16 year old Yard Machine - Differential Replacement?

Mower Model = 13AF675G062
Purchased April 2002
Problem = Suddenly started jerking. (Imagine the throttle moved between fast and slow.) Then it started popping when mowing, getting worse up an incline and when turning. The more it was used the worse it got. I only used it 1 cutting after the popping started. This occurs in forward and reverse.

So my first thought was a worn clutch or selector arm. When I took the trans apart the clutch and gears were in ok shape, nothing immediately noticeably wrong. But when I lifted the axle /differential out what looks like pieces to a keeper or some type of spacer fell off. (I have attached pictures.)



These pieces fell off the right side of the differential housing. Is this an indicator of a bad differential? Should I look at something else?

Usually the older yard-machines had a Peerless "Transaxle" in them, see if you have an ID label somewhere on the lower/upper housing, post that if you find it, meantime see if any of this is of help......



http://www.barrettsmallengine.com/manual/tecumsehpeerlessmanual.pdf

Thanks, the trans housing is stamped MTD 719-0313B, a sticker has 618-0163B. I was able to use the site you recommended to find a more detailed parts diagram.

I still could't identify where the broken pieces came from. My best guess is it came from inside the differential housing. I am not having any luck finding a break down of just the differential.