Need Advice on vibration issue

[shamb1s]

I have a 90 K5 I bought a few months ago. The truck was 100% stock when I bought it and ran great (and vibration free). I didn't waste any time adding a 4" lift. I got the complete kit from ORD: Tuff Country EZ-Ride up front, Shackle flip out back with stock springs. I also installed corrected steering arm, and sway bar disconnect/correct, and new 33" tires. Got the whole thing aligned and new tires mounted and balanced right away. Guess what? I have vibes. Mostly at the low end that go away around 50-60 MPH. I dropped the T-Case 1" and that didn't help. I know I need to do some drive line / pinion angle correction, I just need advice on which direction to go.

Option 1
Shim pinion angle back down to be parallel with T-Case output and lengthen the drive shaft. I only have about 2” of shaft in my slip yolk. I would also replace my u-joints at this point as well.

Option 2
NP241 SYE kit and custom CV drive shaft. Pinion angle is almost 0* in relation to the drive shaft at this moment. If this is the recommended option how do I identify what type of yolk my GM 10-bolt has so I can match it to the new T-Case fixed yoke.

I am also open to other options that I have not already thought of.

Thanks in advance for your help, this is a great community

 

[zombie1969]

Don't rule out a misfire thinking its a drive line vibe either. Have the tires rebalanced. Check the u joints. Check the drive shaft still has its balance weight tac welded in place and check if it got bent being lifted (at the shop) incorrectly. You can get washers and drop the tcase more 1/4 in at a time to see if it goes away. I got a 6in lift and a 2 1/4 in tcase drop with no vibes. 2 1/4 is a lot but it works and never had any problems. Also if you have overdrive when its vibrating drop it to drive and see if it stops. If it stops then its the drive line angle.

 

[hillbilly deluxe]

Might just be u-joint time.

The extra angle may have exposed a failing joint.

I used the ORD shackle flip and the 6" super shackles and had to shim my pinion down like 8 or 10 degrees to get it to look like factory angle. I have not lowered my t-case and have no vibration. Don't use the cast iron shims they are crap. Get milled steel ones. I think mine are from DIY4X or Sky manafacturing.

Check out this page from Tom woods driveshaft (if you haven't already):
http://www.4xshaft.com/

Love to see a pic, sounds like a nice rig!