Rear Disk Brakes - 1954 Pontiac
One of the nice things about the Toronado style of rear disk brakes, are the emergency brakes. They are not minature drum brakes but work off of the disk caliper. They are very simple and effective. Another nice thing is that the brakes are 10.5" diameter, a little less than the Camaro's but still pretty hefty for a street machine. Finally, the complete rotor/caliper package is very narrow, much more than a Camaro which means that there are less clearance problems. BTW, it's easier to disconnect the 4 bolts holding the rear hub to the rear suspension and take the complete hub/rotor assembly then to take the rear brakes apart.
Toronado's rear brake/hub assembly
You can use the Toronado's rear caliber mounting bracket on your 10 bolt Chev rear-end (pix and machining drawings to follow). It takes a bit of machining to do. First, a 0.160" spacer is required between the hub and rotor to place the rotor in the correct position. I made mine out of aluminum. It's basically a 5.75" diameter disk with a center hole to go over the hub and 5 wheel stud holes.
Toronado caliper mount (looking from tire side). Note the evenly spaced mounting holes.
Toronado caliper mount (looking from diff out)
The rear axle outside diameter has to be turned down to 5.75" (just like the Nova's drum hubs) so that the rotors fit over it. This requires removing the axles. A slug has to be made to extend the axle hub because the original drum brake is only 0.125" thick and the combination of the spacer (0.160") and rotor (0.300") is 0.460". There is less than 1/16" left to center the rims. I made mine out of steel, bored out the center of the hub and "pressed in" a 1/2" extension slug so that the rim would have something to center on.
Rear axle to be turned down and center bored out
This shows the slug in place in the axle and the rotor/caliper assembly already installed
Actually, I heated up the axle with a torch to expand it and put the slug in liquid nitrogen to contract it. The slug is 0.0025" larger than the axle bore and when both returned to room temperature, it will never come out. By the way, rule of thumb is 0.001" oversize for every 1" diameter for permanently pressed in fit like this.
The original wheel studs were now too short (1 1/2" long) so I replaced mine with Morosa 2 7/8" ones which I cut down to 2" in length. The next step is to modify the Toronado's caliper mounting bracket bolt and hub holes.
10 bolt axle flange showing lower holes closer together than top holes.
First the original bolt holes have to be welded closed - make sure that you have a certified welder do this! The brackets must be preheated, welded and then allowed to cool very slowly (3 or 4 hours!) to prevent the welds from hardening and the bracket from warping. If the welds cool too fast, the welds will harden and you will not be able to drill new mounting holes.
Because the axle flange has offset holes, drilling the caliper bracket to match is a pain in the butt to line up. I built a jig so that I can use one of the old drum brake backing plates as a guide. Still didn't line up great but it worked. Grade 8 bolts, lockwashers and nuts and the new disks and calipers were on the car! The center hole in the mounting bracket must be expanded to 2.900" from 2.800" to clear the axle flanges. One side required it but the other was fine, I did both anyways.