Brake bleeding problem! - PeachParts Mercedes-Benz Forum

rwthomas1 · #1 12-06-2002, 08:47 PM

Well, the brakes in my 84'300D WERE working fine but for some reason the rubber grommets that seal the fluid reservior to the master cylinder had become really soft and were leaking brake fluid. I picked up new grommets and dot4 fluid, changed them out and proceeded to bleed the system starting from the wheel farthest from the master and working from there. Here is where it gets wierd. I can bleed the two rear brakes and get a decent pedal but when I bleed the fronts the pedal goes soft, right to the floor! I have tried vacuum bleeding and with a helper and the best I can get is a mediocre pedal and this is bleeding the rears last..... The car is driveable and I can lock 'em up but it ain't anywhere near what it was. The pedal was very firm when I started, what am I missing? I have bled many brake and hydraulic clutch systems and have never had this kind of trouble. Any help would be appreciated. Thanks, RT

jbaj007 · #2 12-07-2002, 12:24 AM

There are two chambers on the reservoir. Sounds like you're not filled into the forward chamber (there's a "dam" separating front from rear chambers). Make sure brake fluid is always in both when bleeding or you suck air into the front lines. FWIW

speedy300Dturbo · #3 12-07-2002, 12:58 AM

yeah, you'll need to fill it up REAL full so that the chamber overflows into the next.

#4 12-07-2002, 09:51 AM

With BOTH chambers of the m/c reservoir full do a two man bleed starting while the engine is RUNNING. I have had problems with some of my cars by trying to bleed without power, the late 123's are on this list.

I would personally NOT try bleeding with the vacuum bleeder. Either use the method above or a pressure bleeder, you can get one for less than $50.

Good luck,

rwthomas1 · #5 12-07-2002, 10:13 AM

Thanks for the tips. I figured out the reservior issue early on and always kept it full. I will try to bleed with the engine running and see if it makes a difference. Thanks, RT

rwthomas1 · #6 12-07-2002, 03:46 PM

Success!!! It worked! Bleeding the brakes with the engine running did the trick. I just bled the fronts and all is well. I don't have any idea why it works that way but I am happy now. Kinda makes 2-person bleeding tough when you have to yell over the diesel racket. Thanks again, RT

Stevo · #7 12-07-2002, 07:04 PM

I don't get it . Whats the deal with the engine running??

gota admit, I'da never thought of that one.

#8 12-08-2002, 09:49 AM

Okay, I'm ready! Someone will label me as a Sexist after my explanation.

Usually when we look for an assistant for bleeding brakes, it is our wives, girlfriends or kids. They probably have the strength, but don't understand the word EFFORT. They don't press very hard on the pedal.

By starting the engine, you now have the brake booster applying the needed EFFORT.

Some vehicles are not very difficult to overcome the resistance of the brake booster with the engine off. Others seem to have too much resistance from the booster, and that 95 pound lady just can't or won't overcome it.

Okay, so I'm a Sexist, arrest me!

Stevo · #9 12-08-2002, 11:45 AM

I knew it, Larry Bible is a sexist,

... get the kids Ma, were outa here.

PS .....thanks Larry. I get it now. I bought one of those Speedy Bleeders and did my 5 spd 240D the other day, what a piece of cake.

Ken300D · #10 12-08-2002, 12:24 PM

The Power Bleeder device that uses air pressure (from its own self-contained pump) is the greatest thing for bleeding and flushing brake systems.

All those years of suffering through "press-and-release"......

I pity the fool who tries to flush their brake system without one. Well, actually, you just have more patience than I do. With the Power Bleeder, you just put a couple liters in, screw on the cap, pressurize - and then visit the four bleeder screws.

Very nice.

Ken300D

JHZR2 · #11 01-22-2004, 09:41 AM

I was just looking through the archives, and came up wth this post... I do have one question about it though... In another post, I believe by DieselHead, essentially what happened was using a power bleeder, fluid would leak out of the two caps on the top of the reservoir that are the attachments for the brake fluid level sensor.

Has anyone noticed this problem, and have a possible solution?

Thanks,

JMH

Stevo · #12 01-22-2004, 10:44 AM

"Has anyone noticed this problem, and have a possible solution?"

Sure, you have to replace those rubber "caps" sometimes, they are cheap but the effort is well worth it as the pressure bleeder makes it SOOO easy to bleed the system.

JHZR2 · #13 01-22-2004, 11:34 AM

OK, thats simple enough... I wasnt sure f they were integral to the sensors there or what... Plus, it seems that 15psi on any rubber cap like that ought to help it blow out.

I havent tried pressue belleding this car, but look forward to doing it soon, as the reservoir gromets need replacing anyway.

Thanks,

JMH

Stevo · #14 01-22-2004, 12:10 PM

" integral to the sensors "

Ya, I know what you mean, dont want too go yarding on things that you not sure about. I have had a history of destroying parts

Those caps take a bit of effort to remove.