Now my brakes are worse than before!
 

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?

It it still taking on fluid? If so there's a leak somewhere.

I'd say a new MC if all the lines/hoses are good. Shouldn't be too bad for a rebuilt unit, around $110 IIRC

Yeah, if you're losing fluid and can't find a puddle, its draining into the booster, new m/c time.

It's not losing fluid unless I'm bleeding it. I ran a lot of fluid through it trying to bleed it out, but it's not losing any otherwise.

I'd bleed the rear brakes too. Also be sure to check the level in the mc resorvor. If low it would make trouble.

Just sounds like a bleeding issue.

I'd bleed the rears before replacing the MC.

I have read that sometimes the two man bleeding technique can push the MC piston past where it has "worn in" to a region where the bore of the MC can be corroded, so that you create an internal leak. Long shot and hard to check, I know.

Best bleeding method is a Motive Power pressure bleeder, IMHO. You can DIY and get a good bleed pretty easily.

Rgds,
Chris W.
'95 E300D, 391K

the rear brakes
 

I would def. bleed the rear brakes too. i did a caliper change on my VW for only 1 tire but because a lot of fluid spilled by accident while doing it, I think i let the MC run either low or empty before I put in some fluid and air might have trapped in the other lines too. I got symptoms like yours even after I had bled the one caliper I had installed multiple times. Eventually I bled the other 3 calipers and sure enough, two of them had some air in them. That solved the problem. I don't know the system well enough to know if air can get trapped in other lines or not, but it worked for me.
Also, make sure you are doing the procedure correct. Open the bleeder screw while there is pressure on the brake pedal . Then tighten it before letting go of the pedal. That way, no air is being sucked in through the bleeder screw opening.
Hope it turns out ok !

You still have air somewhere, possibly in the master cylinder, if you let the fluid get too low during the bleeding process. I don't know the bleeding procedure for your master cylinder. Some will self bleed over time and some require special lines hooked up temporarily to recycle the fluid into the reservoir.

Yeah, your talking about what's called a bench bleed of the master cylinder. I never ran it even close to dry, so that shouldn't be neccessary I don't think. It will be soon though, as I'm ordering a new master cylinder. Just came in from bleeding the rears and no dice, pedal is still as soft as butter in August. It might even be worse than before. I don't know what else to do.

Now when I bleed I use a clear line fitted over the nipple and an elevated catch can, so it can't suck air back in because the line is full of fluid. In any case I saw no bubbles during this bleed. If there is air in there, I sure don't know where it is.

I went through the same thing recently on mine. Multiple bleeds, same erratic soft pedal. I put in a new MC and it's all good.

As soon as you get air in the MC then pumping only makes things worse as you are making smaller and smaller bubbles. Power bleed it from pass rear, driver rear, pass front, driver front.

And as others have said, old MC may never bleed. I DREAD every time I have to crack the line.

yup.
once you get the new MC, I STRONGLY recommend either you purchase a motive power bleeder, or you build a power bleeder. it's SUPER SUPER SUPER easy to use and bleed the car with one.
I mean REALLY easy and fast and you KNOW it's done.

For me any power bleed device is just another high maintenance tool to care for. I bleed seldom enough it is no trouble getting the Mrs. to help.

High maintenance? in what way? it's a jug you put brake fluid in, and pump up...

um?