I am going to fab some caliper brackets out of 5/16 aluminum plate to mount some Aerospace calipers on a 9" ford with 11.44" x 5/16" discs.
Is 6061-T6 adequate, or should I try to find some 7075-T651? Or something different? This is a street/strip car, but not a wintertime car, so corrosion resistance is not a big factor.
Thanks, Joel

Are you going to need to do any welding on them? If so I'd use 6061. It welds a lot better than 7075. Also 7075 is a bit harder to work with when machining, and I think it corrodes easier than 6061 as well.

No Welding needed. They will be 2 peices, bolted together. My son is going to waz them out on a CNC mill at school.

6061 T6 will work fine. the brackets on my diff
are made from it
EDIT
As to corrosion.. I painted them black(rustoleum
spray paint).. been on the race car over 15 years
now.. granted I'm not stopping 4000# but I stop
my junk from 151 mph and 99% of the time I dont
pull the chute.. just the brakes and on some of
the tracks its a short shut down area so I am on
the brakes pretty hard and with skinny fronts I
do about 85% of the braking with the rear tires

IMO, a 5/16" disc indicates not a lot of stopping repeatedly going on, therefore 6061 would be more then adequate, unless the calipers are really offset on the brackets, and I'm a big fan of overkill. I would not suggest welding on any alum caliper bracket, ever.

unless the calipers are really offset on the brackets

X2 - straight tension is best, if you need a big step go up on thickness.

they'll be pretty dog gone straight.

Why?

I had my brackets made for dual caliper with 1/2" 6061 T6 and I got the nut certs at Summit racing.I got the aluminum at metalonline.com

Clanton,
That looks like what I'm doing. I'm mounting 2 calipers on each: one 4 piston hydraulic, and 1 cable operated mechanical. This is a street car with a manual trans, so I want a parking brake. Also, I was at the Mopar Nats in '06 when that guy in the Dart lost his brakes and went off the end of the track. Not pretty. I want an emergency brake.

I use a hydraulic hand brake for e brake on 1 of the calipers.

I was contemplating doing that. How's it working out for you?

I tested it at the stripe[138mph 3900# car]with medium force slowing to about 40 a couple times and it did great.I have a hotter pad in the ebrake also.I would be interested in your cable parts list just for the info.

Wilwood MC4 Mechanical Calipers 120-12069-BK and 120-12070-BK. I have an old style floor mount E brake handle. Not sure on the cables yet.

5/16 aluminum is really wimpy. That isn't thick enough to withstand any sort of bending force. It might be okay if the bracket is loaded only in tension but I don't think I've ever seen a caliper bracket that is only tension. There is usually a couple of inches of offset from the bracket to the center of the rotor so the caliper is going to twist your bracket. After the bracket twists a few times it will crack or break which is bad. Even if it doesn't break it will give you a spongy pedal feel.

I appreciate the input. There is almost no offset. The center line of the rotor it is almost in line with the bracket. If I use any thicker material for the bracket the caliper wont line up with the rotor. I'm going to try attaching a sketch.

So I guess the .400" thick 4140 is overkill for my front brake caliper brackets?

1. the item has no redundancy if it fails, ie loss of on all braking on that hydraulic circuit
2. The potential great damage/harm to car, driver, others, by any crash caused by sudden loss of braking effort
3. For example, 6061 T-6 has a tensile strength of around 43K psi, in the welded zone , if not re heat treated, the tensile strength drops to around 11K psi
4. the rapid variation of strength from high to low back to high at/near the welded zone is an effective source for a welded induced stress riser.
5. Any welding induces some pre stress into the material iupon cooling
6. All alum fatigues, it fatigues at a faster rate as it is loaded closer to its limits, and in this case that limit varies greatly thru the welded zone
7. Alum fatigues even faster when reverse load, but luckily that only happens in this case when braking in reverse, but it does occur.

I would make the brackets from steel just for safety sake. and I wouldn't bolt two brackets together. make on bracket to hold the caliper that is the right shape and has more thickness.

Upon further reflection, I am not yet convinced our concern about flange deflection caused by caliper offset is really that much of a real concern. My reasoning is any deflection is initially caused by the caliper tightly griping a turning rotor, and if the caliper mounting deflects, the rotor or the caliper has to also deflect, )))edit((( However with the Op's 5/16" rotor, its not overly stiff say compared to a 1.25" thick rotor. And this is a rear axle set up and relatively has much less loading then a front axle.