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  #1  
Old 08-15-2002, 11:16 PM
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Question 93 300E Squeaky Brakes & ABS pulsates while coming to a stop

While driving slowly and applying brakes, the brakes may squeak. And when they squeak the ABS system pulsates at the exact moment the wheels stop. It sounds like springs are popping and the brake peddle obviously pulsates as well. This problem only happens when I'm experiencing a squeaky brake condition which is not all the time. But certainly happens almost everyday.

I have had my mechanic test drive it more than once. First he said it was the new rotors he had replaced, saying they were warped. So he replaced them again at no charge. That did not clear up the problem.

Next he said he thought the ABS sensors needed cleaning and this could cause a condition of this type. But in the end, it did not clear it up.

What could this be?

Peter
'93 300E 2.8
140,000
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  #2  
Old 08-16-2002, 09:11 AM
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yal yal is offline
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This may not be your problem but when the same thing happened to me it turned out that I had the wrong rotors on the car. Just before coming to a full stop the brakes would pulsate and squeek. Specifically the rotors were the wrong thickness. I had put a ventilated set on but the car specified a solid set.
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  #3  
Old 09-25-2002, 02:54 PM
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I have same problem

It appeared after I changed the outer wheel bearing of the front wheel on my sdl. The pulsating starts only on the drivers side when almost at a stop about 80% of the time.

I thought that the ABS sensor or the hub abs ribs were dirty, but cleaning did not help (much).

I then thought that I might have grease on the pads or rotors, so I am hoping that this will go away when the grease burns or gets mixed with brake dust and falls off.

Please post if you figure out what the cause is.

thanks
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  #4  
Old 09-25-2002, 03:55 PM
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Don't think this is the ABS, it cuts out below 3 or 5 mph, what you are experiencing is at lower than walking pace speed, right? Worse in Drive than coasting to a stop in Neutral?. Acid test is to disable the ABS (unplug the computer) and see if it still happens.

Both my Mercs have done this, it also seems to be worse in damp weather and I have put it down to a combination of cheap aftermarket pads and possible worn suspension bushes.

Any comment from the pros?
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  #5  
Old 09-25-2002, 05:20 PM
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only at really slow speeds

True it is only at way slower than walking speeds.

There is a decent ridge on the rotor, but the pads look fine- time for new rotors?
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  #6  
Old 11-09-2002, 05:44 PM
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The same thing is happening to me, I just got new front brake pads and now they squeal almost all the time when coming to a stop. They only squeal at low speeds, when I apply the brakes gently. They do not squeal if I apply the brakes hard. Then, while I'm coming to a stop with the brakes squealing, the brake pedal pulsates and goes closer to the floor. It seems like the abs kicking in, but I'm not sure.

Have you guys figured out how to cure this? Has the squealing gone away...cause damn it is loud and annoying as hell. I'm going to take it to my mechanic sometime in the next week or two. I'll let you know what he says.

Thanks,
Matt
94 E320
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  #7  
Old 11-10-2002, 08:04 AM
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The squeeking is because MB pads do not have anti squeal shims. You need to apply copper brake paste to the backs of the pads and where they contact the caliper. MB part No 001 989 10 51 or any good accessory shop.
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  #8  
Old 11-10-2002, 12:24 PM
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The activation of ABS at 0-6.2mph is always caused by sensor issues. Most commonly a specific sensor, sometimes a secondary condition busts the threshold for activation; such as fouled sensors or bad wheel bearings.

The only part that the squeeling contributes is the secondary activity (braking the threshold for activation). It is a very weak secondary activity and I would consider it a totally separate issue.

The ABS functions at all speeds but doesn't fault sensor activity below 10kph (6.2mph). The first place sensor problems occur is with the low speed activation usually in reverse while turning and passing over a vertical drop (like leaving my alignment lift - almost every car activates).

These low speed activations are usually just an anoyance. As they occur more often they will eventually wind up being observed at over 10kph which then sets the light and the problem then gets fixed (sometimes).
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  #9  
Old 11-11-2002, 01:42 PM
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I think Steve has hit the nail on the head again

This weekend, I changed my rotors (which were down to less than 0.9" - minimum is 1.0") and put in new pads also.

My former ABS pulsation on the drivers side at less that 10 mph is now happening at higher speeds. ABS now seems to engauge at any speed, as long as the braking force is moderate. Not much ABS pumping at higher speeds, but significant pulsing at lower speeds

Looks like time for a new ABS sensor.


If anyone has other ideas or knows how to test (by unplugging that sensor?), please let me know.

alec
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  #10  
Old 11-11-2002, 03:30 PM
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My mechanic (German guy, trained at the factory in Stuttgart, was Service Manager of the year in No. America in the 70s, - now runs his own shop) says that he ALWAYS replaces the ABS sensor when he replaces the brake pads. Cost is $6-7 each but cheap overall when accounting for the annoyance of some of what you guys have been experiencing.
I don't know whether or not this philosophy has helped us to avoid similar issues with our cars (neither of which are 126 models) but it certainly has kept brake issues out of our lives.
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  #11  
Old 11-11-2002, 03:41 PM
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Jay, either you or your German guy are confused. The sensors that he is replacing for 6 bucks are the wear indicating sensors. They have nothing to do with the ABS sensors which vary but all cost over 100 bucks a piece.

There is one at each front wheel and one on the differential for 3 channel systems and one at each wheel for the four channel systems with ASR.
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  #12  
Old 11-11-2002, 04:57 PM
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Dang it, brain still in 'weekend' mode

Steve B.,
You're certainly on the money (as usual). He replaces the wear sensors with each pad replacement, NOT the ABS sensors. I'm sorry to have provided mis-information.
To all on the board - this is the value of having professionals hanging out here to help us with our problems and concerns. As I just illustrated, mis-information can be easy to get but hard to live with (as well as expensive).
I wouldn't usually make a mistake like that, thanks for catching it Steve.
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1993 300 CE Cabriolet (A124) 131K miles
1997 C-280 133K miles

2000 BMW R1100RT 69K miles
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  #13  
Old 12-13-2002, 03:21 PM
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stevebfl,

Where exactly are the front wheel ABS sensors located?

My mechanic recently greased my front wheel bearings and I suspect that the sensors may have become fouled. I am more than happy to clean them myself, but I was unable to located them during a cursory inspection.
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  #14  
Old 12-13-2002, 04:05 PM
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Pronick

Our '91 300E had a distinct wobble when braking. At first I was suspecting the rotors, being thin, I replaced them. The pedal modulation stopped but not the shuddering in the steering wheel.

I then replaced a worn tire rod end and the it all stopped.

A friend did this also and still had problems. I suggested he look carefully at the pitman (idler arm bearings). They seemed bad, replaced them and was very pleased, but in the removal of the shuddering but also in the feeling of the steering being tightened up.

Haasman
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  #15  
Old 12-13-2002, 07:42 PM
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stevenstevensteven , look in your CD...

Barring that, the front wheel sensors have a cable running off the back of them through the wheel well to the engine compartment. On my car there are two cables per wheel - one for the brake pad wear sensor, the other is the ABS sensor.

If you want to clean the pickups that the sensor reads, I think that you will have to remove the hub/rotor, as the ribs that the sensor reads are on the engine side of the hub.

To clean the face of the sensor itself, you can either remove the hub/rotor or remove the sensor from the steering knuckle. While not hard, this is more than a 30 second job.

seeya around town...
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