Car: 1982 240d, manual transmission.

Background: For a while now I've been getting some grumbling from the front brakes on longer braking cycles such as off ramps and whatnot. Additionally, the brake pad wear indicator light would sometimes come on. So two weeks ago I did an inspection and found the driver's caliper had a piston sticking, uneven wear, worn pads and nearly 2mm of lip on the disc, the passenger side showed even wear, worn pads, cracked piston seals and also nearly 2mm of lip on the disc. So these brakes were done. I ordered a bunch of parts.

The repair: Last weekend I tore the front end down and replaced everything from the spindle out except the hubs themselves. Bearings, rotors, calipers, pads are now new. I took the opportunity to upgrade to to vented early-W126 discs and calipers. Everything went together without a hitch. I bled the brakes using a two-man pedal pump method.

The problem: Now my brakes are soft as can be. I expected a difference in braking, but not like this. The pedal is just soft and spongy, even with the engine off. I can pump it up and make it firm, but it slowly drops and gets soft again. I bled the system some more, a lot more. I mean I ran nearly an entire bottle of brake fluid though it. I used a clear hose attached to the nipple and a bottom suspended above it to catch the fluid, no bubbles come out since the first time I bled it. I have not bled the rear brakes. The rear brakes were redone about a year ago and I used the same methods as above to do the job. It went off without problem. I'm guessing master cylinder but I figured I'd ask around before spending more money. Any thoughts?

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Own:
1970 Mercedes 250c, 1976 International Scout II, 1982 Mercedes 240d, 1997 Honda Accord Wagon, 1998 Acura Integra Type-R, 2009 Mazda5.
Owned:
1974 International 100 pickup, 1975 International Scout II, 1981 Mercedes 240d, 1985 Mercedes 300SD, 1988 Honda Accord, 1988 Ford Thunderbird, 1991 Honda Accord, 1996 Geo Metro, 1996 Ford F150, 1996 Dodge Grand Caravan, 1997 Honda Accord, 2003 Acura TL-S, 2003 Yamaha V-star.