ep4

I recently changed out all the brake pads and rotors on my 2002 E320, and bled the system. The pedal seems to have long travel before the brakes engage and it feels a little mushy.
Here's a little background. The car had a great pedal and stopped very well for a few years, then I decided to change the pads. I replaced front and rear, and we bled them using the two man method. The pedal was not great but the car stopped well. We did this 2-3x and it never improved. The fluid was completely changed out.
The car was driven this way for a year or two, and I decided to change the pads and rotors this time due to some pulsing when braking at highway speeds.
I ordered the brakes and replaced them all. I opened the bleeders when compressing the calipers, as not to push any fluid back into the master or abs. We bled with tow guys again and the pedal had long travel and seemed a little mushy. I decided to purchase the Motive pressure bleeder and try it that way.
Yesterday I put about a quart of fluid in the bleeder and hooked it up to the master. I pumped it up to about 27-28psi and bled the brakes again, RR,LR,RF,LF. I noticed the fluid seemed to come out a little slow from all the wheels, but it was steady. I did keep checking the pressure and did my best to keep it at 27-28 for all 4 wheels. I drove the car when done and the pedal still feels bad. I am not sure if I should have pumped the pedal until it firmed up, before I started, or if that makes any difference.
I read about checking the booster function by pumping the pedal with the engine off, then starting with pressure on the pedal. When off the pedal firms in a few pumps. The pedal drops when I start the car with my foot down. I can hear a slight swoosh when I am pumping and pressing the pedal with the car running. It's not a leaking sound, just a swoosh of air when the pedal is pushed down. The car stops great, so the brakes are functioning well, it's just the pedal that I can't seem to get to firm up and come up a bit.

kajtek1

You need to learn a bit more about the brakes on your car.
It is equipped with ABS/ESP pump and reservoir that is closed unless computer activate it.
Those brakes should be pressure-flushed with what I remember 35psi.
Whatever you did, you have air in the system and if DIY pressure bleeding will not clear it, you need to find mechanic with SD and do the flush with computer.

ep4

There was never any fluid pushed back up into the system when they were bled and the reservoir never went dry at any point, so I would not think air has been introduced into the system. The standard pumping and bleeding process may not be the best method for this car, but I still can't see how it would put air into the ABS/ESP.
The Motive bleeder only goes to 30psi, and it seems a lot of people use it on these cars. i read 2 bar was the recommended pressure, is that not correct?
Do you feel that pumping the brake prior to pressure bleeding, makes any difference? Can the brakes be bled with the ignition on, or would that make any difference? It would be helpful to know if there is something missing from my procedure, that could help.

kajtek1

I was using 40 psi on one of my cars that I wanted to flush very well- as at 30 psi the fluid barely go.
Anyway, we can speculate how did you get air in the system, but sounds like an air bubble made it into ABS reservoir and you will not get it out without SD.

ep4

Most vehicles will actuate the abs when you panic stop or during hard braking, especially is sand or on wet pavement. When the pump runs, it normally pushes a potential bubble out, and then it can be bled out of the lines. Would the Mercedes ABS not function the same way?
I also read a post where a member said he installed a new master cylinder and bled the abs at the lines coming out of it, while bleeding the brakes. I am not sure if that works or not, but he said he had success with it. Thoughts?

kajtek1

Seems you hesitate to find SD for the job.
How do you plan to do panic stop while bleeding the brakes?
Bite the bullet and stop being road hazard.

ep4

You can brake hard on an empty road, or in a parking lot, without endangering anyone. Once the bubble is pushed out, assuming there is one, you can then bleed the brakes. I didn't plan on lying under the car while it was being driven, to crack the bleeders while someone slammed on the brakes.
I plan to pressure bleed the brakes again to see if the pedal feels better. If that does not make any difference, then I may take it in and have it bled. As I stated earlier, the car stops well, I just feel the pedal should be higher/firmer.
I didn't notice an answer to my question above. Should the pedal be pumped until firm, before pressure bleeding?

kajtek1

You don't pump the pedal during pressure bleeding.