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A pressure bleeder will do that very thing more easily and with higher pressure. However compressing the brake fluid with the pedal should also dislodge bubbles that can move to the highest point and they can then pass through to the reservoir when the pedal is released.
Reverse bleeding can be helpful but it can be difficult to get a good seal at the bleeders.
If all else fails you may find your master cylinder is pooched. The OP in this case has changed his MC but it is worth noting that in the process of bleeding brakes some people damage their MC seals when the pedal goes down farther than usual. This forces a buildup of crud on the piston past the MC seals.
I do not know what happens if you try to trigger the ABS pump, perhaps using a switch in place of the relay. It should be possible and possibly helpful to bleed at the fittings at the ABS pump with a pressure bleeder in place though.
It'd be pretty awesome if you could fill the res up or fit a pressure bleeder with a good supply of fluid and then go around with a pushbutton switch wired to the relay location, at each wheel giving the ABS pump a poke and bleeding the brakes under pressure using the ABS pump.
-Joel.
Joel Frahm
1992 968 Cabrio Black/Cashmere
1994 968 Cabrio Iris Blue/Lt. Grey - Supercharged
1987 928S4 Diamondblau/Blue
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The inside of the brake master cylinder could be corroded/pitted from age stopping the piston from holding pressure. I just had the same thing with my clutch master cylinder. Its work fine for the last three years, but once disassembled during my engine rebuild it could not hold pressure. On closer inspection, the inside wall of the cylinder was pitted from old age/ standing moisture.
89 944 S2 - Promax Chip - sold
92 968 Cab - Airbox Mod, RS stage I chip.
18 Jaguar V6 P380
