[57taskforce]

Next I’ll get into specifics on the hubs and rotors. In order to properly center the rotor to the hub, the late model hubs have a boss machined into them that is the same diameter as the inside of the center of the rotor. I had the back side of the ‘89 drum brake hubs turned down .02 deep with an outside diameter that matches the center of the rotor.. At this point I had a friend who owns a big industrial machine shop we use at work make me up some backing plate mount flanges. These flanges were cut on a water jet and finished on a CNC mill. They are cut from 3/4” plate and have a boss built into the outside of them to center the backing plate/caliper mount. He used the backing plate/caliper mounts as a guide and had the centers cut for the slightly smaller ‘89 14 bolt axle tubes.(the factory disk axles have slightly larger Dana 70 spec axle tubes) They fit over the tubes snug, but not a press fit, to keep them centered on the tubes. As you’ll see in the last picture below, the drum brake flange is a square and the disk brake flange is more of a trapezoid. The trapezoid being considerably larger than the square in this case. In short the drum brake flanges will not work to mount the disk brake backing plate. Here’s some pictures of the hubs, backing plates and flanges.

Picture one and two shows the boss machined into the hub to center it to the rotor. In picture 1 the knife blade is resting on the new boss. The boss that is about 1/4” above the tip of the knife is the original used to center the brake drum. Notice the rotor has a bigger center diameter than the drum did.

The second picture shows the rotor resting and centered on the now machined hub. The lug studs will press into the rotor and hub from this side to pin the rotor to the hub.

The third and fourth pictures show the newly machined backing plate flange, and the backing plate/caliper mount. Notice how the flange has the boss machined into it to center into the recess that is factory machined into the center of the backing plate.