Bad Vibration after Front Driveshaft Install

[WILDHOBO]

So is the reason the OEM shaft doesn’t vibrate is because of the CV joint at the TC? Because the OEM style is a 1300 series joint at the axle and CV at the TC. And wouldn’t the CV just get tore up at the axle side due to the angles?

I don’t know for sure, but I’d think a cv joint exists that can handle those angles. My cv axle shafts certainly can handle angles at high speeds.

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[JTenn]

So is the reason the OEM shaft doesn’t vibrate is because of the CV joint at the TC? Because the OEM style is a 1300 series joint at the axle and CV at the TC. And wouldn’t the CV just get tore up at the axle side due to the angles?

A CV style joint has more points of contact which distributes the load across a larger contact area thus allowing for greater angular rotation. The CV's have hardened ball bearings that ride in radiused tracks. The balls naturally follow the tracks as the joint rotates through its angle if the joint is in an angled condition. The point is more angular contact = smoother motion because the motion is distributed over a larger area.

 

[ShadowsPapa]

A CV style joint has more points of contact which distributes the load across a larger contact area thus allowing for greater angular rotation. The CV's have hardened ball bearings that ride in radiused tracks. The balls naturally follow the tracks as the joint rotates through its angle if the joint is in an angled condition. The point is more angular contact = smoother motion because the motion is distributed over a larger area.

CV is constant velocity.
Yes, they can handle greater angles, but the larger part is that there is no velocity change while the parts rotate.

If you take a look at the end of a shaft with a ujoint from the end, you'll see that it doesn't travel in a circle at all.
It moves in an ellipse. That means that it has to speed up and slow down because although all parts have to make the voyage around at the same time, some are moving in a "smaller circle" part of the time, then back out to a larger circle. So it has to speed up and slow down.
The more the angle, the greater the change in speed.

Here's a picture I stole rather than trying to draw it with my hands as they are -

Note that at a 30 degree angle (extreme, I know) the part being driven has to change this much - twice. Slow, speed, slow, speed, two times a revolution.

 

[JTenn]

CV is constant velocity.
Yes, they can handle greater angles, but the larger part is that there is no velocity change while the parts rotate.

If you take a look at the end of a shaft with a ujoint from the end, you'll see that it doesn't travel in a circle at all.
It moves in an ellipse. That means that it has to speed up and slow down because although all parts have to make the voyage around at the same time, some are moving in a "smaller circle" part of the time, then back out to a larger circle. So it has to speed up and slow down.
The more the angle, the greater the change in speed.

Here's a picture I stole rather than trying to draw it with my hands as they are -

Note that at a 30 degree angle (extreme, I know) the part being driven has to change this much - twice. Slow, speed, slow, speed, two times a revolution.

Yeah, that's what I was tryin to say. Lol thanks for the clearer explanation. I didn't have the time to grab all the pics. But thats the reason the double Carden joint works. It splits all the elliptical movement in half and distributes the points of contact over 8 points instaed of 4. I completely understand all the physics involved.

 

[Billyj7175]

I'm late to the party, but have a similar situation;
3.5" MetalCloak lift , running an Adam's front driveshaft, with the factory FAD delete (2023 Rubi JT with the 4-Auto optioned T-Case). The shop that did the work took a couple of tries, but they got the vibration pretty minimal. I'll have to check my paperwork to see where my caster was at.
However, I do still get a slight vibration at 65mph. It comes on about 62, and is strongest at 65 and goes away about 68.
Regardless, any vibration is detrimental over time, so my concerns are still there about the longevity of the u-joints, pinion and t-case output bearing & seals.

 

[WILDHOBO]

I'm late to the party, but have a similar situation;
3.5" MetalCloak lift , running an Adam's front driveshaft, with the factory FAD delete (2023 Rubi JT with the 4-Auto optioned T-Case). The shop that did the work took a couple of tries, but they got the vibration pretty minimal. I'll have to check my paperwork to see where my caster was at.
However, I do still get a slight vibration at 65mph. It comes on about 62, and is strongest at 65 and goes away about 68.
Regardless, any vibration is detrimental over time, so my concerns are still there about the longevity of the u-joints, pinion and t-case output bearing & seals.

What joints on your Adam’s? Single or double cardan at the t case?

 

[WILDHOBO]

I'm late to the party, but have a similar situation;
3.5" MetalCloak lift , running an Adam's front driveshaft, with the factory FAD delete (2023 Rubi JT with the 4-Auto optioned T-Case). The shop that did the work took a couple of tries, but they got the vibration pretty minimal. I'll have to check my paperwork to see where my caster was at.
However, I do still get a slight vibration at 65mph. It comes on about 62, and is strongest at 65 and goes away about 68.
Regardless, any vibration is detrimental over time, so my concerns are still there about the longevity of the u-joints, pinion and t-case output bearing & seals.

