Driveshaft angle question

I have a stock two piece driveshaft that I had modified with a double cardan joint after the carrier bearing. I am still getting some takeoff shakes and vibrations on the highway. With my driveshaft setup do the output shaft and pinion joints have to be the same angle or do I just need to adjust the pinion angle so it is straight in line with the driveshaft?

 

Subd, looking for same advice on my 1st gen which has the above DS config. from the factory. Raised the rear end ~2.5" (more like 3") with OME/ARB Dakar leaf springs and have vibration at highway speeds. Unfortunately I did not measure any angles from stock prior to rebuilding my rear end.

Progression:

1. Added Toytec 3° shims to tilt the pinion up and point at the DC-joint/CB --> still has vibes
2. Replaced entire DS w/ USA STD GEAR DS from rock auto --> still has vibes and gained additional noise under load (sounds similar to a bad bearing)
3. Spaced the CB so that TC/Drive and Pinion u-joint angles were the same (~2°) --> still has vibes and noise

I've searched within and outside this forum extensively and can't seem to find a definitive answer on this exact DS configuration. Not exact angle numbers, just relationship between them.

Here are the different configs. as I understand them currently (please correct if wrong).

1. 1-Piece (conventional) DS w/ single-cardan joint at each end --> Drive and pinion should be at same angle creating a parallelogram.
2. 2-piece DS w/ 3 single-cardan joints & CB --> 2 joint angles should cancel and the 3rd close to zero.
3. 1-Piece DS w/ double-cardan joint at drive flange --> Angle the pinion up to be inline with the shaft and point at the double-cardan joint.
4. 2-Piece DS w/ double-cardan joint between two shafts (after CB) and single-cardan joints at drive and pinion flanges. --> ???

Since my last effort of matching the end u-joint angles while still pointing the pinion up at the double cardan didn't work, my next logical guess is to remove my 3° shims and maybe even put them in backwards to try and get the TC/drive and pinion aligned at the same angle and space CB so the end u-joint angles are close as well? I've also seen recommendations to aligning the pinion with the 1st shaft instead of the TC/drive flange.

As someone else on here stated "the double cardan joint really messes with the napkin math on this one".
Btw, I am new to this forum. Any help with this is greatly appreciated!

-Stevo

 

From what I understand, with a 2 piece DS that has a double cardan joint after the carrier bearing the only measurement that we need to play with is the u joint on the rear pinion end. The ujoint on the output shaft and the cardan joint will cancel each other out. You want to get the driveshaft slope and the pinion u joint almost in a strait line with minimal ujoint "working angle".

 

Hey Hennessy3300, I believe I'm currently pretty close to what you're describing.
I took a bunch of measurements and modeled my driveline in SolidWorks. All the bottom angles are relative to the TC output shaft. Top diagram is where I was after the 3° shims and no CB spacer. Last night, I rotated the CB 180° bringing it higher and then added a 0.5" spacer. Effectively the CB moved up 0.2" (bottom diagram). As mentioned before, the goal here (right or wrong) was to get the output u-joint angle and pinion u-joint angle close. You can also see that the pinion is about 2° below the second shaft slope. I assume that angle reduces under load as the pinion deflects upward slightly. Perhaps its more than 2° (pinion points above slope) and that's why I get the noise under acceleration? Starting to think the 3° shims were overkill or maybe didn't need them at all. Just drop CB until pinion pointed at it. Idk

 

I would try to get the working angle of the pinion u joint less than 2 degrees and closer to 0.5 down.
The pinion will rotate up during acceleration and under load but will most likely flated back out at highway speed.
All of the angles from the DC joint to the transmission output should be fine.

 

Ok, it looks like if I keep the 0.5" spacer but just flip my CB back around it should get me there. I will try that next, thank you.

 

Flipped the CB last night and re-measured. Was damn close to what the model calculated. From left to right above I measured: 3.3°, 8.3° & 7.9° yielding a rear pinion u-joint angle of 0.4°below the slope of the shaft.
Unfortunately the shake over 65 mph is still there, as well as the hum (bad bearing like) noise. The noise may be a tad better.

Starting to wonder if this aftermarket shaft is defective. I raised the rear axle on jack stands and watched the DS rotate at idle. There seems to be a wobble in the second shaft. Initially, I thought maybe this was due to incorrect angles, but it was still there after the latest adjustment. I took a video dragging a credit card along the side of the shaft and you can watch it deflect as it rotates. Intermediate shaft appears to spin true. Maybe that's why RockAuto had this specific drive shaft for half the price compared to anywhere else...

 

if you have 4x4, remove rear DS and go for a spin in 4wd
if no vibes, then its the shaft or angles

tube of shaft should not wobble when spinning

 

Thanks Knotty, I may do that just for a sanity check. Below is a link to a quick video showing the DS wobbling. It's pretty obvious if you look at its shadow in the background.
https://drive.google.com/file/d/18R9aDXhNr6pdBiaLe6A2C2UC5aqxRDeb/view?usp=sharing