I have a 1986 Mercedes 300SDL with brake problems! I was took it out for a drive smelled something burning. Tried to stop - pedel goes right to the floor no brakes. The parking brake works though. Any ideas what is wrong. Someone told me the ABS compressor could be gone and it costs 2700.00. Would that smell like it's burning before it goes. It was not a real strong smell but it was there. Any ideas would be appreciated.

 

even without abs the brakes should still work. you loss pressure in the brake system and or there is not enough fluid getting to the brake calipers. When you press the pedal, it causes the fluid to move through the system and the abs uses the fluid pressure to basically prvent the brakes from locking up (reason for the pulsating and odd noises when you slam on them.) could be master cylinder and yes sometimes they give smell of burnt brake fluid or very very burnt brake pads or sometimes there is little to no smell.

That ABS system is not a cheap buy and it was very advanced for it's day. If you on budget, you might still be able to find good ones in junk yards as that ABS compressor is usually a pretty hardy piece and besides the rubber bushings and connectors usually last long time.

But I would check the master cylinder first as usually even when the ABS system stops working in that car, (amber ABS dash light), the brakes work yet a bit touchy and will lock, like just about any 1970s era car, but if the master cylinder goes, you can forget about it as far as brakes are concerned. Wont be any.

 

oh and you can pick up a master cylinder for a hundred or two.

 

thanks for the input .... i just bought the car from a guy and i think it was sitting for almost 2 years ... becuz no record of registration since 2008 .... car is actually in pretty nice shape .. 167K miles, barely any rust ... i decided to change the usual things, oil & fuel & tranny filter .... i was amazed to see almost no metal filings in the tranny pan with that mieage .. ...wooooooow ... i put full synthetic 5 w 40 oil in .. to be nice to the old girl .... i cleaned it up ... mostly from sitting , dust and leaves etc.. when i was driving it home the pedal felt soft but worked ... ( but all of a sudden nothing @ all ) almost rear ended somehome .. scared the heck out of me ...good thing i was only going about 15 miles per hour ... but park brake works fine ... wouldn't that mean the brakes are still " functional " to a degree .... in otherwords not worn out so badly ..nothing left to stop with ...? and from outside this strong smell of what i try to describe as kinda like burning brakes like you smell from big rigs going down a steep hill ???? but couldn't put my finger on it ... i put the car on ramps and checked it out underneath and can't see any leaks or anything, brake resevoir is full .... havn't had had a chance to take tires off yet ( no time ) when i felt the rotors from the backside the rotors seemed " allright" not all scored and grooved just a slight ridge , no squeaking or grinding, no lights on dash ....

so you think it could be the master cylinder .. .but what could account for that smell .... a ceased rotor/ pad ???

 

i fixed the problem, it was the master cylinder was leaking worn out persay.... and since it hadn't been driven for a couple years ( parked i think ) one brake was ceased too ... fixed it .... brakes are still a little spongy tho....

everyone keeps talking about how zippy these cars are but mine is a dog, gutless any ideas what to look for ...?

I changed all the fluids, oil, tranny, and diff replacing with premium full synthetic oil, and of course all new filters

it starts great, even @ 0 degrees it start practically on first turn of starter, no blowby to speak of and no smoke while idling and practically no smoke when first started cold ... go figure ...

 

a w126 sitting for longs periods of time tend o develop lots of leaks. some people get lucky and get away wit ha few. Mine sitting in a box for a winter and 6 months had a relatively new water pump internal gasket go, and a few minor rubber seals around some accesories (luckily no hydromatic problems or leaks.)


Sometimes when changing the fluid of that ABS system you can get away with a standard bleeding if it's a routine one but lots of time after storage you have to really do the whole nine bleeding by the book to get the brake feel back and of course the correct fluid level

 

what do you mean by the "whole nine yards" ..... you mean .. bleed the abs too ...if so how you do that ...i assumed the air would be bled out of it @ the same time ??? i had someone pump the brakes while i bleed each wheel until the fluid ran fee of air as much as i could ..... but brakes work " alright" but still a bit spongy ..... imo .... doesn't seem to be leaking anywhere cuz don''t have to add any for quite a while now ... same level ????

 

what i mean is that the ABS system is very sensitive to moisture that can build up over time. You know routine brake fluid changes usually not enough moisture have built up to affect anything so a normal bleed is good.

Sometimes, in an ABS system air remains trap inside the ABS unit and that's where the words of "special tools and machines" come into play in the repair and maintanance book. If you do a standard brake bleed as muc has you can and the brakes still feel a little spongythen there might be some still trapped inside the ABS unit that can be removed by finding a shop with the actual ABS bleeder machine. Most brake shops have one.
90% of the time a normal bleed job should work as the Bosch ABS system usually is flushed and bled with rest of brake system. IF this car is a diesel I doubt it has ASR so that is one less thing.

Usually spongy brake feel is air in the line.

Is brake performance degrades after use aka when the the fluid gets warm? (brake fluid works in environments that is above boiling point) Or the pedal seems to go lower and lower to floor and o stopping the car takes longer?

 

I am also having break problems, my breaks are going to the floor but not all the time. I am not leaking fluid, changed rotors and pads and am at a loss any suggestions.??

 

And it too is A 1986 300SDL