Last week I went to change my rear sway bar links and noticed my rear pads were getting real low. Luckily I had a set of pads and decided I might as well take the time and replace them. Unfortunatley I did not have the time to bleed the lines, but I figured I'd order the front pads (which I knew were also getting low and starting to squeel a little bit) and do it once I replaced them. Well, I replaced the front pads today with no problems. After changing them I decided I should bleed the lines as well. I set up my brake bleeder and went to open the RR bleed screw and for the life of me no fluid came out. I scratched my head a bit and went back to the resevoir only to find fluid overflowing everywhere out of one of the spouts where the sensor connects to (not sure what it's called). Thoroughly angered I cleaned up the mess and popped off the rubber cap, covered it in duct tape and tightened that with a rubber band folded over numerous...simply so I could get pressure and return to bleeding the lines. I pumped it up to 20 PSI and even though it held pressure neither one of the rear bleed screws had fluid coming out once loosened. The front ones bled just fine. I'm at a loss here. Is my line clogged or my caliper gunked up? How would I be able to troubleshoot this ( I guess crack one of the brake lines leading to the caliper?)? ...And do I need a new brake fluid resevoir?

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1983 300SD White with Grey interior

Crack one of the bleeder screws on the rear calipers and get into the vehicle and press the brake pedal. See if you get fluid out of the caliper when you do this.

If so, then try your bleeding process again.

You may need to repeat with the opposite rear caliper.

you didn't have it at 20psi initially, did you? 5psi should be about the max.

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1985 300D cali 190K

http://mercedes.thatchermathias.com/mw300d.jpg

Why don't you try bleeding the old fashioned way ?
Have someone sit in the drivers seat and slowly pump the brake pedal and hold.
You crack the bleeder AND retighten it.... then call to the person and say " OK" and they pump and HOLD again...
Perhaps your system would not allow the fluid to flow to the caliper for some reason. This other method may show if that was the case...
Of course, the person in the vehicle must monitor the fluid in the master cylinder so that no air can be put into it due to the fluid level being allowed to get too low.
I have seen some amazingly gunked up caliper pistons over the years.. so that is possible.... but some type of normal systemic non flow condition seems best to check first in your case.

I did pump the brakes with the bleed screw open and nothing came out. I also compressed the caliper and with that some fluid squirted out, but then pumped the brakes and the piston wouldnt re-compress. Yet I checked it this morning after driving and theyre fully compressed now. It's driving me nuts. I think the next time I head to the Junkyard I'm gonna pick up a full set of calipers and rebuild them.

Also...what do you guys think about my resevoir leaking like that?

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1983 300SD White with Grey interior

I had the exact same trouble with my pressure bleeder. The brake fluid oozed from every opening in the resevior. I finally removed the 2 black rubber caps, replaced them with 1/2 ID plastic hose with clamps on both ends. Then the cap leaked, I added a 2nd cap gasket and used teflon tape on the cap threads. I was pumping to about 16PSI. Success. The bleeder got most of the air out, I employed an assistant to pump the brakes, which removed the rest of the bubbles. In retrospect, the main advantage of the bleeder is that it has a large capacity of fluid, so you don't run dry during bleeding.

Perhaps you did this but just did not type it out in the post...

You know that this is a one way function to work properly ? If you just pumped your brakes with the bleed screw open it drew in air at that time ( in addition to whatever was in there already )...
For others , if you did it correctly, you must pump, hold pressure on brake, open bleeder screw, close bleed screw, release brake pedal , pump again, open bleed screw, then release pedal from floor or however low it went... and keep checking fluid reserve in master cylinder so as to not introduce air from the top...

Same thing happened to me, there was so much gunk in the bottom of reservoir I could not bleed the brakes till I got pissed off enough remove the reservoir and clean it with detergent. Guess the PO didn't believe in PM, it was horrible in there.

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Cheers,
Robert