1985 300 SD. The brakes have always been excellant. Last week I would have to push the pedal half way down and push again to get a firm pedal.It does not always do it,sometimes the pedal will only go down a little like it should. I pulled all wheels the brakes look good. I am thinking if it was a vacuum problem the pedal would be hard to push.I am starting to think it maybe the master cylinder. That would explain why sometimes they work good and sometimes they do not. Has anyone else seen this problem..thanks

sounds like air has entered the system somehow. when was the last time any brake work was done or the last time the fluid was changed? its possible it could be the master cylinder but i would try bleeding/ changing the brake fluid first.

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mc full up?

tom w

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

have not done any work on the brakes since getting the car--over 1 1/2 years ago. MC is full.

Sinks intermittantly, but pumps up on the second stroke?

Seals shot in the MC, time for a rebuild or replace. Sometimes hard to get a kit, MC isn't expensive.

Sooner or later they won't pump back up....

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

Tell me exactly how you determined the m/c was full.

The W126 is notorious for running it's rear reservoir out of fluid.......and you cannot tell if you look from the driver's side.

Just looked at the side of the mc to see if it had fuild in it---what am i missing?

Lean over the fender and look at the m/c from the passenger side. The two reservoir levels should be instantly visible. The rear reservoir is about 1/4 the size of the forward reservoir. They are not visible from the driver side.

Thanks -I will look tomorrow.

Pulled a m/c off of one of my 2 parts 300sd. Put it on my car,bleed it out and brakes all better.Can you get a rebuild kit-so I can rebuild the one I took off? thanks

Dave - before running off to the parts store for MC or Boosters. Observe the two rear brake line going to each wheel while someone applies the brakes (motor running). Look for swelling in the brake lines.

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I changed the m/c and brakes are good.Do you think i still might have a problem?