Chasing down vibrations

[JMT]

@PalmettoStateBob. Yes, the rear driveshaft angles are incorrect for a slip yoke. You need a slip yoke eliminator (SYE), double cardan (DC) driveshaft, and rear adjustable control arms.

You have a conventional setup, as shown in the bottom pic of this image.

Once you get an SYE, DC, and adjustable rear control arms, you can set it up like the top photo by changing the length of the rear control arms. Hopefully you got double adjustable arms so you can easily adjust the angle of your pinion so it is pointed directly at the transfer case output shaft as shown in the top photo. The way to check this is to make sure the pinion angle is the same as the driveshaft angle. As mentioned above, it may be slightly better to have the pinion 1* lower than the driveshaft, but either will get you very close and likely be vibe free.

 

[cpwolf]

@PalmettoStateBob. Yes, the rear driveshaft angles are incorrect for a slip yoke. You need a slip yoke eliminator (SYE), double cardan (DC) driveshaft, and rear adjustable control arms.

You have a conventional setup, as shown in the bottom pic of this image.

View attachment 539613
Once you get an SYE, DC, and adjustable rear control arms, you can set it up like the top photo by changing the length of the rear control arms. Hopefully you got double adjustable arms so you can easily adjust the angle of your pinion so it is pointed directly at the transfer case output shaft as shown in the top photo. The way to check this is to make sure the pinion angle is the same as the driveshaft angle. As mentioned above, it may be slightly better to have the pinion 1* lower than the driveshaft, but either will get you very close and likely be vibe free.

@JMT the OP has a 2" lift, and added a MML. With that lift, I don't think a SYE and DC are "Needed" per se, are they? To just get to no vibes and good, shortest path, he already had adjustable arms (and yes, for his sake I hope they are double, ha.).

All he needs to really do is adjust the pinion to be what the lower conventional geometry is at this point. He also put a TC drop, so with the TC and MML, it should really be easy. I would think pull the TC personally, and the 2" lift with a MML and getting the pinion to the conventional in your diagram, there is a good chance vibes will be gone.



Looks like the original "lift" installation and the arms put on, set the pinion really low unnecessarily and that was the start of this issue.

 

[JMT]

@JMT the OP has a 2" lift, and added a MML. With that lift, I don't think a SYE and DC are "Needed" per se, are they? To just get to no vibes and good, shortest path, he already had adjustable arms (and yes, for his sake I hope they are double, ha.).

All he needs to really do is adjust the pinion to be what the lower conventional geometry is at this point. He also put a TC drop, so with the TC and MML, it should really be easy. I would think pull the TC personally, and the 2" lift with a MML and getting the pinion to the conventional in your diagram, there is a good chance vibes will be gone.



Looks like the original "lift" installation and the arms put on, set the pinion really low unnecessarily and that was the start of this issue.

It would help if we knew the “actual” amount of lift. Looking at his driveshaft angles I seriously doubted the lift was only 2”.

Usually on a true 2” lift with vibes a 1” MML or TCase drop will solve the vibes. An SYE/DC/adj rear CA setup is the best (as you know).

 

[cpwolf]

I think my angle is too steep. Thinking axle rotated downward during frame repair.

This^^^^ If the axle is rotated down, you need to adjust it back up to conventional and see if the vibes are corrected. If they don't....then you go on to the next steps.

@JMT mentioned as well, might be worth measuring springs, to make sure it's 2". A 2" really shouldn't need adjustable arms, but since you have them, and did frame repair, the rear pinion needs adjustment.

 

[blamc70]

This^^. In this stock slip yoke drive shaft setup (2 joints) the drive shaft to pinion aren’t the main measure.

The output on TC and Pinion are supposed to match. That Tom Wood’s drive shaft site has a bunch of info on this. Now, the drive shaft angle bh itself looks steep, and that will wear on U Joints.

You can easily test if this is your issue by adding washers at the skid plate, or a full on TC skid drop. It will lower the TC output, easier to match witb pinion, and lessen the DS angle.

That way you can see if this is the item causing issues.

If it were me, I’d pull the front drive shaft, that way you’ve definitely isolated the rear. Get it to no vibes, then add the front, if it changes you know the front is the issue.

More expensive, but better solution. Get a Slip Yoke Eliminator (SYE) Double Cardan driveshaft from Tom Wood’s and adjustable control arms. The SYE and drive shaft will mean you can then use the control arms and the drive shaft angle and pinion would need to be the same (or actually the pinion about 1 degree less than drive shaft is more ideal for axle turn).

Just how I would go about it, others here provided great info

I agree, ds angle is pretty steep, try the TC drop cpwolf suggested. You can use washers, but may need longer bolts. I'd try a 1" drop and see where that leaves you.

 

[PalmettoStateBob]

I agree, ds angle is pretty steep, try the TC drop cpwolf suggested. You can use washers, but may need longer bolts. I'd try a 1" drop and see where that leaves you.

Alright

Recap:
After a 2” lift I picked up a little vibration.
After rear control arm section frame repair I had a very bad vibration. Obviously this repair changed my axle position a little making my DS ^^ steeper causing vibration.
Installed
adjustable upper control arms. Jacked up front of the pinion a little, set DS at 14* ^^, axle and TC are now 1* of each other. Greased U joints, yeah they took grease,
It’s almost as smooth as it was before I did any changes.
I appreciate the help

 

[blamc70]

Alright

Recap:
After a 2” lift I picked up a little vibration.
After rear control arm section frame repair I had a very bad vibration. Obviously this repair changed my axle position a little make my DS ^^ steeper causing vibration.
Installed
adjustable upper control arms. Jacked up front of the pinion a little, set DS at 14* ^^, and TC are now 1* of each other. Greased U joints, yeah they took grease,
It’s almost as smooth as it was before I did any changes.
I appreciate the help

Awesome! Great to hear you got it sorted out!

 

[cpwolf]

Alright

Recap:
After a 2” lift I picked up a little vibration.
After rear control arm section frame repair I had a very bad vibration. Obviously this repair changed my axle position a little making my DS ^^ steeper causing vibration.
Installed
adjustable upper control arms. Jacked up front of the pinion a little, set DS at 14* ^^, axle and TC are now 1* of each other. Greased U joints, yeah they took grease,
It’s almost as smooth as it was before I did any changes.
I appreciate the help

excellent. Let’s go drive ha