BRAKE DRUM QUESTION......

I've noticed a difference in various model rearv brake drum cover plates and can't seem to find an answer in the service manuals or parts books, so........thought I'd ask and really test someone's expertise and knowledge!

On some of the XJ series rear brake COVER PLATE, around the axle hole there are three "slots" or grooves cut into the axle hole, and such slots extend all the way through that hole, as though some type of alignment pins or woodruff keys (etc.) would be located in these slots. You can see a good image of these slots on this eBay auction:

http://cgi.ebay.com/ebaymotors/1982-Yam ... p1638.m118


Whereas other models do NOT have these slots, as on this item:

http://cgi.ebay.com/ebaymotors/1983-Yam ... 0145145161

I realize that these two auctions are for two different model bikes, but in reality, the 550 Maxim backing plate is the same as the 650 all models backing plate, with the only unique feature of the Turbo model plate is that it is black rather than natural in finish.

Anyone know the answer to this mystery?

 

You know - with all the times I've had the back wheel off, I've never noticed which one I've got for sure -- but pretty sure mine does not have the grooves.

The only think I could think of to explain these would be some form of simple reservoir for axle grease? Don't know why as there's no rotation at that point, but maybe. Can't imagine expansion slots would need to be so large...