I recently did the 4L80E swap in my 2000 RCSB that is lowered 4-6. The trans works great but now I have what seems like driveshaft vibrations around 80mph and up. I used the prescision 447 bastard joint and a Jakes performance yoke. The drive shaft seemed to angle slightly upwards out of the trans tailshaft and be inline with the pinion. I installed some 4 degree wedges in the back and shimmed the trans up as high as possible. This helped a lot but it still seems to shake. I am extremely cautious about this as I do not want to throw a ujoint at high speeds. I guess my question is if I remove the flip kit and go 4" shackles and hangers will this change the driveshaft geometry any? Ive been wanting to lift it up a little anyways but this vibration is definitely priority.

 

I would first measure your angles for both and see what needs to be changed instead of sorta guessing at what shims you should install or remove.

I would maybe stick it back to how it was "stock" (without any shims) and measure first, that way you know which way to go.

 

I have a 04 RCSB lq4/4l80e with a 4.5/6.5 drop I have 6 degree shims installed and shimmed the trans up about 1/2 no vibrations but I do have a clunk when braking hard and going from drive to reverse and reverse to drive that I didnt have before when I was 2/4 .....

 

I guess what I am asking is by going back to having the axle under the leaf's with shackles and hangers going to alter the drive shaft angle at the trans.

 

Has anyone who has the 4l80E swap in a RCSB with a flip encountered these issues?

 

when you installed the flip did you install the plate that going on the bottom of the leafs in the right spot? its suppose to be installed to move the axle back 1 inch

Again i'm 4l80e swapped flip kit 6 degree shims and trans shimmed 1/2" higher no viborations but do have a clunk going in gears (u joints are good)