How to tell if a differential is going bad?
 

I searched and found nothing... gonna go look at a completely stock, 2001 Z28 M6 tomorrow, just has a drop and chrome C5 5-spokes, so I'll assume it has a 10-bolt. I was wondering what are some dead give aways that a diff a going bad, either from listening or looking at one. Of course I know to look at the engine and underneath the car, etc.

Thanks in advance

A stock 2001 has the Torsen (torque sensing) Zexel geared bias differential which means no clutches. The word I have heard is either they work or they are completely broken. Test drive the car, listen and feel if it makes noise or peculiar actions when accelerating, coasting or turning - if not, the differential is good under the present circumstances. Understand that the Zexel does not necessarily lay down two black patches like a good clutch type differential. The Zexel may only peel one tire but is on the extreme verge of spinning the other.

The key to any test is when all things are hot. In other words, a short test drive is not enough to know it all.

my disclaimer:
Be sure to wait for more replies than mine. I will be the first to admit that what I think I know is just that. Although I do own and operate a 2001 Z28 and have had some experience working on a 10 bolt, I am still just repeating from sources I have determined more knowledgeable than myself.

Noise is a give a way, you will hear whining while you drive, be it either acceleration, or on the decel. Stock should be dead quite, nothing more then tire noise.

But also mind you, if the rear gear has been changed, the quality of gear metal and installer exp will effect noise level too....