TMK those are small bearing 9" backing plates and should be 10" shoes, I don't think they made 11" for the small bearing but not sure. I think you measure the shoe from end to end (top to bottom in your pic) to get the 10". The 'D' shape of the indentation is what tells me they're small 9" ends. Here's a pic of the large and small next to each other, see how the small is 'D' shaped:
You'd also be able to tell if you took the axle out as the big 9" bearing has a cone shaped bearing on it where the small doesn't:
According to this site, where I got the pics from:
http://kevinstang.com/Ninecase.htm
The 11" came in 11"X2 1/4" most commonly on trucks and full size cars, the 10" came in 10X2", 2 1/4" and 2 1/2". I think the 11" only came on big blocks and the drums had 'fins' on the outside like front drums do where the 10" were smooth.
I installed a small bearing 9" in my '67 and it had 10" backing plates with 2 1/4" shoes TMR. I needed new drums for it anyway so I got 2 1/2" shoes. As I recall the Raybestos part # for the 2 1/4" and 2 1/2" shoe drums was the same so I guess the smaller shoes just didn't touch the entire width of the surface, saved them from making 2 different drums.
I figured the differnce between 11 X 2 1/4" and 10 X 2 1/2" would be negligable and not worth the $$ to find 11" backing plates, springs and all the other parts that are probably different. The shoes would be 1" taller but 1/4" thinner all the way around. I don't remember my math well but if you multiply those measurements they come out w/in 1/4 sq. inch of each other I believe, am I doing that right? 11X2.25=24.75sq.in. and 10X2.5=25sq.in. so the smaller wider actually cover more area. I'm guessing the larger drum would have more cooling surface though?
Jon
