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Marty, Mercedes Technician
Category: Mercedes
Satisfied Customers: 53979
Experience:  Bosch Certified Master Tech. Over 35 years experience.
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1983 Mercedes 380 SL. Has been sitting for a couple of

Customer Question

1983 Mercedes 380 SL. Has been sitting for a couple of years. No brakes at all. I replaced master cylinder. Went to bleed brakes and after pumping brakes like forever no fluid came out of line at right rear brake. Took an air hose and blew into one of the main lines I took off at the master cylinder. Fluid came out OK. What could be wrong? Master cylinder? Booster?
Submitted: 10 months ago.
Category: Mercedes
Expert:  Marty replied 10 months ago.

Hi Ray, it's not unusual for you to not get the back part of the master cylinder reservoir filled with fluid. Double check the fluid level first. Fill the reservoir all the way to the brim and then open the rear bleeder and see fluid eventually drips from the bleeder. It may take awhile before it starts dripping. If you don't get any fluid try loosening the master cylinder at the booster and pull it away from the booster then see if it starts dripping. Let me know what happens.

Customer: replied 10 months ago.
OK, the reservoir was full, we did get a drip, but that was it and that took forever. Wore my leg out pumping...The fluid would want to drip but for each pump it would get sucked backwards into the line. What exactly forces the fluid into the line? Is there a rod or something in the booster that creates the vacuum into the line? Just wondering....Reason why I ask because the pedal goes all the way to the floor as if there is no resistance at all.
Expert:  Marty replied 10 months ago.

When you let go of the pedal the master cylinder will suck in air if you leave the bleeder open. Only open one bleeder at a time. Start at the right rear. Connect a rubber hose to the bleeder and route it into a clear bottle of brake fluid. Keep the end of the hose submerged in the fluid while a helper slowly pumps the brake pedal. Pump until no more air bubbles come from the hose then have your helper hold the pedal to the floor while you close the bleeder. Repeat the procedure at the other 3 wheels. left rear, right front, left front.

Customer: replied 10 months ago.
We did all of that. We've done this plenty of times but it was this one that is giving us issues. I have an '88 IROC we did before jumping to the Mercedes. Only difference is that I replaced the booster on it. Being 28 years old, I wanted to insure the entire braking system was in perfect working order. We did all of what you said, it just would not drain but only barely dripped...barely. Like I said, I pumped the brake pedal until I was tired of pumping with 0 results.
Expert:  Marty replied 10 months ago.

Do you get fluid from all of the other bleeders?

Customer: replied 10 months ago.
No, we stopped after we did not get any from the right rear and after I had to use air to get any flow at all. Knew that wasn't a good sign. Wanted to find out what the problem could be. I figured if we didn't get anything from the far point, we wouldn't get anything from the rest. The reservoir remained full the whole time we tried the first bleed. Pedal went to the floor while pumping. 0 resistance.
Expert:  Marty replied 10 months ago.

Try going right to the master cylinder and open the lines and see if you get fluid from the master when you push the pedal down. If you don't get fluid try loosening the master from the booster so there is about 1/4" clearance between the master and the booster and try it again.

Expert:  Marty replied 10 months ago.

If the rod in the booster is not letting the cylinder come all the way back it won't draw any fluid from the reservoir.

Customer: replied 10 months ago.
Is there an adjustment for this rod?
Expert:  Marty replied 10 months ago.

Not really, sometimes you can screw it in but it is usually a fixed rod. If loosening the master allows fluid to flow to the calipers I suspect that you may have the wrong master cylinder installed.

Customer: replied 10 months ago.
I can't get to work on it until this weekend. In the meantime, have a great Thanksgiving and I will let you know what happens on Monday.
Expert:  Marty replied 10 months ago.

Sounds good Ray. Have a Happy Thanksgiving.