What happened to my brakes????? help - PeachParts Mercedes-Benz Forum

crashone · #1 04-15-2007, 09:16 PM

Well I rebuilt all 4 calipers, changed the rubber hoses, drained the MC, filled it back up ( both sections) and started vac treatment since it is only me. I got plenty of fluid to come through (so it seems) out of of all four calipers but I have no brakes, nothing, nada. I started bleeding last night about 10:30pm and finally quit at 1:30am. Today after work I bled them some more (about 1.5 hrs) until the storms came back. I did take it for a slide around the neigborhood here (that was interesting) to see if pressure would build and stay or if there were any leaks. No leaks still no brakes. I have pumped about 2qts through the system. Sorry this is long, any ideas? Thanks

TheDon · #2 04-15-2007, 09:33 PM

no leaks so air must be getting into the system more or less.

JimSmith · #3 04-15-2007, 10:10 PM

No brakes means you are not making differential pressure with the master cylinder. If the system was dirty from no brake fluid changes, it is feasible the cylinder has a raised metal at the "traditional end of travel" of the master cylinder piston from normal actuation of the brakes. If you pushed the pedal to the floor, you may have torn the rubber seals and now they can't sustain the necessary differential pressure to make the brakes work.

I can't think of much else that could cause your problem. Maybe someone else with more experience with these systems can pipe up and offer a few more options.

Good luck, Jim

Wodnek · #4 04-15-2007, 11:18 PM

I have a 78 300 D with the same issue. I just decided one day to replace the 4 rubber hoses going to the calipers. Then I cahnged the brake fluid by pulling it thrugh with a mitey vac until it was clear. In the end almost no brakes. You have to stand on them and the car will barely slow. I replace the master cylinder, no change. I bled another 2 quarts through, still no change. I was told that a mighty vac doesnt have enough suction to pull the air bubbles through. I haven't proven it one way or the other yet. I will have to work on it again in the comming months.

#5 04-15-2007, 11:21 PM

Try gravity bleeding the brakes using a hose on each bleeder nipple going into a clean soda bottle of brake fluid. Let it bleed for a few hours, while keeping an eye on the fuild level on the master cyl. Open all four nipples at once, and let gravity and time do the work.

Knightrider966 · #6 04-16-2007, 12:14 AM

You need a buddy to help you with this! There is no way one person can blled all the air out successfully without a pressure bleeder. Your buddy will have to pump the brake pedal 5 times and hold it to the floor on the 5th push and hold it down hard. Then you open the blled screw at the closest caliper to the MC, drivers side, then go to front passenger's side, then to drivers side rear, and last to passenger's side rear open the bleed screw while your buddy holds the pedal down hard and fluid should squirt out with some bubbles spurting out too. Repeat this procedure until you have pedal firmness back. Try it and let us know what happens!

crashone · #7 04-16-2007, 08:49 PM

Thanks for the replies. I had a friend stop in and we bled them for awhile, him pumping peddle me turning wrenches. We got some air bubbles out but then all fluid at all four corners. We could get pressure but then the peddle would drop to the floor. Now I need to do some research and see about bad Master Cylinders etc. Seems strange that it would let go like that. If any one has any ideas please post. Thanks for the help. So close but so far away.

#8 04-16-2007, 09:17 PM

Sounds like you have a bad master cyl., they usually fail when they are marginal and someone bleeds the brakes using the master cyl. The extra travel when bleeding the brakes will compromise the weak seals.

crashone · #9 04-16-2007, 09:36 PM

That's what I was afraid of. Oh well when you go fast it is a good thing to be able to stop fast.