How far is the output shaft in the slip yoke when installed? 1”, 2”?
Well, if I'm still not totally sure what you meant, but I did take this picture.

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Sorry if this is the wrong thing, I can take a new picture if it is.

X2, the pinion angle needs to stay parallel to the output shaft angle when you're still running the factory rear driveshaft. Like this...

View attachment 376633

The rear pinion angle should not be changed when the factory driveshaft is still installed
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Here are more measurements, again, hoping I got the right stuff. I'm assuming these are out of tolerance. Seeing that the t-case and rear axle are 7 degrees different, I am assuming I need to bite the bullet and just get the arms and SYE kit if I want to do it the right way.
 
Or does that mean that the driveshaft isn't the issue here?
It implies that the angles are ok.
Could still be an issue with joints, yokes, etc.
Have you tried to eliminate the vibe with a TC drop?
Did you ever drive it with the rear driveshaft out?

So in your opinion, the SYE wouldn't be worth it?
An SYE can be a rabbit hole.
You have to decide if it's worth it.
Can you tolerate it as is?
How do you plan to use it?
How long do plan to keep it?
 
@ThomasFletch. This only happens under high torque when you start for like a second. I’d move on. If you are OCD get an SYE, DC and rear Ca’s. It’ll only cost $1500 if you install it yourself.

$750 rear CA’s
$350 SYE
$400 DC

However, what I really think you should do is buy about 30 washers and add 5 to each skid plate mount to drop the TCase about 1/2”. Then go for a drive and see if it goes away.
 
It implies that the angles are ok.
Could still be an issue with joints, yokes, etc.
Have you tried to eliminate the vibe with a TC drop?
Did you ever drive it with the rear driveshaft out?
I did try the T-case drop, but it wasn't low enough, I think. Did the uneven yoke wear I had in an earlier picture seem strange to you, or is that normal? Could something in the rear diff cause anything similar to this? I did drive without the shaft, and I couldn't replicate the shudder, but I would just do burnouts instead on accident.

Can you tolerate it as is?
How do you plan to use it?
How long do plan to keep it?
I think I can tolerate it, like @JMT said for OCD's sake I think would really be the only reason I would fix it, as there appears to be no damage or wear on anything. This is my daily, and weekend toy, so probably for a while. Every time something comes up, I think about selling it for a Tacoma or something, but then I look at everyone else's builds and the various threads on here and change my mind. My relationship with the Jeep is definitely love/hate, but at the end of the day, it has never left me stranded of its own accord, only if I did something stupid to it beforehand.

This only happens under high torque when you start for like a second. I’d move on. If you are OCD get an SYE, DC and rear Ca’s. It’ll only cost $1500 if you install it yourself.

$750 rear CA’s
$350 SYE
$400 DC

However, what I really think you should do is buy about 30 washers and add 5 to each skid plate mount to drop the TCase about 1/2”. Then go for a drive and see if it goes away.
Knowing that you have this same problem with your Jeep and the other 2" one you said you are working on and didn't have issues, I think I will leave it. The more I think back on this, the more I'm pretty sure I've had this since my lift was installed a year ago and never really thought twice about it. I've gone on multiple trails here in my local mountains, harder trails in the area, jumped it a few times, and may have gotten it stuck in the mud all the way past the frame… (Profile picture was the first time with no lift) Over these two years, I never had any issues with it. And now seeing that @LONGJP2 is saying my angles seem to be ok, and you, reminding me it only happens for a second, I think I will move on like you said. I may do the washers just for my own piece of mind. If anything catastrophic happens, I will be sure to post either on this thread or make a new one entirely.

Again, thank you everyone for all your help on this!
 
I am no where near the expert on lifts and drivetrain vibes, but I think you should look again at the slip yoke. You were asking questions about it and how it is worn. Someone upstream asked about how much engagement. this is asking how far does the yoke on the driveshaft slide over (engage) the splines in the back to the tcase. The wear pattern looks like it's only going in and inch or so (hard to tell). If that's the case, it certainly could move around and cause vibes. You *may* need a longer driveshaft.

I add this comment to add fuel to others who know more about this than me....

edited to add: If you do find this is an issue and decide to replace the driveshaft, there should be a bushing in the back of the tcase that the driveshaft yoke rides on. I'd replace this at the same time.
 
