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  #1  
Old 12-07-2003, 01:55 PM
daveCT's Avatar
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ABS locking up

hello

I have a stored 16v for a few Mo. now ..and took it for a spin
before the storm , and the oddest thing happened,

I had zero brakes, the petal was so hard and I could feel the ABS clicking, I disconnected the front 2 sensors and the brakes worked fine, and when i hook the back up , they worked fine again, then before i was ready to park it they seized agian , super scary,
This is the first problem i ever had with the Mercedes ABS like this.


Isn't when there is a malfuntion the ABS should just be bypassed, why on earth would it lock up and have NO brakes,
..
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  #2  
Old 12-08-2003, 12:04 AM
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Location: Evansville, Indiana
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Stuck front pistons/floating caliper or bad brake hoses?

Bad booster?

ABS will default simple (ie as it it weren't there), not rock hard and no brakes. It's a servo system that releases the fluid pressure, then re-applies it, no way to give a very hard pedal.

Peter
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  #3  
Old 12-09-2003, 03:57 AM
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Hello daveCT,

Psfred is only right in the first part of his explanation.
ABS will default simple indeed but with a "normal" failure.
The symptoms you are discribing are NOT normal.
Indeed, ABS releases pressure in the brake of the slipping wheel.
But where does that pressure go you think ?
Not into the brakefluid reservoir but into the master brake cylinder.
Why ? To keep your brakepedal HARD ! Otherwise you would feel the pressure releas AND you would compensate it by pushing harder on the pedal !
And as the pressure release is rapidly pulsing, you get that odd feeling in your right foot as a warning that there is an intervention of your ABS and thus your car is loosing "grip".
So your problem looks very scary to me ! I never opened up an ABS so you'll
need a rebuild or a new one. Most certainly not cheap at MB's stealership !

Danny
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  #4  
Old 12-09-2003, 08:18 PM
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ABS releases the pressure in the brake line by using a solenoid servo and some check valves. The fluid goes into the servo, then is pushed back into the brake lines when pressure is restored. Obviously, this make the pedal vibrate.

If you are on wet ice, you get some noise from the wheels and brake pads, too.

ABS has been around for a long time now, always fails "simple" as if it wasn't there. It is designed to leave normal brakes when it fails, not to lock things up, for obvious reason.

Poineered by Chrysler in 1978, I think.

Rock hard pedal sounds more like a failed booster or broken line to me -- makes the brakes very hard. Or stuck calipers -- the ABS will attempt to match wheel speeds, so if one wheel has brakes and the other doesn't, you can lock up a tire and the ABS will work. Very hard pedal, as one or two pistons aren't moving the in caliper.

Get the brakes checked, front and rear. I suspect a mechanical problem, not an ABS problem.

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!
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  #5  
Old 12-10-2003, 11:07 AM
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WELL that can be a ABS problem! IF the system thinks that the sensors have UN-equal speeds the pump will pulse the brake & feel like NO-brakes. THIS happens only at low speeds like 5MPH or lower!! Good luck.
There was even a service bulletin back in 1989-90 on that problem. MOST of the time it is cracked OR broken wires in the front sensors.
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  #6  
Old 12-10-2003, 05:05 PM
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As the car has been in storage, check the tyre pressures. That can cause different rolling radii which confuses the ABS, although it normally just shuts down and brings up the warning light.
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  #7  
Old 12-10-2003, 05:30 PM
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yup it only happens @ very slow speeds, and totally pumps up
the petal with no brakes, i just put new 17in AMG momo's on it ?
but done think that would matter, Plus the fluid is pretty dark
and the power slots have made the brake dust very caked up around the sensors, Plus they are unplugged and back in the barn and i will have to tune up/clean brakes this spring.
thanks
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  #8  
Old 12-10-2003, 06:47 PM
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Same thing happened on my 190E 2.6, and it was the front ABS sensors. Replacing them fixed the problem. The sensors would read that one wheel was locked and release pressure to that caliper. That gave the feeling like the brakes were failing. If it goes away when you disconnect the sensors, then my money is on the sensors themselves. I tried the same diagnostic test, and had the same results.

Not sure about the sensor price for the 16V, but years ago I bought my sensors from the dealer for about $500CDN for the pair.
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