Background:

A few weeks ago i noticed a rather large thumping/thud coming from the front end when I went over a bump. I thought I had broke a shock or something. Did not do to much about it other than taking a very quick look. I backed the blazer out one day to clean the crud off my driveway and found this. Once i found it..no more thump..

Description: 1/2 of about a 6 or 7 inch in diameter piece of cast iron that weighs about 6 pounds.

My question is: what the hell would it be. Counter weight, vibration dampener?

Not to concerned about it the truck has never run better than it is right now

Here are some pictures of it...

Thanks in advance

 

Sure doesn't look like something I have ever seen on any vehicle, let alone a Blazer. Are you sure it came off of yours?