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Discussion Starter #1
Hi all, I was driving my 1982 300td today. I noticed that the brake pedal seemed softer than usual. When I pulled over there was a burning smell and some smoke from the front drivers wheel area.

any ideas? How do I trouble shoot this? What do I look for?

I'm pretty far from a Mbz mechanic, so I'm trying to figure this out, and/ or at least make it safe to drive to the mechanic if possible.

Thanks in advance for help and advice. :)
 

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'01-E320 & 02-ST2
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Hi, Rich.

If you can safely raise and support the car, start with the right front wheel and get under and look. If you have a brake fluid leak you'll notice it, just follow the hose back from where it connects to the caliper. It should look old and dusty and dry, if it's cracked it will be wet. Be sure to inspect the connection to the brake line and the line itself, as the lines can corrode out, too.

Note: If they are OE hoses they are probably all just time bombs, so if that's the issue I'd be sure to change them all. And if the brake pedal is feeling funny, I would not risk driving the car. Call up one of the roadside programs so you can get it towed free, then once you're "covered" call them up and tell them it broke down conveniently at your house, then have it towed, assuming you don't want to do the work yourself.

Good luck.
 

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1985 Euro 300TD Turbo, 1983 Euro 300TD turbo, 1979 Euro 240TD and 1981 300D converted to euro.
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still in the sf area?
 

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'01-E320 & 02-ST2
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Sounds more like a sticky caliper to me...? :)
That's a possibility, good idea. Rich, any pulling or anything from that side?

Still, it's not that tough to raise it and safely support it and check for leaks. If none are seen, then it's probably safe to drive to a shop, particularly if the pedal feels normal again for the first couple of stops. The sticking caliper could cause brake fade, which could result in a soft-feeling pedal.
 

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1985 300D Turbo
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589 Posts
ok.. i'm having the same problem and this is what i've come up with. Some of this is theory but figure it might help you chase things down...

It might be your lines. When they swell, they allow you to activate the brakes, but the tension is not allowed to release cuz the swelling of the lines don't allow the fluid to travel back towards the reservoir... Furthermore, the heat that is created effectively heats the brake fluid ("boiling over") heating up and creating pressure in the lines. As you continue to drive and the pressure builds up..the calipers continue to clamp down. Are you losing acceleration?

I'm still investigating whether or not it is the lines or the caliper is stuck or maybe even the mastercylinder. I'm hoping if I fix my lines and flush the fluid and maybe change the pads/rotors I should be ok. However there is a strong chance that the caliper might need to be rebuilt.

If you have this similar problem, you might want to look at repacking your wheel bearings as well.

I think the spongy feeling is the air as your press the brake. If all was well, it would be nice and stiff because of the brake fluid.
 

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83' 300d
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Brakes are conceptually simple and easy to work on.

First off, check your brake fluid. If you're low, that can indicate leakage or pads that are worn down. Check Codes is giving ya good advice.
Raise and support your car. Try spinning the wheel. When the brakes are not being stepped on, the front wheels should spin freely. Inspect the hoses for leaks. Check the brake pad thickness.

If ya can ever get DieselKraut22 to show up, he's great to learn Benz stuff from.
 

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1984 300D
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If you think it is sticky Calipers:
Jack the Car up have someone step hard on the brakes and release them. Turn the Wheels if you feel a drag and espspecially if the drag does not go away your Calipers are sticking.
Calipers can stick due to the Pads and Rotors being too thin for the Pistons to retract properly.
The Seal insinde of the Caliper can be hardend and unableto retract the Piston.
Rust and muck inside of the Caliper can keep the Piston From Retractiong.

Step on the Brake Pedal and go out and loosen the Brake Line Fitting at the Master Cylinder; if Fluid Spurts out under pressure it could be a problem of the Master Cylinder not allowing the Fluid to retun. Also when the pressure is relieved there the Wheel will free up.

If no spurting happend in the above test but your Brakes still Drag again have someone step hard on the Brakes. This time loosen the Brake Bleeder Screw. If Fluid spruts out under pressure and the Wheel frees up you have a problem with the Brake Hose holding back the pressure.

If it is neither of the above problems it is a problem in the Calipers themselves.

A lot of Mercedes parts are expensive but new Brake Hoses are pretty inexpensive and good insurance.
 

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Discussion Starter #9
Thanks everyone for the answers and advice. I'll do some work and see what I can find. Also, I drove the car today and it was fine, so I think that supports the "sticky caliper" diagnosis.
 

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5 Speed "85" Euro TD , 5 speed "85" Euro 240D, "79" 5 spd 240D, 5 spd "94" Dodge/Cummins PU
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To check if its a sticking caliper, hop out after driving for a while (when the car comes to a complete stop:rolleyes:) and feel the wheel, it will be hot if the caliper has been sticking.
 

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1983 300D
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27 Posts
"I've just taken the 300D to my workshop for the same problem; rear left-hand caliper appears to have sprung a leak. Good thing I nipped it in the bud."

UPDATE: Below are some quick snaps of the perished seals from both rear calipers; these seals, which were factory originals going back to 1983, were so hard and brittle, that massive brake fluid leakage was an inevitability. Pads were also saturated with brake fluid and were replaced accordingly. Calipers were also spray-painted gloss black prior to refitting.
 

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1983 300D Turbo
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question: why would thin break pads cause the brake fluid to disappear?
someone suggested this. I really do not know but would like to know.
 

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'79 240D, 83 300D
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Well, it could cause the level to be lower in the reservoir as more fluid is in the caliper when the pads are thinner. It would be a gradual thing. But it takes a leak somewhere to make it disappear.
 

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1979 240D
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i agree this is something you can do by yourself... i would be looking at bleeding each caliper to see which one gives you high resistance.... take the brake pads out(which will be hard to do if the caliper is staying closed) then when you go to push the cylinders back into the caliper it should be easy little to no effort... if you have to pry the hell out of the cylinder to get it to bleed the caliper is bad... had the issue with my 450sel went to a junker pulled a caliper and back to normal... i wouldnt drive it to a mechanic i wouldnt drive it anywhere.... you could warp rotors... dry your bearings out and end up doing more damage depending on how far you have to drive...
 
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