Re: What's up with my brakes????
Post by barrman on May 19, 2006, 12:35pm

The stock brake drums are too big to mount on a normal automotive sized brake lathe. Therefore, you need to mount the hub to the lathe first. I use wedge or actually rounded ball shaped collets that fit inside the bearing outer race to mount the hub to the lathe. So, the bearing race placement is what centers the hub. I only tested one hub, but it had less runout than the tolerance on the brake lathe shaft. That means that any runout I had on the hub could have been the hub or the lathe itself. I think it was less than .003" if I remember right.

Now, here is the weird part. When you add a drum, the runout on the drum will change depending on which of the three possible ways you can bolt the drum to the hub with the three set screws. I tried all three locations and marked the best. that is when I went ahead and cut the drums to make them as round as possible. I cleaned all the dirt and paint off the hub mounting surface and the drum mount surface. I don't know if our drums are just "Lowest bidder" huge tolerance parts or the center of the hubs are that off center from the factory and the extra size of the drum makes the small runout at about 4" really evident at 13".