I am having a most depressing experience after having replaced the master cylinder on my wagon. Things are not improving. My self esteem is in the dirt.

To recap. Replaced my non ABS MC with a new one, not rebuilt. Did not bench bleed. Bled all lines using my vacuum bleeder. Focus was on replacing all the fluid. Bled till well past no air being evident. No good. Pedal sunk about 2" before getting firm with no power, and would not pump up. Sunk nearly to the floor with very poor braking with the engine supplying vacuum to the booster. Concluded I still had air in the lines, but puzzled because it wouldn't pump up.

Re-bled everything the conventional way - stick propped against seat - following the Bentley mantra for Volvo brake bleeding. Pedal still no good. Enlisted the wife's aid, with yet another quart in hand. Nada. Got a motive power bleeder and a gallon of DOT 4 and did it all again being very liberal with the brake fluid. Nope.

You can read details of the first half of my tribulations at http://brickboard.com/RWD/index.htm?id=914021&show_all=1.

Also, jacked the rear of the car nearly three feet up then gently rattled the proportioning valves with an air hammer in case they were stuck. Nope. Pumped up the system and let it sit for 10 minutes pressurized, then bled each rear alternately. Repeated for hours, literally. No dice.

Disconnected the rear lines at the differential pressure switch and plugged the ports just to eliminate the rear system. Pedal improved, but only about 50%. Reconnected and re-bled.

Thought a bad MC was unlikely, but ordered another new one just to be sure. Then had a nasty bout of the flu after which (and the bronchitis that followed) I had to get an apartment rent-able. Finally got back to working on the car today.

Bench bled the new MC this time, canted 45° to the left to get the ports at the top because they aren't tangential to the bore. Got every last scrap of air out. Actually, foolishly, began to harbor some hopes this was going to work.

Bolted MC onto booster, attached lines while allowing MC to drool all over to minimize any likelihood of air re-entering via the ports. Bled the entire system according to Volvo's green book this time - smooth strokes with all bleeders flowing through flooded hoses to beneath the surface of fluid in old brake fluid cans (got plenty of those!), starting with front left, front right - all of 'em, rear left, rear right.

No good. Pedal is a little better but not much. Still sinks nearly to the floor with vacuum on the booster.

Re-bled everything using the Bentley formula - rear left, front left upper, right front upper, etc. Ran the rest of the quart through. Nope. Got out the Motive and ran most of another quart through. No signs of any air at any point. Nope. Did it again with the Motive while pumping vigorously on the pedal. No luck.

All calipers are installed correctly, bleeders at top or middle as appropriate. All caliper pistons are correctly up against the pads which in turn are correctly up against the rotors. No lost motion swallowing up fluid. All work performed on a basically clean garage floor - no leaks of any kind anywhere.

So what the screaming %&*#@!!!??

Unless someone can hand me a clue here tonight or tomorrow I have to throw in the towel on this and pay someone to figure it out. It will be a first for me for anything but an alignment or car tires. I have always done my own work on everything.

To be humbled by a brake system. I can't show my face in public. I'll have to use an alias at a Volvo joint in some town far from here and beg for their help, prostrated, placing their feet on my head.

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For anyone who's interested, both the primary and secondary pistons, misleadingly named, have an effective area of about 0.3 in² and a stroke, if I recall my measurements, of about 1.3".

If one piston fails, that half of the system is gone. The remaining piston cannot supply pressure to the system fed by the failed piston. Doesn't matter which failed. Hence, there is no primary or secondary in my way of looking at it, just two pistons sharing a bore.

A stepped bore, you might note. Primary bore is about 0.877" I.D. and secondary right around 0.62" I.D. Too lazy to get out a bore gage so I measured on the squish of the secondary's O-ring. Primary has a cross sectional area a touch over 0.6 in² and the secondary 0.3 in². As the the two pistons move down the bore about half the fluid displaced by the primary fills the void left by the secondary receding down it's bore, leaving only about 0.3 in² actual displacement. Thus, both pistons supply basically the same amount of fluid to their respective systems despite the difference in bore diameters.