I'm having a brake issue with my '85 300td. Occasionally, when braking I will get resistance for the first 1 1/2 and then the peddle travels all the way to the floor board before I get any more resistance. This is not a consistent problem. The break fluid, pads, etc. look fine. Any advice?

The brake went to the floor on my 240d two months ago and the brake booster and master cylinder had to be replaced. Fixed it right up. Took it to Midas and they did the work for $650.

replace your master cylinder before the object that stops your car is the one in front of you.

Its not that hard nor expensive to do it yourself and bleed the brakes afterwards.

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Proud owner of ....
1971 280SE W108
1979 300SD W116
1983 300D W123
1975 Ironhead Sportster chopper
1987 GMC 3/4 ton 4X4 Diesel
1989 Honda Civic (Heavily modified)
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"He who fights with monsters might take care lest he thereby become a monster. And if you gaze for long into an abyss, the abyss gazes also into you." - Friedrich Nietzsche

I had a similar problem but mine turned out to be a bad caliper leaking lots of fluid. My petal went to the floor. But when you added fluid, it stayed up.

Yours sounds like the master cylinder. You can do that yourself.
I would also consider the repair kits for the calipers so you dont have leaks in them.

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1982 300SD Light Blue
2002 Honda Accord SE
1974 Toro Wheel Horse Tractor
2000 Toyota Tundra Pickup

My 240D had the same problem, brake pedal would go to the floor. it says in the owners manual to bleed the brakes every spring, they sure needed to be bleed, i got nothing but air for a long time, after that, my brakes were GREAT!!

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1983 Euro 240D 277K
2016 Mazda 6
Coming Soon, 2013 Mercedes E350 Bluetec
Formers:
2012- Mazda 3
2007 Outlander- complete pile
1995 E300 Diesel 208K
2007 VW Passat 2.0T 63K SOLD
2003 Jaguar X-type 3.0 Sport Sold 04/11 w/88K
2009 Lexus RX350 9061 miles. Sold 04/09
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certain that your mc is bad. that is how they fail.

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.

tooling down I76 in heavy traffic on the outskirts of philly, had a couple of abrupt stops in the rush hour traffic, someone pulls into my lane, I step on the brakes... NADA!... right to the floor, I panic-pump and the pedal come back in time, but is still super soft.

I figger my brake fluid must be low (clutch MC used to leak but stopped some time ago) I pull onto the shoulder (let it idle) pop the hood and the brake fluid is just fine... hmmm, I look under the car and all calipers and hoses are fine... hmmm.

Hop back in and carefully nurse it to the park, pumping the brakes like a... well you get the idea. Shut her down and take the dog for a walk. half hour later come back, fire her up and voila... brakes!! They work fine... not even a hint of softness.

Conclusion: Air in the lines. I'm gonna start by bleeding them, I'll report back.

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Cheers,
Robert

Bled the brakes... well 75% of them. I broke off the bleeder valve on the RR caliper

The was minimal air in the lines, but the brake fluid was very funky looking... I bled into a clean bottle, and the fluid was brownish and looked like it had water in it. The pedal is firmer now, I'm pretty sure that the old fluid had enough water in it to boil after some heavy braking.

Thanks to all who have shared their experiences b4 me.

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Cheers,
Robert

It is much more likely that the seals in the master cylinder are failing. It takes more than a few hard stops to boil the fluid; more like a trip down a mountain.

In this case, bleeding will fix it temporarily, but the problem will come back.

It can be heat related, affecting you most when the underhood temperature is higher.

Don't play games with your brakes. You very likely need to rebuild or replace your master cylinder. If it were my car, I would not drive it.

Replace the master cylinder. I had some squishy brakes that I bled, and that made them firm up a bit but the braking performance was less than acceptable. Changed the master cylinder and took it for a spin and locked all the wheels up cause i was so used to stomping on the crappy feeling brake pedal. Night and day difference.

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1985 CA 300D Turbo , 213K mi

also be sure your mc is full.

it is easy to have the back part of the mc be low and not notice.

but sounds like a purge of system is a good idea as a min if that is found to be the case (low).

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.