My Tahoe has a very short drive shaft due to awd and it being a very short wheel base. the pinion has this huge round thing on it (about 6-8" and an inch or so thick) that looks like a crank balancer what is it? is it to help vibes on such a short shaft?

 

yap, helps with vibrations.

 

so if i get a new drive shaft do i need to keep this part?