I've been worried about my brakes not having the power they should. My old TD could lock up all four any time I asked it to. My 240D won't come anywhere near that, even with both feet pushing all my weight into it. To see how bad they really are, I did a 60-0 panic stop test:

Total distance- 460ft.
Tire lockup- No
Rotor temps- front 320*f, rear 125*f. (45*f outside air temp)

The front brakes were smoking (literally) when I took their temperatures. The pedal feels good. No sponginess, or vibrations.

When I flushed all four brakes during the engine swap, they all spit fluid like normal. Fluid used was Valvoline SynPower Synthetic Brake Fluid.

The brakes are fine around town, but I feel they will lead me to grizzly accident if I ever really need to stop on a dime.

EDIT 2008: Turned out to be air in the rear brake lines. Bleeding the brakes solved the problem.

460 feet is very very horrible... the spec is 165 feet. The power booster on my 300D doesn't put out nearly as much boost as it should... when putting my foot on the brake pedal and then starting the engine, the pedal doesn't go down any. But it puts some boost out, I just can't do two hard stops in a row with vacuum assist. Nevertheless, the brakes lock up if I want them to (generally not a good thing to do). The reason the booster is crap is because the seal between it and the master cylinder deteriorated after 20 years and when I replaced the master cylinder, the booster had an inch of brake fluid in it. Before I replaced it the brakes were always kinda weak... though not really mushy and would never lock up... but afterwards... they feel very nice and stop very easily with minimal foot pressure when you see that red light comin up. I would change your master cylinder even if your pedal isn't mushy, it improved my braking immensely...check your pads too for glazing.

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1985 CA 300D Turbo , 213K mi

Somthing is wrong with your brake system. That 60-0 distance is not good. I am replacing the master cylinder on my 300SD and going with Goodyear SS brake lines for added insurance. It is good that you replaced your brake fluid. That is often neglected in all cars. I like to change the brake fluid yearly in our cars. In my Ford mustang with upgraded brakes I was very pleased with the improved braking after we installed aftermarket braided stainless steel brake lines, and a better booster with a brand new m/c. For our new to us 1983 300SD a new master cylinder and these brake lines should be relatively cheap insurarance. I am just hoping the brake booster is OK. That bad boy part is over $400 for our car.http://www.performanceproducts4benz.com/productpage.aspx?pid=105836&name=Goodridge+G-Stop+Stainless+Steel+Brake+Lines
You also want a very good quality brake fluid with a high boiling point like what you are using. Good luck. I will let the experts rip apart my ideas now. John

Take a little time to read all the threads you can find in the archives on poor brakes. Although basically the brake system looks really simple on the 123 series cars they do seem to have a few oddities. I have a 77 300d that the brakes do not seem quite as good as they should be. Another spring project and not quite certain what will turn up. We only know the brakes can be pretty good on 123s and should be. Forget the 400.00 booster. Even if you need one a unit off a salvage vehicle should check out ok. Yes of course they fail but not all that common to eliminate the possibility of using a good used one in my opinion. If that turns out to be the problem or for some reason you have to check out by substitution that it is perhaps the problem.

sounds like a booster issue. Maybe it either has a leak between the Master cylinder and the booster ( a simple O ring seal) or you may have had the M/C slowly leaking brake fluid into it over a long period. I have had that happen and it will reduce braking capacity.

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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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Section 609 MVAC Certified
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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

If the car is not stopping in the proper distance, yet the pads are smoking hot - my Internet diagnosis is you have incorrect pads on the car. Yes, they probably fit correctly but I'm saying they are made of the wrong material.

Internet diagnoses are free and have just about that much value.

Ken300D

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1982 300D at 351K miles
1984 300SD at 217K miles
1987 300D at 370K miles