Brake Master Cylinder Question - PeachParts Mercedes-Benz Forum

RML · #1 11-30-2009, 08:23 AM

On my 84 300D I put on new front discs, new front pads and new rear pads. I did not have any braking problems before, other than having worn through a brake pad sensor on the front. I flushed the line with "Valvoline Synthetic DOT3 and DOT4" brake fluid. The stuff that come out was the color of honey, so it had not been done in a while. I have had the car for about three years now and 9K miles. Bled the brakes all around starting from the RR and working forward until the fluid came out clear with no bubbles. Took it for a test drive and now the pedal goes nearly to the floor. The car stops but the pedal did not travel that far before. I tried to pump it up, but that does not make a difference. I checked the reservoir and it is full and clear with new fluid.

Could I have damaged the master cylinder seals by having the brake pedal travel further during the flushing and bleeding process than it had been in years? That is, did the seals get scored in a rough area of the master cylinder bore that they had not visited in years?

BTW, I also put on a new ball joint and repacked the front wheel bearings, but I think that is unrelated.

Thanks for any input.

Brian Carlton · #2 11-30-2009, 08:52 AM

Did the rear chamber of the m/c ever run out of fluid during the bleeding process?

RML · #3 11-30-2009, 09:10 AM

Quote:

Originally Posted by Brian Carlton

Did the rear chamber of the m/c ever run out of fluid during the bleeding process?

Quite possibly. There was one point when I got some air coming through the line. I did not think the reservoir was that low but went up and topped it off. It is possible that the rear chamber emptied but I did not notice it because I was looking at the front chamber.

Brian Carlton · #4 11-30-2009, 09:19 AM

Quote:

Originally Posted by RML

Quite possibly. There was one point when I got some air coming through the line. I did not think the reservoir was that low but went up and topped it off. It is possible that the rear chamber emptied but I did not notice it because I was looking at the front chamber.

I'm in the same situation with the SD. It's really difficult to get the air out of the system. I procured the metric master cylinder bleeding kit from NAPA and bled the master back into itself. Then, I bled the fronts again. Brakes are acceptable, but still not right. I'm going to try to bleed the rears again and see if I can get some improvement.

Pedal travel is about 1" too great.

In your case, the entire rear system is full of air and you're going to need to start from scratch.

I also don't think much of the use of the m/c to provide the bleed capability. I use a pressure bleeder.............cheap............."EZbleed"..............and it saves the work and risk on the m/c.

JHZR2 · #5 11-30-2009, 09:29 AM

+1

you have air in there, and the easiest thing to do is get a pressure bleeder.

Somtimes you do need to use the pedal, even with a pressure system, and Ive been lucky - no issues.

Wodnek · #6 11-30-2009, 10:17 AM

I have never been successfull bleeding a 123 by the pumping the pedal method or using a mighty vac.

On summit racing dot com you can get a pressure bleeder with the BMW / Mercedes adapter for about $65. It works great. Or for just over $100 you get the adapters for just about everything.

It is a well made unit made in USA.
I like the ATE blue fluid due to its ease of being able to tell when its bled through completely.

RML · #7 11-30-2009, 12:00 PM

This info is all really helpful. I am going to go on the "air in the system" theory for now and try bleeding again. I flushed and bled my '85 300D with no problems so was encouraged that all would go well. I guess I didn't watch that rear chamber closely enough. I'll check out the power bleeders and report back.

RML · #8 11-30-2009, 12:25 PM

I was just reading about the Motive Products Power Bleeder. It is listed as the successor to the EZBleed which they say is no longer made. I am curious, if you screw on an adapter cap to the reservoir and feed in pressurized brake fluid, when you take off the adapter cap, is the fluid in the reservoir sitting at the very top of the neck? Do you then bleed some more off with the pedal to get it down to the "max" line? You obviously do not want to have brake fluid spilling out into the engine bay. I read that this stuff is highly corrosive.

toomany MBZ · #9 11-30-2009, 12:31 PM

Once you're done and release pressure the excess flows back into the bleeder, those things are a big help, I didn't need as much pressure as suggested. You shouldn't have any overflow issues.

Brian Carlton · #10 11-30-2009, 12:32 PM

Quote:

Originally Posted by RML

I am curious, if you screw on an adapter cap to the reservoir and feed in pressurized brake fluid, when you take off the adapter cap, is the fluid in the reservoir sitting at the very top of the neck? Do you then bleed some more off with the pedal to get it down to the "max" line?

Yes, it's filled right to the top of the cap.

I generally let a bit out of one of the wheels to lower it down out of the neck. I don't believe the "max" line is anything to be concerned with.

RML · #11 11-30-2009, 01:47 PM

Ordered the Motive Products Power Bleeder. $49.95 plus shipping. I decided not to play around with the pedal method any longer. If nothing else, it will save me alot of time, spilled fluid, air in the line, aggravation, waiting for a helper to be free, yada, yada. I checked on the parts and tools sections of this site first but did not see it. Seems like it would be a good seller.

It should be in Friday, in time to bleed the brakes this coming weekend.

Stevo · #12 11-30-2009, 04:01 PM

The pressure bleeder was one of the best investments that I have made in tools for these cars.

Makes bleeding a piece of cake

RML · #13 12-12-2009, 10:44 PM

Used my new pressure bleeder today. Worked like a charm. There was air in the right rear line. The pedal feels firm now and engages near the top of the travel range. I am doing some other maintenance items so haven't road tested it yet, but expect the problem has been solved. Thanks for all of the help and suggestions.

P.E.Haiges · #14 12-13-2009, 12:17 AM

I've found that "gravity" bleeding works for me. The fluid just runs thru the brake lines and the bubbles come out.

P E H