Just installed a 15/16th piston MC on our 70 Challenger. Awaiting new front disc pads to arrive to replace the very soft and dirty pads currently on car.

They were being used because with any cleaner pads, I had almost no front brake action on this non power brake car converted from front drum to front disc,,,car retains rear drum.

I did bench bleed new MC very well, brakes are much better than before, but must still bleed at each wheel as likely got some air in lines when I broke them from old MC to attach to new MC,,,brakes are full pedal, very slightly spongy but still ok.

Question. While awaiting arrival of new pads, if I were to bleed only rear brakes today, are the front brakes completely and totally isolated from the rears so that if I should drive the car that I can assume that I would not be required to bleed the rears again when I bleed the fronts later.

I plan to bleed the fronts once I pull the wheels and replace the pads.

Don't believe that I had ever considered this issue before,,,,likely others have.

I would bleed all 4 wheels and then when you replace pads' remove some fluid from MC, so it doesn't overflow when you push the pistons back into the calipers. I wouldn't chance driving it with the possibility of air in the system. Good brakes are WAY more important than more horsepower! lol

Actually was more a theoretical question of a curious mind that had wondered about it before. Don't really plan to drive,,,,did drive a short test to ensure that all was well and that stopping power of front disc had improved. It had.

Anyone else ever wondered on this or have an opinion?

On most muscle era MOPARs there is no connection between the front and rear systems. The master is divided and the output lines do not connect. I think it would be OK to bleed separately. I would probably hit it again though when the fronts are done. I prefer to bleed, let the system settle so any small bubbles collect and hit it again.

Correct, as said they are totally seperate, which was the intent of Ma in '67 (Model Year) with the intro of the dual bowl & therefore the dual system for better safety for as you know if one side sprung a leak you'd still have half a system whereas before that you'd have no brakes just an ebrake. Just be sure to bleed the MC first for whichever half you are working on before you bleed the 2 corners for that specific (MC) half. Put a block of wood under the pedal to keep the MC piston cups from going past thier normal travel (wear) area in the bore

When I posted the question awaiting my replacement pads, I still original pads in the front discs. Just wanted to bleed rears while waiting.

What really triggered the question was that when brake bleeding is discussed, you are always told to start with wheel most distant from from MC, which is usually RR and the LR and so forth. It would appear with dual reservoir systems that you can safely ignore this.

As an aside when using Wilwood calipers for whatever their reasoning they choose to use a non-standard bleeder valve,,,much smaller. You find this out when you go to hook up the adapters for your vacuum pump bleeder system and find you have no adapter to fit securely. Would be gentlemen like if they would inform you of this. While on the topic, would be nice if Mityvac in their overpriced compressor powered bleeding 6835 system would include the smaller required adapters instead of sending you 4 standard adaptersthat just cause you to suck air instead of brake fluid.

But this would mean that their engineers and marketing gurus would have to come out and see what us chickens out here before foisting their next great idea on the unwary who buy their stuff and keep them in business.

Wilwood builds race oriented stuff. Smaller = lighter. Lighter = better.

Worry about the ounces and the pounds take care of themselves.

Correct, this got burned into peoples' brains back in the years' when all 4 corners were connected (pre 67). Just be sure to bleed the MC first