new rotors, 20K on pads, new MC, flush = weak braking now - PeachParts Mercedes-Benz Forum

spugeddy · #1 02-23-2008, 08:34 AM

In the last two days my brakes went from good, to almost not working.

New pads about 20K ago, new rotors about 2k ago (pads looked good), did MC change about 10 K ago, with brake fluid flush...

The feel is loose, but not limp like when the MC went out... it holds the pressure without sinking, but not as stiff as a few days ago. Also when I turn the engine off, they get real stiff....pumping doesn't do anything....the brakes aren't sticking, or shaking, just real weak grab, and more pedal travel than a week ago...

I am going to look at it this am and suspect air in the lines, right.... For a cheap route, I may just check the resovoir, and bleed it all the way to rule that out....

Any other things to be looking for

engatwork · #2 02-23-2008, 08:36 AM

My first thought is air in the system. Has it been doing it since the work was done or did it just start doing it?

spugeddy · #3 02-23-2008, 08:49 AM

just started out of the blue. work was done long ago... drive 70 miles a day no symptons until this week.

engatwork · #4 02-23-2008, 09:24 AM

Can you see any leakage at the wheels?

DAR2KMR2 · #5 02-23-2008, 10:45 AM

Check the brake hoses. I had a similar thing happen to me a few years ago and it was a bad break hose. If you find one moist or bulged then I would replace the pair (front or rear).

David Roseman
Long Beach, Ca

Robert Squires · #6 02-23-2008, 11:50 AM

* A set of brake hydraulic hoses on a high mileage car is a great idea. Hoses usually get overlooked. A hose aneurism will cause a soft pedal (and a dangerous condition). That condition just isn't that common. I've also seen a hose look ok on the outside and start breaking down on the inside, causing some really wierd braking symptoms.
* What was the issue with the old master cylinder? Was it leaking fluid out the cylinder? Did you check (with the mc removed) for fluid inside the booster?
* Did you manage to crack or disconnect the vacuum supply source to the booster (w/o realizing it) while you were working on the master cylinder?

mobetta · #7 02-23-2008, 12:31 PM

new sealing O ring on the MC/Booster contact surface??

or maybe the "new"(reman??) MC is leaking? how's fluid level??

Hatterasguy · #8 02-23-2008, 03:03 PM

Sounds like a leak or a bad hose. I'd change all the hoses since they are cheap and probably shot, then flush the system really well. While your doing it look for leaks.

spugeddy · #9 02-23-2008, 05:30 PM

the resevoir was bone dry for the rear chamber...

I refilled, but think I have air in there. It is better but not good....

I guess the rear pads are low????? I haven't been checking the brake fluid for awhile, shame on me, air probably got in there right?

I will test drive around the subdivision, and maybe do the two man brake bleeding... can I do that with just the rear?

Passenger rear first, then drivers rear....

I don't have issue with the MC anymore. It was leaking air..(worn out) bought a new one (not used, or reman) and that fixed the dead pedal....

toomany MBZ · #10 02-23-2008, 05:33 PM

Quote:

Originally Posted by mobetta

new sealing O ring on the MC/Booster contact surface??

Yes, check the booster itself if you cannot determine where the leak is.

lutzTD · #11 02-23-2008, 06:27 PM

Quote:

Originally Posted by spugeddy

the resevoir was bone dry for the rear chamber...

I refilled, but think I have air in there. It is better but not good....

I guess the rear pads are low????? I haven't been checking the brake fluid for awhile, shame on me, air probably got in there right?

I will test drive around the subdivision, and maybe do the two man brake bleeding... can I do that with just the rear?

Passenger rear first, then drivers rear....

I don't have issue with the MC anymore. It was leaking air..(worn out) bought a new one (not used, or reman) and that fixed the dead pedal....

did you bleed the master after running the rear dry? Also you should have gotten a warning light with the low fluid, did you plug in the fluid sensors? As for bleeding, the $5 one man bleeders do work if you cant find a buddy to pump the pedal. The best bleedr ive used is the Groits Garage vacuum bleeder. man that thing works good. I can flush a whole system in 20 minutes with that thing

spugeddy · #12 02-23-2008, 06:33 PM

just to recap...

MC is fine. It is brand new with less than a year on it... I did bench bleed it, and the system worked great for months... WIthin the last two days I had lost brake feel and stopping power. Checked today and rear resovoir was dry, front side was fine...

I bought some syn Dot3/Dot 4 fluid at Mall-Mart, and am considering brake bleeding the rears cause of possible air in the system now since the resevoir was dry..

THanks all for the input. I posted last night when it was dark out and I had to wait for sunrise to see the fluid level was low...

Hatterasguy · #13 02-23-2008, 07:41 PM

Well their is your problem, check all the lines you probably have a leak somewhere.

mobetta · #14 02-23-2008, 07:58 PM

If it was totally empty, you have a leak.

Robert Squires · #15 02-23-2008, 08:04 PM

* I've only used DOT4 in my shop for years. ATE SL or Pentosin are reliable choices. Forget about anything else, DOT3 or DOT5.
* When bleeding/flushing the hydraulic system (this is pre ABS and SBC), start at the caliper farthest away from the master cylinder and work in. That is, begin at the right rear, then the left rear, then the right front, and finally the left front. That should work all the air out. I don't like the pressure or vacuum assisted bleeding tools. A simple plastic bottle, a silicone hose to the bleed screw (get some BMW silicone vacuum hose), and a hanger is all you need. Just make sure that the hose is immersed in some fluid in the bottle. Doesn't take two people; do it all by yourself. Maybe 20 pedal strokes per caliper, never letting a reservoir compartment go dry.
* There was a post that referred to an "air leak" in a master cylinder. Master cylinders don't leak air, just fluid. Were you talking about vacuum leak in the booster? Or something else?