[...]how much engagement. this is asking how far does the yoke on the driveshaft slide over (engage) the splines in the back to the tcase. The wear pattern looks like it's only going in and inch or so (hard to tell). If that's the case, it certainly could move around and cause vibes. You *may* need a longer driveshaft.
I will take a look and report back. When you say new driveshaft, do you mean one of the same type? And by bushing, are you talking about the rubber boot or something entirely different?
 
I will take a look and report back. When you say new driveshaft, do you mean one of the same type? And by bushing, are you talking about the rubber boot or something entirely different?
Driveshaft: Yes, I'm thinking the same type but a little longer. Your vibrations might be caused by the fact that your driveshaft isn't engaging the tcase output shaft deep enough. This could be a result of the lift. Now, does a suspension lift move the axle closer or further from the tcase? I dunno.

Bushing: I'm talking about a bronze bushing that is likely pressed into the tailcone of the tcase where the driveshaft slides in. The outside of the yoke (outside smooth part, splines are in the inside) would ride on this. I don't know whether or not this bushing exists in our tcases, but the tailcones on transmissions I'm familiar with do have them.

Someone will hopefully chime in about what I'm talking about above to let us know if any of it makes any sense, as it's more conjecture than fact at this point. Also, the FSM would tell us whether or not the bushing exists. I'm too lazy to look it up right now though.

EDIT!

Ok, I didn't see the pictures.

BUSHING: It doesn't apply here, forget about this.

DRIVESHAFT: That should be plenty of engagement, so driveshaft length isn't an issue either.

Another thing that could be going on is that the yoke splines are worn and are causing vibrations.

Otherwise, I'd continue with the experiments above, ie, lowering the skid with washers to see if this resolves your issue.
 
BUSHING: It doesn't apply here, forget about this.

DRIVESHAFT: That should be plenty of engagement, so driveshaft length isn't an issue either.

Another thing that could be going on is that the yoke splines are worn and are causing vibrations.

Otherwise, I'd continue with the experiments above, ie, lowering the skid with washers to see if this resolves your issue.
Roger that. I appreciate the input!
 
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Driveshaft: Yes, I'm thinking the same type but a little longer. Your vibrations might be caused by the fact that your driveshaft isn't engaging the tcase output shaft deep enough. This could be a result of the lift. Now, does a suspension lift move the axle closer or further from the tcase? I dunno.

Bushing: I'm talking about a bronze bushing that is likely pressed into the tailcone of the tcase where the driveshaft slides in. The outside of the yoke (outside smooth part, splines are in the inside) would ride on this. I don't know whether or not this bushing exists in our tcases, but the tailcones on transmissions I'm familiar with do have them.

Someone will hopefully chime in about what I'm talking about above to let us know if any of it makes any sense, as it's more conjecture than fact at this point. Also, the FSM would tell us whether or not the bushing exists. I'm too lazy to look it up right now though.

EDIT!

Ok, I didn't see the pictures.

BUSHING: It doesn't apply here, forget about this.

DRIVESHAFT: That should be plenty of engagement, so driveshaft length isn't an issue either.

Another thing that could be going on is that the yoke splines are worn and are causing vibrations.

Otherwise, I'd continue with the experiments above, ie, lowering the skid with washers to see if this resolves your issue.
A couple of things here.

1) the distance is farther between pinion and TCase output after a lift.

2) the splines can be worn and cause a vibration. Test by firmly grabbing rear shaft and pushing and pulling strongly to see if there is any play (not sliding it)

3) if you’ve re-geared and the shaft is spinning faster than 3000rpm at 70mph then you may get a vibe if it’s not balanced good enough (doesn’t apply to this situation.

Since this is on take-offs only, lower the TCase a full 1/2” and test it. This other stuff is not your issue IMHo.
 
Everything I've read on here is good advice and input. I agree, the angles don't seem to be the issue here and do not seem to necessitate an SYE and double cardan shaft. You might still benefit from it but perhaps only due to the fact that you'd be replacing a bunch of old things with new things. The shudder might be coming from something else entirely.

Since there is much discussion about angles, and proper angles for the stock shaft, I'd like to introduce a new video I found the other day to the forum. We have a similar video which covers this more specifically to a Jeep application but this guy's video in many ways is better than the video we produced. I think it may be the best all-around drive shaft angle explanation video I've seen. Enjoy: