I am looking into replacing my leaf spring bushings. I am having a vibration around 80-90mph when i am at WOT. If i slowly cruise up to 80-90mph i don't have a vibration. I am thinking that under a heavy load the rear is rotating toooo much and causing the pinion angle to go toooooo positive thus creating a vibration. So i was looking into some Polyurethane bushings to help prevent it.. I will also be adding some caltracs or Assasian Bars in the near future. While i am replacing the bushings i plan on correcting the pinion angle as well.

Any thoughts?

 

Bushings can't hurt, but I would point the finger at pinion angle. What is it at now with the new drive shaft?

 

Currently
Driveshaft is 1-2* pointing down at the rear end.
Rearend is 4* pointing up


Goal
Driveshaft 1-2* pointing down at the rear end
Rearend 2* pointing down


I know it is off, and i am getting shims to fix that...

 

Id say if you can get ahold of a set of those assasin bars youll be fine. Plus they look really cool

 

corey this may help you:

Pinion angle

i had the same issues as you and i went by these guides or steps from rossler and all is well, well was lol i need to redo mine since my angle has changed since i messed with the 4 link recently!

 

That is awesome! I appreciate you posting that!

I was using this one.

http://www.wolferacecraft.com/pinionangle.aspx

 

Definately sounds like a pinion angle problem to me. Can't go wrong with Cal-Tracs! There's a couple of things I like about the Assasin bars that I like, and a couple things I don't like.

 

mine has always had a vib at 70-75 after the last 4L60E puked the output shaft and bent the center support cross member. i bent it back straight best i could and had to add shims to it to get it smooth at 70, but at 75 its still bad.
WOT it has a slight vib, but its always done that from when it was stock.

what angle finder are you using Corey?

 

Belltech makes a carrier bearing relocator kit which you can also use to adjust the pinion angle. It came with my 4" rear drop kit. I did not install it yet, but might have too. My shudders when taking off from a stop then a slight vibration at 15-25 mph. I currently have 2* shims with the fat end back.

 

My truck never vibrated until I did the 4l80 swap. My pinion angle just went retarded positive, like +7. Got it back to where I wanted it on the negative side and everything is smooth again