Shake/Vibration when Towing

[Caman96]

NITRO-GIRTH!

"Up" and "Down" refer to the angle of an item as installed on the vehicle, from front to rear. Higher in front is a downward slope, higher in the rear is an upward slope.

Measure your driveshaft angles WITH THE LOAD ATTACHED. I would expect the axle pinion to be a degree or three "down" compared to the transmisson/transfer case, because it'll rise under torque, and under torque the pinion angle should be the same or nearly the same as the transfer-case angle.

Here's a Spicer calculator for U-joint angles. Using your figures of 11, 7, and 5 degrees, all "down", your front U-joint is operating at a 4 degree angle, and the rear U-joint is operating at 2 degrees. Yeah, I bet it shakes. But again, the angles when loaded are going to be more important.

Spicer Driveline Operating Angle Calculator

Measure the angles of each component in your drivetrain, then use the Spicer Driveline Operating Angle Calculator to find the operating angle of each u-joint in your drivetrain.

spicerparts.com

and a video showing how to measure and calculate angles:

Measuring Driveline Operating Angles | Spicer Parts

Driveline set-up, diagnosis, and repair is an easy process, but it is often misunderstood. This video offers a quick tutorial that can makes measuring driveline angles a snap.

spicerparts.com

Thanks @Schurkey, will check all that out. 2 questions, I was also thinking about measuring under load, but what about when not towing? Find a happy medium?
Also, what about that reduced driveshaft thing I mentioned above?

 

[Caman96]

Ok, with numbers I got today entered in that, I get this.

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Anything above 3 is no good. So by shimming axle and increasing “Driven Member” to 9°, I’m guessing the middle “Driveshaft” number would also increase(is this right), if so, I’d get this.

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[Supercharged111]

You're still using your phone for the angles? I kinda want to nerd out and check mine too. I don't have any vibrations or anything, but I have deviated from stock.

 

[Caman96]

You're still using your phone for the angles? I kinda want to nerd out and check mine too. I don't have any vibrations or anything, but I have deviated from stock.

Most of these online calculators including the Spicer above say phone is fine. I even checked phone again to my Stabilia level yesterday and it’s dead on. Just make sure to remove phone case. Let me know what numbers you come up with. As mentioned, I had felt an occasional vibration and always thought tire balance. I’m guessing while towing it get amplified.

 

[Hipster]

Never heard that driveshafts that reduce in diameter would be cause for an issue like this. If you had 700 ft lbs of big block you might want to go with a straight shaft. I think they're trying to sell you something just to sell something.

 

[Supercharged111]

Never heard that driveshafts that reduce in diameter would be cause for an issue like this. If you had 700 ft lbs of big block you might want to go with a straight shaft. I think they're trying to sell you something just to sell something.

My guess is they were getting toward it being weaker and lowering the critical driveline speed, but those small diameter sections are so short they don't do squat for that.

 

[Caman96]

Never heard that driveshafts that reduce in diameter would be cause for an issue like this. If you had 700 ft lbs of big block you might want to go with a straight shaft. I think they're trying to sell you something just to sell something.

My guess is they were getting toward it being weaker and lowering the critical driveline speed, but those small diameter sections are so short they don't do squat for that.

Yeah, with that driveshaft and towing 2200 lbs., GM couldn’t have been off that much, considering they say 6K towing capacity.

 

[Hipster]

My guess is they were getting toward it being weaker and lowering the critical driveline speed, but those small diameter sections are so short they don't do squat for that.

I get their reasoning behind suggesting it. It's kind of the go to answer when dealing with a driveline shop, but were not talking about crossing stripes in a high hp application @7k rpm. The stock shaft that's just been rebuilt and balanced should suffice.

 

[Hipster]

Maybe I'm just old school but not really not digging on the calculators.I like paper for the visuals. Imho the angle of the driveshaft is not all that important here unless it spinning in the same plane as everything else causing the harmonics or operating at angles it's binding. You can do a 4 inch kit on one of these without needing cv driveshafts and this truck is near stock. It might take a little experimentation to figure out the happy medium between loaded and unloaded. Really need loaded and unloaded numbers for comparison purposes here. How out of whack it is under load compared to the static measurements will determine which way to go and how much. Might end up at the outer limits of what the books call good loaded and unloaded to get to a place where the truck is happy both ways. It's kind of being overthought at this point.

 

[Caman96]

Ok, just got off the phone with Tom Wood’s Custom Driveshaft, I think their in Idaho. Gave him my numbers and right away he knew something was wrong and the transfer output number was it. He said literally everything stock is about 5°.

My 11° number was wrong, way wrong, found a more accurate place to read. Mine is 5°.
That being said, this guy went through at least 30 minutes of taking information on truck, did all kinds of calculations and said driveshaft is perfect and Balance Shop saying I needed a new one was complete BS.
So in the end, he believed the wheel shake was it either needing a alignment tweak or a steering stabilizer. I’d say this is good news considering. Pic below showing updated correct numbers.

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He said 0° is no good and need to reduce pinion 2° to get to 5°. But, even correcting this, his opinion was that wasn’t cause of wheel shake when towing.