Brakes won't work

[Joe]

I'm trying to get the brakes to work on my 1965 stick 230SL The car sat for two years before I got to working on it.
After replacing the master cylinder and reservoir, and rebuilding one rear cylinder and one front caliper, the brake peddle goes to the floor.
I also replaced the front pads and all four rubber brake lines.
There are no leaks in the system.
I've run at least three quarts of brake fluid through the bleeders. I get flow through all four.
Today, I removed the three lines from the master cylinder (MC), and put bolts (M10-1.50) into the holes. The peddle would go down about a half inch. This indicated to me that the MC had been bench-bled ok (by me).
I drained the rear reservoir and put the rear brake line back on the MC. Added fluid. Brakes are down a bit, but the peddle is close to the top.
Removed the bolt to the right front wheel and put the line on the MC.  Added fluid. Brake peddle goes down about 75% of the way to the floor.
Removed the bolt to the left front wheel and put the line on the MC. Added fluid. Brake peddle goes down to the floor. as before.
Bled the front brakes with a power bleeder. Fluid and few bubbles came out. After bubbles stopped, tightened the bleed screw. Did both front wheels.
Still the same result.
I've also bled the four wheels with a pressure bleeder, with tno improvement.
It was my understanding that with a dual-circuit system, the brakes would still work if one circuit was lost.
Any advice is appreciated  in helping solve this very frustrating problem.
Joe

[Rodolfo]

A sealing in the master cylinder mounted backwards ?

[ctaylor738]

Sounds like you have your front calipers on the wrong sides.  The bleeder should be at the top.

[Joe]

Chuck, you're a genius!
Thanks!
Now, why don't the brakes work if one circuit is operative?
Joe

[ctaylor738]

Not sure I understand the question.  If you are asking why the brakes won't work with the calipers upside down, I would say that with that much air to compress in the fronts taking all the pressure, there isn't anything left over for the rear circuit.

If you have the front calipers on correctly and are still having problems, please be more specific.

CT

[garymand]

He's asking why the backs didn't work despite the front's failure.  My experience with that is not with a benz but with a Triumpth: a piston inside the master cylinder pops forward or back to block the fluid flow to the leaky half.  The Triumpth had a ball switch sitting in the middle of the pop valve, when the valve pops the switch is closed to tell you through a dash light that yuour beaks have a problem.  To get the piston to pop, you have to hit the break pedal hard enough to pop the valve over.  If you don't stomp the pedal, the valve won't pop over to close the passage.  I think it was a separate but parallel passage to the main master.

Once you pop the vavle, you have to up-pop it to get the passage opened.  Not sure what MB does, but it would have to be in-line to the two master pistons.  I remember a spring separating two pistons and seals...

[ctaylor738]

Did this get straightened out?

[Benz Dr.]

I've put calipers on wrong once. Pretty quick lesson learned.

  You should also check the free play on the brake pedal. There an eccentric bolt right beside the firewall pad on the pedal linkage; the head of this bolt has a small groove that should point towards the fiewall. If it's in any other position than straight back you will end up with excess free play on your brake pedal. Normal free play should be about 19mm.

[Leadfoot]

Sounds like the master needs to be bled first, if there is air in the master, you can push gallons of fliud through the calipers without getting any decent peddle pressure. This would also explain why you are not getting any rear brake pressure while the fronts were installed incorrectly.

use a short bit of brakeline with the proper fitting, screw it into the front port on the master, make sure it is bent in a manner that will aloow it to end in the brake fluid in the master, slowly pump the brakes until the air bubbles stop, do the same for the rear fitting on the master. Reattach the brake lines and bleed the brakes and you should be good to go.