Is my final drive going out?

[Yamaha32088]

I suspect my final drive to be going out. I started another topic asking about swaps but I wanted to start this one to see everyone’s thoughts about the noise I am hearing. It is a clunking/knocking and sometimes grinding noise coming from the rear.

[Yamaha32088]

In one of the videos where you can see the brake caliper that grinding noise is clearly the brake pads but sometimes there is a much worse grinding noise coming from the rear.

[saddlebum]

Rear end grinding noises can come be from several causes. 

1. Brakes worn to the metal can make one heck of a grinding noise
2. failing u-joints in the drive tube 
3. failing bearings anywhere in the drive line 
4. Middle drive gear
5. cam drive assembly in the middle drive gear section

Try putting the bike on the center stand and while someone is manually rotating the the rear wheel try listening for the source. Keeping in mind that driveline noises can telegraph along the driveline make it sound like the source is coming from a different location than it actually is.

[Patch]

Coming back from a long trip some years ago my 91 began humming at speed. Then I noticed when parking the bike that th rollback was excessive. I pulled the final drive apart and found the pic below. I'll say this, it would be unwise to ride until you go thru it, NO shortcuts.