Thankfully you can just only put it in 4hi auto when it’s slippery. That’s what I do.

 

[Billyj7175]

Thankfully you can just only put it in 4hi auto when it’s slippery. That’s what I do.

Its a double at the t-case.

Unfortunately, since the front spins all of the time, my vibrations are always there, regardless of being in 2wd or 4-auto.

 

[WILDHOBO]

Its a double at the t-case.

Unfortunately, since the front spins all of the time, my vibrations are always there, regardless of being in 2wd or 4-auto.

The front driveshaft doesn’t rotate with 4hi auto t cases, if you’re in 2wd. Unless it’s the t case that comes with the 392.

 

[Billyj7175]

The front driveshaft doesn’t rotate with 4hi auto t cases, if you’re in 2wd. Unless it’s the t case that comes with the 392.

I surely can't account for others, but mine didn't have a FAD from the factory. It had the coupler lockout plate, like the 392's. So yes, mine turns all of the time.

However, it still has the 2wd option. So it has 2wd, 4-Auto, 4-Hi, 4-Low.

I went with the one piece RCV's, so it's now removed.

 

[ShadowsPapa]

I surely can't account for others, but mine didn't have a FAD from the factory. It had the coupler lockout plate, like the 392's. So yes, mine turns all of the time.

However, it still has the 2wd option. So it has 2wd, 4-Auto, 4-Hi, 4-Low.

I went with the one piece RCV's, so it's now removed.

You are saying you have The Rock-Trac automatic transfer case - the Rubicon version of the Selec-Trac others might have?
Of course you are - I see you said you have 4Hauto as well as 4H

This must be how they handle the fact that when in 4H auto, the clutches are engaged from a stop up to about 15 mph or so much throttle percentage, but they release as you pick up speed, then engage again if you mash the throttle. Otherwise a FAD would be kicking in and out so fast it would be crazy.

So in that case, yes, the front shaft turns at all times.

So there we have it - my suspicions on the Selec-Trac (and Rubicon Rock-Trac automatic) is confirmed - the FAD was locked engaged on the automatic transfer cases. So it doesn't matter WHAT position that transfer case is in, if you have the 4H auto position on your shifter, you have a FAD locked engaged at all times and your front shaft always spins - thus, the vibrations.

That's why some experience it, others don't so much.

 

[Billyj7175]

That's why some experience it, others don't so much.

Yes sir.

The other difference was the stock front axle shafts have a CV style joint at the knuckle instead of a conventional u-joint.

I had no idea about what I was getting into when I bought it. I wasn't really in the market for one, until the 2023 close out deals started last year. It's an oddly equipped Rubicon though; it had no factory front camera, no FAD, and no aux switches, but had leather seats.

 

[ShadowsPapa]

Yes sir.

The other difference was the stock front axle shafts have a CV style joint at the knuckle instead of a conventional u-joint.

I had no idea about what I was getting into when I bought it. I wasn't really in the market for one, until the 2023 close out deals started last year. It's an oddly equipped Rubicon though; it had no factory front camera, no FAD, and no aux switches, but had leather seats.

Having the automatic transfer case - Rock-Trac Automatic, as it's called for the Rubicon, explains the CV axle joints and locked-in FAD.
Since you are always turning the front wheels under some load with the FAD locked, you'd feel jerking motions with regular u-joints up there.

The rest is an interesting combo.

 

[hjdca]

Note: Because of the size, 1350 driveshafts are known to vibrate at less of an angle than 1310 driveshafts. I would decrease the pinion angle slightly, (shorten LCAs, lengthen UCAs), thus, unfortunately decreasing the caster, to see if I could make it go away and still get nice tracking at speed. Some fine tuning like that may fix it.

 

[ShadowsPapa]

Because of the size, 1350 driveshafts are known to vibrate at less of an angle than 1310 driveshafts.

Makes sense - the 1350 max angle is 20 degrees compared to the max angle of the 1310 at 30 degrees.
Wider joints will mean a larger rpm change because the orbit change is increased.

The only choices are a different joint - CV or a less strong joint, or reduce caster.
for those of us with front shafts that always turn - even in 2H at highway speeds, you have to give up something.

("Select-trac" and "Rock-Trac Automatic" mean that front shaft is always rotating, and going the same speed as the rear shaft is at 70 mph)

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