Help with 83 911 SC brakes

[deeking55]

Good day! I finally swapped out my old calipers for some new PMB rebuilt ones, bled the system 5x all the way around and I am still getting a pedal to the floor. No leaks at any of the lines or bleeder valves, no air bubbles when I bleed the calipers. I had the Master Cylinder empty for at least 6 weeks waiting on the brakes, I am concerned my master has now failed or some internal seals dried up while it was empty. Is there anything I am missing here? I've bled brakes multiple times before and I am confident the issue is not air or poor installation. I can't think of anything else that would create the failure. As far as I know the MC may be original.
thank you so much-

jason

[deeking55]

Addendum - Rubber lines are all new
I have a line coming out of the transmission tunnel that is disconnected, would loss of vacuum cause this problem? And where does the line go to?

[Flojo]

Originally Posted by deeking55

... I am concerned my master has now failed or some internal seals dried up while it was empty.

guess that's it. bad seals dried out or ripped now when fluid flush with too much pressure.

[MBAtarga]

I searched and couldn't find the thread(s) that came to mind.
There is a possible issue if the master cylinder piston extends too far into the bore when bleeding the system. IIRC, something about the forward seal can be scratched from the cylinder wall if it is extended too deep.

[merlinfe]

Deeking,

How exactly did you bleed the brakes?

Are the calipers on with the bleeder screws pointed up?

Are you 100% sure the lines are all tight?

I only ask because I had trouble bleeding my brakes on my ‘83 as well and in the end it took 4 complete cycles with a power (pressure) bleeder to really get the pedal feel perfect. This was after the buddy method and the vacuum method at the bleeder.

Let us know,

-Steve

[Zaz]

May need to bench bleed the MC

[deeking55]

Thanks all. I did the 2 man method with my father which we have done multiple times before. Pump up brakes, hold pressure, release bleeder, fluid out, retighten bleeder, release brake pressure. Multiple times per caliper multiple times around the car. Lines are tight with zero leaks.
Now that I look at it, my rear caliper bleeders are topside while my fronts the bleeders are down. Are my front calipers reversible - did I get them put on the wrong sides? And this would make the difference?
I'm not clear on how bench bleeding MC makes a difference when I never had it out, fluid level was never below 1/2 and I have good pressure and no bubbles from bleeder valves.
I do think my vacuum line is off but I believe that had happened prior to all my brake work, my SC has been backdated to carbs would that make a difference?

j

[Bill Douglas]

Originally Posted by deeking55

Now that I look at it, my rear caliper bleeders are topside while my fronts the bleeders are down. Are my front calipers reversible - did I get them put on the wrong sides? And this would make the difference?

Yep, that's it. I did the same thing on my SC so you're not alone. The right way up will fix it LOL

[da Vinci Dan]

Bingo - can’t bleed if valves are down. Air is still caught above.

[deeking55]

Wow, amazing the difference! Significantly better pedal feel after evacuating that air with bleeders pointed up. Still not hard pedal feel I had before I dove down this hole. Will that improve with pad/caliper break in or do I need to continue bleeding?

j

[mepstein]

A lot of times they will improve after you drive a bit, bed the pads and then bleed again.