63 12 Bolt Rear Bearings and Shims

[rbruno68]

I took my rear apart to have it cleaned and a new posi added and when I pulled the bearings out, I had a shim come with it. I have read at least a half dozen threads or more on the forum that talks about the shim. The picture below has the shim, the old bearing race and new bearing. I can't say that the threads came to any conclusion on what the shim is for and if it is needed. I took some measurements and the Shim measures .063 thick. The new bearing is .816 thick and the old race is .825 thick. So if I use the shim, it won't push the bearing out any further then the original because the new bearing is slightly thinner. My old race diameter is 2.528 and the new one is 2.535, so slightly bigger. With as easy as the race came out, I think a little more crush wouldn't hurt. I bought new Moser axles because I went with posi and needed the 30 spline axle. I don't have an issue with a worn axle where the bearing or seal will ride. The seal looks different then the original, but it has crush in the axle tube, so I don't think that is an issue. But, wondering if I need that shim and what is the purpose?

[Accelo]

.007 thousand is not a little more, it's a bunch for something a nominal 2.5" in diameter.
It will require tons of force to install this and will likely reduce the internal diameter so much that the axle will not install with the necessary diametric clearances.
" With as easy as the race came out, I think a little more crush wouldn't hurt", you need to measure the bore to get the exact interference fit.
Typically, it would be in the order of .0005 per inch in diameter. I would expect to see .0015 to .002 interference fit in most applications, with this diameter.
I suggest you look for a better/different bearing.
I have experienced this issue before. I'm glad you identified the size issue before the installation. In my case, I did not identify the fitment issue, the first time I did this. I believe they are just substituting another "close to size" bearing.
There is no way a bearing manufacturer would be this far off in sizing.

Since this is a straight roller bearing, no shim is necessary. Seems more like a splash shield than anything.