Large Rear Drums ?

I was wondering how to determine the size of rear drums. Where are they measured. Across the backing plate, across the drum, across the shoes? I bought a 8.5" from a Olds Vista Cruiser, and the drums appear large. Will these bolt onto the end of a A-body 10 bolt 8.5"? I've been reading about these at
http://www.buickperformance.com/85rear.htm does anyone have any ideas in addition to these? Thanks

 

The A body has a 5/4.75 bolt circle, that wagon has 5/5.

PS: Still waiting for that photo, Rich :TU:

 

The Olds is an A BODY wagon

 

Yes,

But the wagons had bigger brakes.

 

The Vista's had larger rear brakes and they are measured at the shoes. As long as you use the drums and correct size shoes, all is well. That Vista should also have 3.08-3.42 gears.

 

I thought the wagons had wider brakes- not necessarily bigger diameter.

For some reason I'm thinking 1/2 inch wider.

-Bob Cunningham

 

I believe they are wider since they use the same backing plates as other A-bodies.

 

Many pre '73 A-body wagon's backing plates were stamped differently than normal '64-72 BOP A-body backing plates. When mounted on the hsg, the backsides of the backing plates set closer to center of rearend. This design was all in order to run wider brake shoe. Have been stocking up on such backing plates, not because they take wider shoe, but due to having larger bearing hole. Many early Buick & Olds A-body wagons had same backing plates, so they can be found.

Rich, just keep these A-body SW backing plates to mate with your new housing. Even if you rebuild the brakes on them, you can run std width drums, such as the alum '78+ drums. This is std practice on higher hp 8.5's I build.
:3gears:
Roger

 

The one I bought...

This one I have is actually out of a newer(Mid eighties) VC wgn. I bought it to see how the inner workings worked before I tried laying under one at the 'recycler' trying to remove the pieces I need. The brake drums are defenately about an inch larger in diameter. The axle has about two inches of additional width compared to my GS 10 bolt that is under the car. This is a '70 model 8.2" judging by the rear cover, that is under my car. I imagine it is the original but I've never checked the numbers. This ring gear that I got is the 15 41 so I guess it is the 2.73. I will keep searching, and learning. Oh, and it is 5 on 5 bolt pattern, but I think I can get the drum redrilled to use on 5 on 4.75 axles. Thanks to all who replied.