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  #1  
Old 06-21-2002, 02:16 PM
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Brake squeal (when brakes are not applied)

One or both of the front wheels on my 1991 300D is/are making a squeaking sound that stops when the brakes are applied. I thought the problem may simply be brake dust, so I gave the discs a thorough spray with the hose. The problem did not stop. The wheels do not always squeak. I would say it happens about 75% of the time. The squeak always stops when I apply the brakes. Any suggestions?
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The MBs:
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1991 300D 2.5 Turbo - Sold at 221K
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  #2  
Old 06-21-2002, 10:42 PM
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My car did the same thing a while back. the disc itself was loose. I tightened it down and it stopped squeaking.

Alon
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  #3  
Old 06-22-2002, 12:32 AM
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Check your front brake pads. It could be the time for replacement.
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  #4  
Old 06-22-2002, 12:35 AM
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Alon, I remembered you told me to tighten the disc, but it doesnt really do anythign considering that you tighten your lug bolts down to 80 ft. lbs or more. Mercedes recomends 80, but I always do 90. It shouldnt do anything by tightening the disc, but I guess it does because it did work a little.

You may want to check the brake pads because they could have gotten cocked inside the brake pad bracket.

I have been fighting the same problem, but when you put on the brakes. Do they squeal when you are about to stop?

My car needs wheel bearings. Im going to do that this weekend, so Ill let you know if it fixes it.

Id try what alon suggests, then if that doesnt work. Let me find out if the wheel bearings fix it.

Since you will have the wheels off anyway, take off the calipers, and put antisieze on the edges of the pad and on the back maybe its binding / stuck on the pistons.


Austin
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  #5  
Old 06-22-2002, 11:26 AM
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Often a wheel bearing noise will go away when you brake. Usually, a wheel bearing noise will also go away when you turn in one direction or another at speed.

If only braking stops the noise, I would suspect the pads.
I will presume you already know they are not simply worn out.

This is typically a sign that the pads are not completely releasing for whatever reason.

I know MB prescribes some sort of grease paste for the backs of the pads, but I use the typical parts store 'anti-squeal' paste, which is more like a rubbery adhesive than a grease.
I first discovered that this goo was affective when I had a similar (but worse) problem on my 450SE (12 years ago), and have used it on many various cars with good results ever since. I would rate this one as the remedy "most likely to succeed".

After cleaning up with sandpaper, I apply a very thin coating of heavy Moly grease ('brake grease') to the caliper surfaces that the pads slide on. Of course, the W124 pads do have those nice metal 'shims' to slide on, so they are much less prone to sticking in this way.

Also, while you have it apart, check the caliper pins. If they freeze up, you could get the problem described. If the rubber boots have failed, the pins could be dirty/worn/corroded/stuck. The boots and pins are a cheap replacement part. These actually tend to hold up very well on the W124, but I have seen this problem on other cars. After cleaning, I use a silicone grease on the pins.

Lastly (and worstly), the piston itself could be binding. Folks rarely repair these themselves anymore, since rebuilt calipers are relatively cheap.

Best of luck...
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  #6  
Old 06-22-2002, 12:39 PM
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Lately my 400E has been doing this. Its a squeak coming from the left front wheel. When I turn right, it gets worse, when I turn left, it goes away. When I put the brakes on it goes away. I already cleaned the caliper and pads once, but apparently didnt work. Could it be a bad wheel bearing? I never seen a front one go bad before in these cars. How is the front wheel bearing set up on these? Is it a sealed unit like the back? Or is it like the W126's?

Thanks
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  #7  
Old 06-22-2002, 01:42 PM
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That is the 'classic' symptom of a bad bearing.
They will typically last "the life of the car" if repacked and resealed every 100k miles or so, but they will eventually wear out otherwise.

Collisions can cause premature failure (potholes, curbs, etc.), though the associated force required would usually bend an alloy wheel in the process, so a surprise failure is unlikely.

Not 100% sure of your model, but my bearings are conventional in every way- 2 tapered bearing sets with a seal at the rear.
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  #8  
Old 06-23-2002, 02:50 AM
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Thumbs up update

Just to update you guys on my problem, I took the pads out, cleaned the calipers, and lubed them up real good. I swapped pads from one side to the other on the caliper. So far the squealin has gone away (fingers crossed). I still dont know why it would go away on a left hand turn, and come back on a right hand one. Hmmm....
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  #9  
Old 06-24-2002, 01:06 AM
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Is the problem solved?
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  #10  
Old 06-24-2002, 01:01 PM
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Unhappy No it isnt

Well, Cleaning the pads and calipers only last about a day.

Now what should I do? It definetely made a difference for a little bit? Could it still be a bearing?
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  #11  
Old 06-24-2002, 02:48 PM
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I still vote for the bearings.
Since it does not appear to be the bearing itself that is making the actual noise, I would speculate that there is some excess play in the hub.
That is why is starts and stops depending upon which way you turn.
Check for play- could be an easy fix.
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