @Northridge4x4 was having).

I also thought I'd "get ahead" of any premature wear/failure due to the 37" wheels, and was convinced that 1350 axles weren't a dumb idea. Unfortunately, I didn't do quite enough research to realize the Dana axles require FAD delete. I still pushed forward and figured it wouldn't contribute a significant amount of vibration if the front driveshaft isn't engaged (since it's basically spinning freely and not under torque from the TC) - in fact, a local shop made the same claim. That was very wrong.

It's 100% caused by people's lack of understanding the different joint types.

I'm not an expert, but that was one area I did research, and I did understand the risks/requirements of switching to u-joint/double cardan joints. I knew the pinion angle needs to be effectively straight, which means the front can't ever really be straight due to caster. But again...I didn't think/realize that would be an issue in 2WD.

These discussions are the thoughts that have drove me (among other reasons) to not modify the Gladiator as heavily as I did my JK.

That's exactly why I shared all of my experience...even though the end result was going back to stock. I don't know how some folks are doing it, but at the end of the day...I have first-hand experience that:

• FAD delete will absolutely cause vibration (especially with a double cardan joint), even in 2WD. And caster angle is always going to win the battle here unless you like wandering.
• Single piece rear driveshaft with double cardan joint is difficult (if not impossible) to avoid vibrations with. My pinion angle was pointed straight at the driveshaft, and I still got vibrations at 70+ mph. That was with the front driveshaft uninstalled entirely. I don't know if it's the length, the joints, or both...but I had two driveshafts and they both did the same thing.
• Going back to stock front axles and front/rear driveshafts (still have 1350 rear axles) eliminated the vibration for me (even though my rear pinion angle hasn't been brought back down yet).

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[CrazyCooter]

I don't disagree with the overall sentiment towards upgrading unnecessary things (and/or making things worse than stock). I felt like I was very close (if not at) the limit of the Rzeppa joint, especially up front. That said, I did jump the gun a bit (and honestly: it was mostly because of the sale @Northridge4x4 was having).

I also thought I'd "get ahead" of any premature wear/failure due to the 37" wheels, and was convinced that 1350 axles weren't a dumb idea. Unfortunately, I didn't do quite enough research to realize the Dana axles require FAD delete. I still pushed forward and figured it wouldn't contribute a significant amount of vibration if the front driveshaft isn't engaged (since it's basically spinning freely and not under torque from the TC) - in fact, a local shop made the same claim. That was very wrong.



I'm not an expert, but that was one area I did research, and I did understand the risks/requirements of switching to u-joint/double cardan joints. I knew the pinion angle needs to be effectively straight, which means the front can't ever really be straight due to caster. But again...I didn't think/realize that would be an issue in 2WD.



That's exactly why I shared all of my experience...even though the end result was going back to stock. I don't know how some folks are doing it, but at the end of the day...I have first-hand experience that:

• FAD delete will absolutely cause vibration (especially with a double cardan joint), even in 2WD. And caster angle is always going to win the battle here unless you like wandering.
• Single piece rear driveshaft with double cardan joint is difficult (if not impossible) to avoid vibrations with. My pinion angle was pointed straight at the driveshaft, and I still got vibrations at 70+ mph. That was with the front driveshaft uninstalled entirely. I don't know if it's the length, the joints, or both...but I had two driveshafts and they both did the same thing.
• Going back to stock front axles and front/rear driveshafts (still have 1350 rear axles) eliminated the vibration for me (even though my rear pinion angle hasn't been brought back down yet).

So, I can see a possible 1350 CV rear shaft in my future UNLESS it's going to vibrate because I have zero tolerance for that nonsense. In that case, may cough up for another OE shaft.

Did you verify the front half of the shaft was set at the proper angle ofpr just trust the carrier bracket set it correctly out of the box? Ideally the first shaft will be the same as the crankshaft/output shaft centerline. Anything more or less will have the shaft speed oscillating every 90° and cause a potential vibration.

For the second shaft, the double cardan joint will cancel itself out, and the 0° angle at the pinion will obviously be stationary EXCEPT that the OE control arm geometry has the pinion changing quite a bit as the suspension travels. Is this your issue?

I only have experience with a 1pc 1350 CV shaft before anyone had a 2pc solution. It didn't vibrate, but it did amplify gear noise through it. For ground clearance reasons, I'd prefer a 2pc personally even though it will probably be heavier.

 

[JeepOfTheseus]

Did you verify the front half of the shaft was set at the proper angle ofpr just trust the carrier bracket set it correctly out of the box? Ideally the first shaft will be the same as the crankshaft/output shaft centerline. Anything more or less will have the shaft speed oscillating every 90° and cause a potential vibration.

For the second shaft, the double cardan joint will cancel itself out, and the 0° angle at the pinion will obviously be stationary EXCEPT that the OE control arm geometry has the pinion changing quite a bit as the suspension travels. Is this your issue?

