87 300sdl brake question

[exdies me]

I changed the worn pads and rotors on the front of my SDL, before I had no problems with the response of the breaks. After replacing the brakes I noticed what I believe to be air in the lines, so with the help of another we bled the lines starting passenger rear, driver rear, pass front, driver front, after bleeding the lines I noticed that the pedal would slowly go to the floor and not hold pressure or stay firm. I could not find any brake fluid leaking.
Is the master cylinder bad, and is this a normal problem with this car, How can I make sure this is the problem, and is there something else I could do to to check it out. Thanks ahead of time

[Brian Carlton]

I'm going to hazard a guess and say that the reservoir fooled you.

On this vehicle, you must look at the reservoir from the passenger side. From the driver's side, it appears full. But from the passenger side, you can see two distinct chambers and just a bit of bleeding at the rear brakes will run the rear chamber dry. It's capacity is a fraction of the fronts.

I've struggled with bleeding the rear brakes on this one. Recently did it and I still don't like the feel. Have to bleed them again. But, you only get about 10 presses of the pedal and fluid must be added. It has to be done carefully so that it spills over into the rear reservoir. A real PITA.

[t walgamuth]

those symptoms it also could be an internal leak in the mc. if it is leaking past the primary piston seal it wont leak on the ground but your pedal will sink as described. it may have been doing it for a while and you didnt notice it til you did t he work and were scrutinizing the perforrmance.

tom w

[Ara T.]

The pads may not be seated yet, I experienced this when I did the pads on my 300D... it took about 2 or 3 days to break them in, follow the directions from the manufacturer on how to seat the pads.