1972 Mercedes 280SEL 4.5 Pressure Flushing Brakes

Is there some trick for pressure flushing the brakes in a 1972 Mercedes 280SEL? This is a beautiful and fully operational car but I want to flush the brake system with synthetic fluid but cannot get even a hint of fluid from the bleeders at any wheel. The brakes were all working well so obviously the lines are not plugged but I am wondering if there is some valve or solenoid that must be switched somehow. Please advise.

This is what I have. I was given one when I was at a Mercedes GTG a few years ago near Portland, OR.

http://www.peachparts.com/shopforum/diesel-discussion/117258-brake-bleeder-power-bleeder-homemade.html

It might even work on other makes.

Thank you. I already went through that posting but it all seems related to how to build a pressure bleeder and the pros and cons of pressure vs vacuum bleeding. I saw nothing related to my question but perhaps I missed it.

I am not a stranger to bleeding brakes, especially on vintage American cars, but on my 1972 Mercedes 280SEL 4.5, nothing comes out any of the bleed valves when the brakes were working. I can image one line being plugged but certainly not all of them! Because nothing came through, it seemed that perhaps some device needed to be actuated/deactivated or perhaps even the ignition needs to be on and this is what I was asking. I've reviewed online how-to videos for old Mercedes but there was nothing mentioned like that so I'm not sure what might be wrong.

There's nothing mysterious about the system. There should not be any electrical solenoid. Your bleeder screws are probably plugged. I've owned 4 Mercedes W123 series cars and I'm more than sure they were the same. The brake cylinders have a tendency to freeze up if the car has sat for a long period time. It has something to do with the moisture that gets in the system which is why Mercedes Benz requires flushing the brake system every couple of years.

I was hoping that was the case although it's still a mystery why the fronts also do nothing. They have freshly rebuilt calipers with new bleeders and hoses. I didn't touch the rear but knowing that there is nothing else to look for, I'll pull out the bleeders and check them more carefully. I think I actually have a pair of new bleeders but haven't installed them yet.

It turned out that the rear flexible lines were totally collapsed inside and wouldn't even pass 100lbs of air pressure! I had a new one for the right but the car needs two so I ordered the left side too. It should solve the problem and thank you for confirming that there wasn't anything special that it needed. My expertise is in '40s, '50s and '60s drum brakes.