I only have experience with a 1pc 1350 CV shaft before anyone had a 2pc solution. It didn't vibrate, but it did amplify gear noise through it. For ground clearance reasons, I'd prefer a 2pc personally even though it will probably be heavier.

Not sure if I misspoke somewhere, but mine was a single piece. I had the pinion facing within a degree of the driveshaft. And that was something that always made me cringe: hitting a whoopdie at 70 mph and putting it way off angle was a feeling I never got used to.

 

[CrazyCooter]

Not sure if I misspoke somewhere, but mine was a single piece. I had the pinion facing within a degree of the driveshaft. And that was something that always made me cringe: hitting a whoopdie at 70 mph and putting it way off angle was a feeling I never got used to.

I may have missed or misread yours was a 1pc. In that case........is it possibly operating at, near, or 1/2 of critical speed? That's a long shaft and things can get weird.

 

[JeepOfTheseus]

I may have missed or misread yours was a 1pc. In that case........is it possibly operating at, near, or 1/2 of critical speed? That's a long shaft and things can get weird.

That’s where I probably didn’t do enough research. I assumed because they sold it, that it should be fine. Here’s what’s interesting (to me) - they don’t carry it anymore…

 

[CrazyCooter]

That’s where I probably didn’t do enough research. I assumed because they sold it, that it should be fine. Here’s what’s interesting (to me) - they don’t carry it anymore…

Well.......generally if it's not available anymore, it either didn't sell OR it sucked?

When I did the 1pc at the shop for the client in 2020, it was the only thing available other than OEM. I now wish I had kept his damaged shaft for parts!

 

[WILDHOBO]

So, I can see a possible 1350 CV rear shaft in my future UNLESS it's going to vibrate because I have zero tolerance for that nonsense. In that case, may cough up for another OE shaft.

Did you verify the front half of the shaft was set at the proper angle ofpr just trust the carrier bracket set it correctly out of the box? Ideally the first shaft will be the same as the crankshaft/output shaft centerline. Anything more or less will have the shaft speed oscillating every 90° and cause a potential vibration.

For the second shaft, the double cardan joint will cancel itself out, and the 0° angle at the pinion will obviously be stationary EXCEPT that the OE control arm geometry has the pinion changing quite a bit as the suspension travels. Is this your issue?

I only have experience with a 1pc 1350 CV shaft before anyone had a 2pc solution. It didn't vibrate, but it did amplify gear noise through it. For ground clearance reasons, I'd prefer a 2pc personally even though it will probably be heavier.

For the rear, i can’t recommend the two piece Adam’s enough. No vibration with a 6.5” lift and it stays balanced even after occasional rock hits.

 

[WILDHOBO]

Not sure if I misspoke somewhere, but mine was a single piece. I had the pinion facing within a degree of the driveshaft. And that was something that always made me cringe: hitting a whoopdie at 70 mph and putting it way off angle was a feeling I never got used to.

One piece driveshafts for the gladiator are just too long. The only way to keep the angle straight into the transfer case is with a two piece. It just took the aftermarket a long time to come up with rear two piece shafts. Some still don’t.

 

[WILDHOBO]

I may have missed or misread yours was a 1pc. In that case........is it possibly operating at, near, or 1/2 of critical speed? That's a long shaft and things can get weird.

Too long, too heavy.

 

[JeepOfTheseus]

It just took the aftermarket a long time to come up with rear two piece shafts. Some still don’t.

Biggest regret was not waiting for this.

 

[WILDHOBO]

Biggest regret was not waiting for this.

My second driveshaft was the Dana heavy duty two piece. It was better than stock, but not as good as Adam’s. Back then, everyone laughed at me for having the two piece. I make lots of boneheaded decisions, but that just made sense.

 

[Rusty PW]

What gets me. On my Power Wagon. The rear driveshaft was one piece that was longer than what's on the JT. The front driveshaft had a u joint with a cardan joint with a steeper angle because of the 4" lift. No FAD on the front axle, with no vibrations. I can't wrap my head around this. There have been reports of aftermarket driveshafts been out of balance right out of the box. Wondering if the driveshafts are out of phase some what too.

 

[WILDHOBO]

What gets me. On my Power Wagon. The rear driveshaft was one piece that was longer than what's on the JT. The front driveshaft had a u joint with a cardan joint with a steeper angle because of the 4" lift. No FAD on the front axle, with no vibrations. I can't wrap my head around this. There have been reports of aftermarket driveshafts been out of balance right out of the box. Wondering if the driveshafts are out of phase some what too.

Is the pinion angle higher on the PW?

 

[Rusty PW]

Is the pinion angle higher on the PW?

Can't answer that.

 

[Rusty PW]

Is the pinion angle higher on the PW?

I've watched videos where people have replaced their driveshafts on their JT's and no mention of vibrations. That's what got me scratching my head.

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