Brake Bleeding Blues

[greasewagen]

Rear brakes on my 1986 190D not functioning.
air was introduced into rear brake line when caliper was dissasembled. Put back together and tried brake pumping method. At first little dirty fluid came out.
Now nothing comes out, air or fluid. Tried using vaccum pump bleeder but couldn't pull anything out of the bleeder valve.
It seems as if there is a closed valve dividing the front and rear brake circuits.
The front part of master cylinder reservoir is full to max, but the rear smaller chamber doesn't seem to fill up with fluid.
I will try to fill up the rear reservoir and bleed again. Any ideas on what else to try? Previous posts seem to mention master cylinder as a possibility. Not sure how to test it though.

Ken

[Kestas]

First, do you know if the master cylinder ever went dry during the job? Second, you may want to try gravity bleeding, where you simply leave the bleeder screw open and let gravity rough bleed the brakes. I think it takes no more than a few minutes.

There is a possibility that the rear brake hose has internally disintegrated... but I don't see how that could affect both rear brakes.

Beyond that, I too remember reading about losing half the brakes when something goes wrong with the master cylinder internals.

[speedy300Dturbo]

The rear of the reservoir ONLY fills up as the front half overflows - so basically you have to add lots of fluid to the front half so it spills over the dividing "wall" into the rear half!

[2300com]

If the fluid was pretty dirty, you may have a clogged reservoir and the fluid cannot get to the rear chamber fast enough. I went through the same process and problems recently as well.

I ended up doing two things. I replaced the reservoir with a new one. Mine had crud in it that I think was making fluid run to the second chamber too slowly. You need to siphon out the current fluid and then it pulls off rather easily. The reservoir is just snapped in to some rubber grommets, no other connectors holding it in place.

Second, I bought Speed Bleeders. I replaced the stock bleeder valves with these. They have an internal pressure valve that does not let air up the line, only fluid out them. Makes it easy to do the bleeding yourself.

Good Luck-

[glenmore]

The simplest thing to check is make sure there is fluid in the rear chamber. If you are parked nose down, you'll have to fill the front chamber almost to overflowing before fluid makes it back to the rear chamber. Try it parked on a flat surface. Wipe up any spills on painted surfaces immediately.

glenmore
1991 300CE

[greasewagen]

thanks everyone for the help. the rear chamber of the master cylinder had in fact gone dry. I filled it all the way to start. installed speedbleeders on rear calipers. I used a vacuum pump to get the dark crudy fluid moving. At the end I had clean fluid with no bubbles coming out. Took for a test drive and felt 110% better! My mistake was letting reservoir rear compartment go dry.
now for my next hurdle, a rear bearing!

Ken

[omegabenz]

With the Motive Pressure Bleeder you dont have to worry about the back part of the reservoir going dry. You can read up on this by searching my name. Although you are finished, you may want to buy this bleeder anyway, it works very nicely for the money.

Have fun with the rear wheel bearing, Id have someone do it, its a pain.

[2300com]

I have the motive pressure bleeder and agree it is great. However, if your old fluid was pretty bad (like mine was) the reservoir can get clogged so the pressure from the bleeder still won't be enough without replacing or cleaning the reservoir.

The pressure bleeder does make the job ALOT easier though.

[autozen]

Ken,

Congrats on solving your problem with th help of people on this forum. I suggest sticking with the gravity bleed that you have done. It has worked for me for over 30 years, and the rules of gravity have not changed.

Peter