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Discussion Starter #1
Hi Guys I was driving my 560sel 1991 model around 120kph a week ago after the ABS LIGHT has been on for a while when I applied the brakes to my surprise the pedal won't move at all it's kind of scarry as if the whole pedal was frozen.

But after trying a couple of times more it finally released and allow me to brake the car.

I brought the car to a mechanic immediately and he told me that I need to change 3 ABS sensors (do I need 3?) but since they didn't have the parts he just clean the sensors and the LIGHT ABS on the dash was gone.

I was able to use the car without any problems then today again without the LIGHT ABS on the dash I encountered the same problem as usual I was travelling at 120kph then the car won't allow me to step on the brakes but after a few try it work again.

Can you guys advice me what to do? Is there a way to turn OFF the ABS until I find the parts needed.

It's as if my car's ABS sensors is sending a meassage to the ABS unit not to allow me to press on the pedal to avoid skidding but the car is running at 120kph.

Has anyone here encountered the same problem?

Is this really a ABS sensor problem???
 

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1990 SEC
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That's scary. :eek:

I would have thought that the default setting for the ABS system if it malfunctions would be simply "OFF", i.e brakes would work as if there was not ABS circuit and you'd be able to lock the wheel if you stomped on the pedal hard enough.
 

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2005 W220 S500 4Matic / 2008 W211 E350 4Matic
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AxelWulff said:
I would have thought that the default setting for the ABS system if it malfunctions would be simply "OFF"
It is. This sounds like something far worse; if the sensors are dirty and causing false ABS firing, the light would not be on, as the problem would be that the system was operating under the assumption that it was in tune and functioning properly. The light on the dash means the system is non-functional. This sounds like a brake problem unrelated to the ABS which has become serious enough to disable the ABS system. This car should not be driven until the issue has been solved by a professional.
 

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Discussion Starter #4
300se126 said:
It is. This sounds like something far worse; if the sensors are dirty and causing false ABS firing, the light would not be on, as the problem would be that the system was operating under the assumption that it was in tune and functioning properly. The light on the dash means the system is non-functional. This sounds like a brake problem unrelated to the ABS which has become serious enough to disable the ABS system. This car should not be driven until the issue has been solved by a professional.
The car has bnew set of rotors all 4, new pads, brake sensors and newly changed repair kits for the calipers.

The ABS sensors was cleaned recently (it was very dirty) after the first incident since no parts was available.

Is there a way to disable the ABS to prevent it from firing?? Is there a fuse that turns OFF the ABS?

I had two mechanics look at it and both says that I need to change 3 ABS sensors 2 in front and 1 in the differential.

Wasn't the ABS supposed to FIRE stop and go (PULSE) instead of just preventing the pedal from depressing completely.

Can someone here help me get the part number for this 3 ABS sensors needed my VIN is 1260391A375209 thanks
 

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1982 280 se aut. ecc. - sold
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I'd look at your mastercilinder and do a good flush!

gr J
 

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just fyi, it takes quite a bit of pressure to lock the brakes... you get used to living without ABS. =]
 

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Agreed, the master cylinder or vacuum sytem may be at fault, and a flush and bleed of the entire system is in order. The ABS will not prevent brake use. Nothing should prevent brake use. If you must disconnect the ABS, you can do so by undoing the main wiring harness from the ABS computer. This can be done by depressing the metal clip on the left side of the box and pulling up on the side of the harness that the wires exit the plug from. The ABS computer is inside the false bulkhead, almost directly in the center of the car from left to right.
 

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Discussion Starter #8
ok thanks for the reply guys I will ask the mechanic to do a flush of the whole system just to make sure and if problem persist then I will try to disable the ABS.
 

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1982 280 se aut. ecc. - sold
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Don't forget the mastercilinder!!

gr J
 

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Discussion Starter #10
a3jeroen said:
Don't forget the mastercilinder!!

gr J
What do you mean by the master cylinder?

Won't flusing the system just bleeding every brake until the new fluid runs to the bleeder?
 

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He means don't forget to have your mechanic inspect the vacuum actuator and master cylinder for faults, and be prepared to purchase replacements for one or both.
 

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If you still want to diable the ABS, open the cover on the ABS unit (in the engine compartment) and remove the silver colored relay. This will disable it and turn the ABS light on. However, I don't think that will give you temporary relief, as it sounds like a master cylinder problem. Once ABS is diabled, your brakes will work normally, without "locking" or "pulsing".
 

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300se126 said:
He means don't forget to have your mechanic inspect the vacuum actuator and master cylinder for faults, and be prepared to purchase replacements for one or both.
Thanks that was exactly what I meant!

gr J
 

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Discussion Starter #14
Since the last incident the car's brakes runs fine at the moment.

If this is a cylinder or master vacuum problem won't I encounter it on a regular basis.

The car's brake dosen't freeze anymore and is normal at the moment but I'm scheduling it for a flush and use DOT 4 instead of DOT 3 is this ok? The shop told me that DOT 4 would have higher boiling point.

