Did air get to master cylinder?

[Discseven]

Just replaced rotors, calipers and pads on '80 SC and bled system RR/LR/RF/LF as is standard. (Soft brake lines all around were replaced with new less than a year ago.) Used almost 2 liters dot 4 with a Schwaben pressure bleeder.

Pedal is hard with engine OFF. With engine running... pedal's mushy but brakes do work to stop car. Only moderate braking was tested.

I've now bled system again using an additional 1/3 liter dot 4. Same status. Took up some pedal slack by running out the linkage rod (that runs up from pedal cluster.) Ok... some pedal slack is gone while mush remains.

Reservoir did NOT run dry during bleeding---this I know for sure.

Only thing I can think of is when I removed the right rear caliper, I did not plug the brake line so fluid was free to drain while rotor & caliper swap was made. I decided afterwards that leaving the brake line open-ended to drain might not have been a good idea so I plugged the remaining 3 brake line ends while swapping parts.

... Did leaving right rear brake line open to drain allow air to back up into master cylinder---can air back up into cylinder? If this is possible, what's the fix? Is pressure bleeder strong enough to force all the air out---I used no more than 14 lbs max. If not air in master, then what?

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[Targalid]

Probably need new seals in the master cylinder. When you bleed the brake system, pushing the pedal beyond its previous range of travel forces contact between the rubber piston seal and the rough surface of the lower master cylinder. It makes micro cuts in the seal and it allows fluid past giving a mushy feel. I did the same thing. It is possible to put a wooden block below the pedal to prevent excess piston travel during bleeding but most people forget to do this. A new master cylinder is about the same price as a new seal kit.

[yelcab1]

Did you put the calipers in upside down?

[Discseven]

Originally Posted by Targalid

Probably need new seals in the master cylinder. When you bleed the brake system, pushing the pedal beyond its previous range of travel forces contact between the rubber piston seal and the rough surface of the lower master cylinder. It makes micro cuts in the seal and it allows fluid past giving a mushy feel. I did the same thing. It is possible to put a wooden block below the pedal to prevent excess piston travel during bleeding but most people forget to do this. A new master cylinder is about the same price as a new seal kit.

Good note on seal preservation TargaLid---thanks! But did not go pumping brake pedal route. Used pressure bleeder. Am doing this solo.

Originally Posted by yelcab1

Did you put the calipers in upside down?

Of course. They look better.


Came across this...



Did front left to reservoir. Then rear right. Pedal is stiffer but there's a conundrum... did NOT see any air pass through return hose---front or rear. Will step back and check pedal later today.

Meanwhile... any comments on topic are welcome.

[911 Rod]

With the car running does it feel the same as before?

[Discseven]

Originally Posted by 911 Rod

With the car running does it feel the same as before?

That's a fine wake up call Rod. With engine running, pedal is distinctly tighter than when I started dealing with issue this morning. Still, if there was air in master and "loop bleed" remedied that... I'm stuck on how I missed the air going by (in a clear hose.)

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[Discseven]

These refs are not Porsche specific. Am looking at them for principles.






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