What I want to know is “Why” on these cars? They’re certainly not the only car, or brand to use a rotor on a hub, and yet here we are with a car that you have to be almost **** about a simple brake change to avoid crashing when the brake pedal goes away.

94+ mustang is a full 4 rotor on hub car, and on all of the web forums, there is never an instance of brake issues that came as a result of failure to check runout. Granted A 90’s era car is 12 years newer than the last C3, but when the smoke clears, it’s still a freakin rotor, bolted onto a machined hub face, held on w/ lug nuts. From the factory, ford held the rotor onto the hub w/ a simple lock collar that slid over the stud. No bolts, no rivets.

At what generation does Chevrolet finally fix this issue, and what did they do to fix it?

 

Its not the discs. 65-82 Corvettes have fixed calipers. Almost all cars, including C4s, C5s, and non-Z06 C6s, have floating calipers.​​​​​​​​​​​​​​My 2022 Mustang has huge Brembo fixed calipers, in the front only. I bet your 94 has single piston floating calipers. ​​​​​​​Also, new cars have hub assemblies that are replaced as a unit.​​​​​​​​​​​​​​

 

The front rotors are bolted on 2 piston Cobra calipers, and the rears are single piston floaters.
you’d think there’d be a kit to “float” the C3 calipers given that the next Gen cars did it then.

 

Next gen cars were made to be Cheaper, not better. GM uses fixed calipers, with bolt-on, non-serviceable hubs, with their sports cars again (and the C8, too)

 

I dont bolt or rivet on new rotors. Just let them float, the caliper holds them in place when the wheel is off, and the wheel sandwiches it in place when installed .

 

The 94 Mustang Cobra calipers are floating-type, BTW. Once the wheel is installed, and the lugs tightened, all rotors are bolted to the hubs.

 

The Corvette disc brake design is actually quite good and was well-designed given the early-'60s material and manufacturing limitations. The same could be said of the independent rear suspension; Chevrolet upgraded to lightweight aluminum and better design as materials and manufacturing made it economical.

I believe we are also seeing shade tree mechanics introduce problems based on ignorance of the fixed caliper design's intolerance to run-out while thinking all disc brake designs are the same. Even reinstalling a true-running rotor in a different orientation will likely increase run-out to say nothing of a replacement rotor that was machined separately from the hub and just installed any old which way. This is just one of the quirks and challenging aspects of keeping 50-60 year old technology on the road.

Does anyone know the disc brake designs of other GM lines at the same time as the C3 run? In other words, when did floating calipers come into production for any GM line?

 

The 1970 Camaro was the first GM car that had front disc brakes as standard equipment with no drums even available. And they were single piston floating calipers. Drums in back.
Some of the 68-69 Camaros had front disc brakes, drums were standard, and more common. Some versions were 4 piston fixed caliper and IIRC others were single piston floating caliper.
I think that part varied when they had either 2 or 4 wheel disc brakes. No idea on the 67s.
Not sure about other chevies.

 

That's the whole game, right there. My 2003 Cobra had, and current 2016 Mustang has multi-piston floating calipers on all 4 wheels. If the rotor has a bit of runout, the caliper moves with the rotor when the brakes are engaged so there is no air pumping issue. That and floating calipers all used O ring seals from the get go. The reason is explained in an article at the link. You might find this interesting.

https://www.duntovmotors.com/tech-calipers.php

Unless you pull the hub, attach the rotor and mill the rotor in a grinder (not a lathe), you probably won't get the rotor runout close to zero. Not a big deal to do up front, but as all of you know, pulling the spindles out back is a bit of a PITA.

So how much runout is too much? Any amount that pumps air into the calipers during regular driving. If your brake pedal stays firm over an extended period of time, you probably don't need to worry about rotor runout. I had to replace an original front wheel hub last summer. Drilled out the rivets, put the original rotor on the new hub and reassembled the brake/wheel, with only the lug nuts holding the rotor onto the hub. I didn't even bother to check the runout. Four months of driving later, no air in the caliper. I'm about to replace the wheel hub on the other side, and will do it exactly the same way. I don't expect any problems.