Yep, the SHO bracket is cast iron. It's less than 1/4" thick where it bolts to the knuckle and about 1/2" thick where the caliper attaches. I used a high grade(expensive) 1/4" plate steel to fab my new brackets. I would have used thicker steel but then the bracket mounting bolts would not clear the base of the hub. The smaller piece welded to the top is 3/16". I was thinking the same thing you probably are. The 1/4" steel plate wont be as strong as the OEM cast bracket. But if you look at the rear pic of the assembly, you can see that the distance from the knuckle to the large holes that the caliper bolts to is less than 2". So you would need a tremendous amout of force to bend the new plate over that small a distance. Also, if you look at the physics involved here you can see that the force exerted on the bracket during braking will be acting in a plane which is parallel to the plane of the bracket. So the force will be trying to turn the bracket around it's axis(the spindle). Since the bracket is nearly 6" across, it seems impossible that it will bend in any way. The only forces that "might" bend the bracket are those that work perpendicular to the plane of the bracket. But since the SHO caliper is a full floating system, perpendicular forces are almost zero. The only way there would be perpendicular force on the bracket is if I had a warped rotor or the caliper sliding pins siezed up. I will ensure neither of those things happen on my car.
One more thing to consider is that the rear brakes only do 15-20% of the braking. So the components won't see anything near the stress that the front brakes will. I would not even consider doing this type of thing for the front brakes.
Hopefully I can drag my @$$ out of bed before noon(it's 3 am as I'm typing this!) and get the hubs and rotors to the machinist. I need him to:
-machine the hubs about 1/8" so they will fit inside the SHO rotor hat.
-enlarge the centre bore on the rotors so they will fit on the topaz hub
-drill the 4X4.25" bolt pattern into the rotors
-resurface the rotors
-drill a 1.75" hole in the custom caliper bracket where it will fit over the topaz spindle. I did the first one myself but it was alot of work since I dont have a drill bit that big. The bolt holes I can do myself.
The first rotor that I modified myself is basically ruined(out of balance.) So I though I would have to buy a new one. But as luck would have it, 89 SHO's used the same rotors on all 4 wheels. So I still have 3 to work with. Hopefully atleast 2 are not warped beyond repair. Once the machining is done and I finish the second caliper bracket I should be able to bolt everything back into the Topaz and get some more pics. Then all that's left to do is hook up the brake lines and e-brake cables. Then on to the front brake upgrade!! :)
quote-"#3, what is the reason for the two outside lugs (undrilled) being left on? " I'm assume you are talking about the tabs that stick out of the new bracket? Those are the mounting tabs for the dust shield. I left them undrilled because I'm not sure if I will install the shield. I think it will look better without them.
On a side note, I place an order with www.shonutperformance.com
for a new clutch, front and rear crank seals and oil pan seals. I was going to wait until I was ready to order a Quaife TBD
but I might as well get these parts now so I can atleast get the engine buttoned up. SHOnut also informed me that my SHOshop y-pipe(from the group buy)is slated for delivery in late august. I knew it would take a few weeks since over 40 people signed up for that group buy! I have also heard that there can be a long wait(months) for a quaife TBD
since Quaife wont produce them until they have 25 orders. Oh well, that'll give me time to go nuts on the rest of the car. i.e-front brakes, subframe connectors, strut tower brace, etc.