As per the mechanic who want's me to change the ABS sensors. He told me that the old wires on the sensors are damage and was just splice on together again by the previous mechanic so he recommends to get new ones plus the first time we had this problem was when the ABS was lighted (which means not working ).

But I will ask them to check on both as well.

Previously when my brake freeze there was no pulsing it was just that the brake pedal won't go down but after a few try it release and work normally.

Could this be contributed by DOT3 and DOT4 being mix up at the same time???? I just recalled before this problem we had our rotors and pads changed by another shop and back then they dismantle the caliper kits but just put back the old caliper kits since no repair kits was found in all the stores here then after a few weeks the repair kit arrived and I had a different shop change the caliper kits.

Prior to this change of rotor, pads and caliper kits we never encounter our brake freezing up.
 

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OK (sigh), if your ABS sensors are old... change'em. I (we?) don't think they are causing your freeze up. Maybe during the pad-change the calliper was pushed back in that the piston in your master cilinder, that's the thing directly beneath the reservoir traveled to a position wher there was rust or contamination and now the rubbers inside are damaged. Other possible scenario: coincidentally the vacuum line to your brakebooster or the membrane in the booster is damaged at precisely the time that your brakes were done.
Not nagging, but get it fixed right. Bad brakes cause big accidents!

gr J
 

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Discussion Starter #16
I think if the brake booster membrane is damage I would have experience that brake pedal would kept on going down to the floor when I depressed it steadily specially during traffic.

It could be a bad cylinder but I'm wondering how come it doesn't act up regularly and the time interval is weeks before one freezing happens. I think it's only the cylinder that is capable of freezing the brake pedal or the ABS pulsing (but it supposed to pulse not steady freezing it)

My concern is two mechanics already told me that it's the ABS sensors that I need to replace and they don't see anything wrong with the cylinder or the brake booster.
 

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I think if the brake booster membrane is damage I would have experience that brake pedal would kept on going down to the floor when I depressed it steadily specially during traffic.
Not necessarily. That would be "no pedal" from a defecitive master cylinder. That's when the master cylinder is not compressing the brake fluid, and you get a "squishy" pedal that does not stop the car.

When reading your post, I got the impression that your pedal was locked solid, and that sounds like you lost power boost (and were feeling the full effor needed to brake the car). It takes a *lot* of effort to apply the brakes without the power booster.

There are few things that would cause a problem like that. I would suspect either a booster problem, or possibly a binding in the master cylinder (as stated previously).
 

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I think we may all be missing a critical point here. We need to know if the pedal resistance occurs with the ABS light on on not. If the lamp is not lit, then the problem very well could be sensors - IF the brakes simply produce SOME resistance, while the ABS pump is firing, that could very well be a sensor issue. Many people mistake the initial resistance of the ABS pump priming for a panic stop for pedal lockout. One needs to be very familiar with their car's ABS system before they can know for sure. Personally, I know for a fact that the ABS pump, if priming for a panic stop with the brakes not depressed, has a tendency to provide some resistance upon initial application of the pedal, yet when the pedal is pushed further it will apply ABS braking. Getting past the initial point of resistance feels like stepping on a light bulb; small resistance at first, then a rush to the floor as the bulb breaks - or the pump allows harder braking.

If the pedal truly is frozen, something else is to blame. If your sensors are dirty or bad, you will either have ABS firing all the time at low speeds, or the light will always be on and you will have no ABS. The only problem that spliced wiring could produce would be loss of communication with the computer due to different gauge wiring interrupting the sensitivity of the units. Again, this would produce one of the two aforementioned issues. If you are certain that your problem is pedal lockout, and that you do not hear the ABS pump priming while the pedal is locked, you should not drive your car until you get the thing looked at by a MB specialist. It is very improtant that you trust issues this serious only to somone who knows these cars well. A good indy shop will do, or the dealer if you feel like pissing your money away, but don't just go to somone who doesn't specialize in MB products or even just European cars. Some Jiffy Lube kid will probably be too confused by the fact that you don't have drum brakes in the rear to accurately diagnose your issue.
 

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Discussion Starter #19
mhamilton said:
Not necessarily. That would be "no pedal" from a defecitive master cylinder. That's when the master cylinder is not compressing the brake fluid, and you get a "squishy" pedal that does not stop the car.

When reading your post, I got the impression that your pedal was locked solid, and that sounds like you lost power boost (and were feeling the full effor needed to brake the car). It takes a *lot* of effort to apply the brakes without the power booster.

There are few things that would cause a problem like that. I would suspect either a booster problem, or possibly a binding in the master cylinder (as stated previously).
The brake pedal was LOCKED SOLID and It took some hard pressing before the LOCK was release and brakes works fine "normal"

Some guys also told me it could be a leaky check-valve.
 

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rebel_mtc said:
The brake pedal was LOCKED SOLID and It took some hard pressing before the LOCK was release and brakes works fine "normal"

Some guys also told me it could be a leaky check-valve.
Sounds like no vacuum assist to me also.
 
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