Hi, Really at my wits end with this car. Bought this 1984 500 SEL about a month ago. The car had sat for approx. 1 year. A DIYer I put new pads, rotors and two new calipers on. This car also has the ABS. Bled brakes and pedal slowly went to floor. Stopped the car but took some pumping. I don't plan on driving till I have a good pedal.

I thought the problem was the master cylinder. Put that on 2 days ago and still no hard pedal. Lines are not leaking from what I can tell. Old fluid is out of the lines since all clear brake fluid is coming out the bleeder screws. Had a friend pump the brakes and belief we consistently followed the correct procedure to insure no air got sucked back in. Intially there was a great amount of air, but that has been quite awhile ago.

Then today, we bled again with engine running. Still no air is coming out, just fluid yet no hard pedal. Is is possible to have bought a bad M/C? Should the car be tilted any certain way? How can air remain? Any ideas would be a blessing! Thanks
Bill

definetily you could have gotten a bad master cylinder. if it doesn't feel right after you pump it up & is still soft, try another master cylinder.

Did you bleed the ABS? I am not an expert in this but I do know there is a separate bleeder screw on the ABS unit. I don't know if failing to do this could possibly be causing your problems, but might be worth a look at the CD before condemning the master cylinder.

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Steve
'93 400E

Hard to tell about these things, but more than once I've driven a car and seated the pads that the tech thought he had a bad master cylinder. If you are getting a pedal on both sides of the system you could have this situation.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

I haven't bled the ABS. I took the cover off and only found fuses and wires to the system. I don't have a CD. I had cracked the line after the ABS once and fluid came out. I figured that was good. I will look again for some type of bleeder screw.

A friend suggested that I try to isolate the problem by making some sort of plug with some new brake line. First at the M/C, then after the ABS etc. Maybe narrow it down to the front or back or a caliper. Sounds like its worth a try.
I'll let you know....
Bill

possible rear calipers swaped with the
leeders pointed down? just a thought

I plugged the two ports leaving the ABS for the front brakes, so fluid was just going to rear. Tried the pedal and discovered I had a hard pedal. I am now thinking that the front driver's caliper is bad. I will replace that and both front brake hoses and a new bleeder screw on the passenger side and see what that does. Master cylinder and ABS must not be problem since I got the hard pedal after plugging.
Bill

It's not uncommon on more complex brake master cylinders to trap air in the master cylinder itself. It's often suggested to bleed the master cylinder on the bench before installing. In lieu of that have a friend press the pedal while you crack the brake line fittings, one at a time, at the master cylinder.

If you find that you've solved the falling pedal by doing this, check to see what happens if you press hard on the pedal for sometime. If it gradually falls, you've still air in the master cyylinder somewhere and may need to do a pressure bleed with one of those master cylinder attachements.

Good luck.

Ben