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So finally got my Alfetta through smog and running and so of course that means something else has to fail which in this case is the brakes. The pedal began going to the floor on some stops. Then it would work ok for awhile. Then it starting going down more frequently. With as bit of pumping and patience the brakes seem to work ok but the pedal going flat to the floor does not inspire confidence. All of this happened in one day so it went downhill pretty quickly. Now the pedal is low all of the time. Again, the brakes still work but with the pedal to the floor so it's hard to tell if they're actually lacking any power but I would say they aren't as strong as they were with the full pedal.

Also, the reservoir is full and there is no sign of leakage from the master cylinder or brake lines in the engine bay. I replaced the MC not that long ago but can't remember if it's new or used or where I got it. It's a 22mm Mac and I removed the safety check valve also as it was leaking and I couldn't find a replacement.

Could it be anything other than the MC?. And can the MC be this bad and not leak externally? I know they often leak into the booster but if the MC is bad, does it always leak or can it just leak internally past the piston seals?

Thanks
 

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When our 78 Alfetta sedan had the same thing happen, pedal sinking to the floor, but pumping bringing it up, and again sinking, etc, changing the master cured the problem.
 

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It's just as you called it superloaf
They are the classic symptom of worn rubber cups in the master cylinder. the cups wear this allows the brake fluid to pass over and behind the cups filling the void made when the piston travels forward. this is why the pedal drops, when you release the pedal the piston returns to its original position and so does the fluid .the fluid does not always leak out it just travels up and down the cylinder bore moving from one side of the rubber cups to the other. some fluid is pushed to the calipers just not enough .
 

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Well... It's still possible that the pressure cups are leaky but the seal is not; though hardly possible because they're made of the same material that ages. I'd check the booster for fluid if possible.
... and I removed the safety check valve also as it was leaking and I couldn't find a replacement.
Thank Volvo, there is a cure for this valve on the market, I've posted a little about it:
http://www.alfabb.com/bb/forums/alfa-romeo-parts-sale-wanted/377169-69-roundtail-brake-line-parts.html#post6007025
It's exactly M10x1.0 thread, same flare type; all you need is a set of threaded plugs (from online metric hardware stores) and copper washers.
 

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Discussion Starter #5
Well... It's still possible that the pressure cups are leaky but the seal is not; though hardly possible because they're made of the same material that ages. I'd check the booster for fluid if possible.

Thank Volvo, there is a cure for this valve on the market, I've posted a little about it:
http://www.alfabb.com/bb/forums/alfa-romeo-parts-sale-wanted/377169-69-roundtail-brake-line-parts.html#post6007025
It's exactly M10x1.0 thread, same flare type; all you need is a set of threaded plugs (from online metric hardware stores) and copper washers.
ThAnks, everyone, for the info and thanks for that Volvo valve. I'll check the booster for leaking fluid just to confirm and then plan on replacing the MC. Or maybe I'll try the rebuild kit. Tired of sinking money into this unappreciative car....
 
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