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Discussion Starter · #1 ·
11 sierra 2wd sle. The steering wheel and body shake around 70 mph and goes away past 80. Smooth as could be any other speed. Not sure what a driveline issue would feel like but I'm thinking shims might need to be my next stop. Mcgaughy adjustable kit.
 

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My guess would be the drive shaft. I'm not savvy with drive shafts, so hopefully someone else will chime in.
 

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also, check to see if theres any part of the u-joints that are bound, drop the driveshaft and cycle the joints and see if theres a catch anywhere
 

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i have the same issue and same kit. will be doing shims when the weather gets better
 

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I have vibration when accelerating from any speed. It stops when I level off at whatever speed I'm at.
I guess I need to figure how to check the driveshaft angle and what it needs to be. I already have the transmission spacer, that came with the kit.
Mcgaughey's adjustable on mine.

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also, check to see if theres any part of the u-joints that are bound, drop the driveshaft and cycle the joints and see if theres a catch anywhere
I would do this ^^^^^^^ before anything else. Easy to do and doesn't cost a penny.
 

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I don't disagree, however it didn't start until I dropped the truck. I would assume that the joints would have behaved similarly before then. Would it not?

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I don't disagree, however it didn't start until I dropped the truck. I would assume that the joints would have behaved similarly before then. Would it not?.....
The u-joints may have worn in a pattern according to the driveline angle that originally existed, and now that you are out of that pattern, you're getting a vibration. I only say this because I have replaced lots of u-joints in my career as service station owner and I've seen all kinds of interesting wear patterns in them.

Of course, if you change driveline angles then there is a big chance of inducing driveline vibration.... BUT ..... it would really suck for you to go through the trial and error of adjusting driveline angles - without correcting the vibration - only to discover it was a bad u-joint all along.

You're gonna be under there anyway, so why not check the most basic and obvious thing first? In the automotive business, one must always consider "Occam's Razor", which is the problem-solving principle that essentially states that simpler solutions are more likely to be correct than complex ones.

Good luck! I'm sure you'll fix it one way or another. ;)
 

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You are absolutely correct, it's not like I don't spend time under the truck. I just finished installing helper bags and a compressor, so I will give that a whirl and see what happens.
And I thank you for taking the time to share your thoughts on this.

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Here is a short video that demonstrates what happens when the U joints, drive and driven angles are not the same. Also shows what happens if the U joints are not in phase....
Nice little video about drive line angles. I wish he would have amplified his explanation (and demo) of phasing. I've always assumed out-of-phase simply meant that the front and rear u-joints were not lined up????? But I am guessing there's more to it than that. I'm gonna Google it up.
 

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Nice little video about drive line angles. I wish he would have amplified his explanation (and demo) of phasing. I've always assumed out-of-phase simply meant that the front and rear u-joints were not lined up????? But I am guessing there's more to it than that. I'm gonna Google it up.
No more to phasing, you are correct. It just means the two "U"joints are not lined up. Since most light duty trucks and cars have the slip splines on the trans output shaft they cannot be installed out of phase. Larger trucks with multiple piece drive shafts can be installed out of phase.
 

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No more to phasing, you are correct. It just means the two "U"joints are not lined up. Since most light duty trucks and cars have the slip splines on the trans output shaft they cannot be installed out of phase. Larger trucks with multiple piece drive shafts can be installed out of phase.
That video inspired me to install two new u-joints in my rear driveshaft. I am getting vibration (felt in seat, NOT steering) at ~75mph. I suspected u-joints, but the old ones were not too bad. I got out my electronic level and measured the driveline angle between tranny and diff, which seems to have 2* variation... I am wondering if that is too much?? Anyone know what the tolerances are on driveline angles??
 

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I haven't checked my angles yet, but I did notice today, that my whole rear end is 3/4" to one side. I'm going to check my driveshaft angle, but am curious if the side angle may cause this also.

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That video inspired me to install two new u-joints in my rear driveshaft. I am getting vibration (felt in seat, NOT steering) at ~75mph. I suspected u-joints, but the old ones were not too bad. I got out my electronic level and measured the driveline angle between tranny and diff, which seems to have 2* variation... I am wondering if that is too much?? Anyone know what the tolerances are on driveline angles??
Another possibility is you lost a balance weight. They are spot welded on and can rust and fall off. Sometimes you can still see where they were. Also if the slip splines are worn from lots of torque or the rear trans bushing is worn, and you can wiggle the yoke up and down this will also give you a vibration.
 

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Another possibility is you lost a balance weight. They are spot welded on and can rust and fall off. Sometimes you can still see where they were. Also if the slip splines are worn from lots of torque or the rear trans bushing is worn, and you can wiggle the yoke up and down this will also give you a vibration.
Thanks... I did see the balance weight was still in place and the driveshaft did not have any dents in it. The slip spines are snug, truck only has 101k miles and has been well maintained.

The vibration is quite noticeable and it's definitely in the rear. Very smooth up until ~75mph, then it kicks in. It reminded me of that rotational speed variation in the video, and that's why I'm a little curious if a 2 degree difference in driveline angle would cause that effect.

I think I'll try a new tranny mount first. I was indeed thinking about the rear transmission mount and was looking at them yesterday. I would like to buy a true GM part rather than some Chinese knockoff. Any idea where I can get OEM tranny mount? Thanks

OP - not trying to hijack your thread. Just trying to help you out, as well as figure out my own (similar to yours) vibration issue. ;)
 

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Discussion Starter · #19 ·
Thanks... I did see the balance weight was still in place and the driveshaft did not have any dents in it. The slip spines are snug, truck only has 101k miles and has been well maintained.

The vibration is quite noticeable and it's definitely in the rear. Very smooth up until ~75mph, then it kicks in. It reminded me of that rotational speed variation in the video, and that's why I'm a little curious if a 2 degree difference in driveline angle would cause that effect.

I think I'll try a new tranny mount first. I was indeed thinking about the rear transmission mount and was looking at them yesterday. I would like to buy a true GM part rather than some Chinese knockoff. Any idea where I can get OEM tranny mount? Thanks

OP - not trying to hijack your thread. Just trying to help you out, as well as figure out my own (similar to yours) vibration issue. ;)
All good man. Putting a belltech trans spacer on tomorrow. Will report back. Gmpartsdirect.com for oem parts. Google for a part number
 

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Thanks... I did see the balance weight was still in place and the driveshaft did not have any dents in it. The slip spines are snug, truck only has 101k miles and has been well maintained.

The vibration is quite noticeable and it's definitely in the rear. Very smooth up until ~75mph, then it kicks in. It reminded me of that rotational speed variation in the video, and that's why I'm a little curious if a 2 degree difference in driveline angle would cause that effect.

I think I'll try a new tranny mount first. I was indeed thinking about the rear transmission mount and was looking at them yesterday. I would like to buy a true GM part rather than some Chinese knockoff. Any idea where I can get OEM tranny mount? Thanks

OP - not trying to hijack your thread. Just trying to help you out, as well as figure out my own (similar to yours) vibration issue. ;)
Did you check wheel weights?
 
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