Need help with drive shaft angles

I am in the process of figuring out my driveline angles to help with a small vibration I’m getting during medium acceleration at around 8mph from stop.

These are my current angles

 

What is your baseline? The ground? The flat spot on the transfer case? The pumpkin on the rear?

 

Do you mean what am I zeroed on?

 

Yeah

 

2 or 3 degree shims will probably fix that. I put 3 on and it's smooth as butter.

 

Ideally, you should zero on the flat spot of the transfer case then put the level on the small flange on the pinion coming out of the transfer case connecting to the driveshaft (where the bolts are, there’s not much room). Get that measurement. Then you zero the level on that same flange and go back to the pinion on the differential and see how close to 0 the measurement is. The closer to 0 the better, you would want it to be within 1°. Then where the carrier bearing is, you want the difference between the two driveshafts to be close to 1°, if it’s 0° there’s a good chance you can increase wear on the carrier and cause binding in the pinions which would cause additional vibrations.

That’s what I’ve learned from the various threads and conversations I’ve had about this when I was adjusting the angles. Haven’t had a problem yet

 

The formula for working angles is:
A+B+C=0
Downward working angles are positive, and upward working angles are negative.

According to your numbers, you have:
5.7+3.2+(-5.8)=3.1
Or a 3 degree shim, thicker to the front.
You need to increase the C working angle for it to balance.

All that said, I don't think you measured correctly or your carrier bearing has dropped. 5.7 for the "A" working angle is excessive.

 

I’m on a 7” lift so I have a good size spacer at the carrier bearing right now. Possibly over an inch.

Don’t I want the t case working angle to be close to 0 ideally? And then I work backwards from there? I’ve also read that as long as my t case working angle and pinion angle at the diff are similar, I just need to get the two drive shafts to be within 1 degree and it should work

 

Ahh...
You might want to consider a new driveshaft and/or a ladder bars
You're driveshaft is more than likely not long enough and the rear spacer lift is magnifying axle wrap.
Either, a one-piece with 2 u-joints or a two-piece with 2 u-joints and 1 double cardan joint.

 

I’m actually only on a 2.5” spacer paired with OME HD leaf springs, however, I think you’re right. I wasn’t sure if the drive shaft needed to be longer. I assumed the slip yoke had a decent amount of play, but maybe not. I’m looking into a single piece with a double cardan currently as well.

 

A one piece double cardan will have 1 double cardan joint at the t.case and 1 u-joint at the pinion...
The u-joint will need a 0 degree working angle. This requires angling the pinion up signicantly.
There is a risk of starving pinion bearings. Some 'overfill' to compensate.

 

I see what you’re saying. I think my first option is going to be taking it back to the shop that installed my lift and see if they can get the working angles to what they need to be. I’m mostly feeling vibes on medium to hard acceleration from dead stop, so I think a traction bar would be my next step after playing with the angles.

 

With the angles, you can do one of two things with the stock shaft. 3 degree shim(thick side forward), as I said before. Or, keep lowering the carrier bearing and playing with the pinion angle until you can get this for the working angles:
A=C
B=0


The former will have working angles of:
A=5.7
B=3.2
C=-8.8

The latter will have working angles of:
A=5.2
B=0
C=-5.2

U-joint life expactancy is based on a 3 degree premise; and as expected, diminishes the higher it goes.

 

The latter method may require dropping and shimming of the carrier bearing.

 

So the working angle up at the transfer case doesn’t have to be zero?

 

With the stock shaft, there's 4 different ways to balance the working angles.

A+B+C=0

A=C
B=0

A=0
B=C

A=B
C=0

 

Now I see it. So A - 5.7 B - 3.2 giving me positive 8.9. My pinion working angle is negative working 5.9 so a 3* shim fat side forward would put me at negative 8.8 and bringing me to 0 overall.

meaning that in this case we don’t care about the carrier working angle being zero or not?

 

You got it...

Could be a 3 degree; maybe a 4 degree.
As you lower the pinion to get more negative working angle at C(thick side forward shim), B will also increase.

 

Here’s something I didn’t think about, but my 2.5” blocks have a taper on them. Is it possible that a non tapered 2.5” block would yield the same results as throwing in a fat side forward shim now?

 

Depends...
How many degrees taper are on the block and what direction are they installed?