Lift related axle wrap / driveline vibration issue...

I started with a 3/1 lift using 1" blocks in the rear.
Truck drove fine but had very minor low speed accel vibration. Barely noticeable, but there.

Shortly afterwards, I added 2" shackles (for 3" total) along with a carrier bearing drop kit for a 2-4" lift.

The vibration went away completely under light accel and normal driving... but now has a pretty noticeable vibration under hard acceleration at low speeds. (5-20mph)
Rolling down the highway at speed or easy normal driving, it's smooth as silk.

I am assuming this is pinion angle related when the leaf springs wrap/twist under low speed heavy load.

I understand how the rear geometry works... and how the longer rear shackles rotate the pinion up, while a block kit better maintains it parallel to the ground.

My thoughts are this...

Either:

A: Install helper springs or add-a-leaf pack to firm-up the rear springs and prevent axle wrap...

B: Install a shorter spacer in the carrier bearing drop kit.


Looking for advice, opinions or similar experiences.

TIA

 

Axle wrap reveals itself most obviously as a bump type feeling when coming to a complete stop (the axle rotating and pushing against the driveshaft). It's not a vibration per say. Vibration in the driveshaft can absolutely be related to a drop angle and present under hard load.

Experts like @Coachbuilder1 know this much better than I, but I would suggest that your combo of a 2" shackle and block would do best with a smaller carrier drop spacer.

 

I just checked my orders... and it appears I used the 3"-5" carrier drop kit with the taller (1.25") spacers... (since total lift was 3")

For the sake of experimentation... I will order the 0"-2" drop kit (.750" spacers) and try that instead.

Here's what I currently have:

 

I got a magnetic angle gauge and loaded the rear end and unloaded it and stacked washers on the drive shaft carrier besring until it was off a couple of washers( perfect can cause binding). Then ordered a spacer the size of the washers. It ended up being 1.5" for 5" rear lift on my taco. Angled block shims were too extreme. . I also took the leaf pack apart and added a chopped off leaf from another pack about a foot long and added it to stop the spring pack from flexing as much right after the ubolts when it has a heavy load. I was doing a u bolt flipkit with Timberen bump stops at the time because they needed to be taller.

 

I just removed the 1.250" spacers and put in the .750" spacers.
Its better... but still rumbles under hard 0-20mph acceleration.
Im 99% certain this is pinion angle related and only when the springs deform under hard launch.
It needs the pinion turned down or it needs more support on the forward half of the leaf pack.

What we use to do 30 years ago for drag racing... was to pull the leaf pack apart and spin them around so all the longer halves were toward the front of the car. It helped immensely at the dragstrip.

Maybe my 1" block and +2" shackle is a bad combo.
Maybe a 2" block and 1" shackle will work better... or just a 2" block and stock shackle.