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  #1  
Old 02-05-2006, 03:02 AM
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Default Brake grinding

Hello,

2000 E430 RWD. I'm having a terrible time diagnosing a front brake grinding. It's coming from either side on the front. I've replaced pads and rotors but at a certain speed(10 - 15 mph) while applying the brake, there is a grind with every rotation of the wheel. It is not prominent when turning so I don't think it's a wheel bearing. It goes a way under acceleration as the pads separate from the rotor.

WHAT IS ROOT CAUSE!!!! HELP!!!

Thanks, Matt

P.S. The K&N air filter makes a signifcant noticeable improvement on acceleration. Haven't had the chance to evaluate top cruising speed!
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  #2  
Old 02-05-2006, 04:35 AM
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Default RE: Brake grinding

Hi,
Difficult to tell without hearing the noise.
However if it goes once the pads are retracted it is quite possible that the caliper pistons are beginning to seize.
Did you check for free operation when the pads and rotors were changed.
Are you sure the rotor water spash guard is not rubbing due to having been bent at pad / rotor replacement time.
Stuart
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  #3  
Old 02-05-2006, 12:08 PM
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Default RE: Brake grinding

Stuart,

I know the splash guard is not rubbing. It's behaving exactly like a warped rotor. Two mechanics were positive it was a warped rotor but now I've replaced them and still have the problem.

What is the procedure to check for free operation of the caliper piston???

Thanks, Matt
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  #4  
Old 02-05-2006, 12:41 PM
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Default RE: Brake grinding

Stuart,

If the calipers are seizing is it just a matter of replacing the caliper seals and cleaning up the caliper surface?

Matt
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  #5  
Old 02-05-2006, 02:30 PM
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Default RE: Brake grinding

Hi Matt,
Quite straightforward.
With the car safely jacked up and the wheel off etc rotate the brake rotor. If the rotor is warpped it will touch the pads once every revolution. The "warping" is known as "runout". A SMALL amount is acceptable and normal.
If run out is noticeable you need to check how much there is with a dial gauge or similar. Need to get acceptable limits from workshop manual. SleepWalker will advise I'm sure.
New rotors should be fine as long as you ensured the mating surfaces didn't have any burrs or damage on them and that the asembly was put together ensuring no dirt between the mating surfaces etc.
In normal use the small amount of runout knocks the disc pads back and thus stops the rubbing noise. However if the pads are knocked back too far due to excessive runout the brake pedal will have long travel on it when you come to stop.
If the caliper pistons are partially seized the brushing action of the runout will be insufficient to knock the pads back and the noise will continue.
If the pistons are partially seized you may get away with stripping the caliper and removing corrosion with fine emery cloth etc but this is a job for someone who knows what they are doing and what is OK and what is NOT. If the pistons are badly seized then new calipers (expensive) will be required. Seized calipers will off course significantly reduce stopping ability.
Only work on the braking system if you are competent and confident to do so.
Let me know how you get on.
Stuart.

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  #6  
Old 02-05-2006, 02:45 PM
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Default RE: Brake grinding

The pads brush the rotor and retract so I think the piston is OK. I don't have excessive brake pedal travel so I don't think run out is too bad. Especially with brand new rotors.

I did all this on the front because I can feel the rubbing(grind) through the steering wheel. Is it possible that the rear rotors are the problem which can be felt through the steering wheel?

This point might help diagnose: I originally turned the rotors and replaced pads with EBC "Green Stuff" organic pads. The problem improved significantly but still remained. Next I replaced the rotors and it got even better but not perfect. I put the original pads back on with 1/2 pad life left and the problem improved again but still remaines slightly(enough but bug the **** out of me!). To summarize, now the configuration is new rotors with 1/2 used OEM pads. I haven't touched the rear. What does this tell you anything???

Thanks, Matt
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  #7  
Old 02-05-2006, 05:13 PM
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Default RE: Brake grinding

Hi Matt,

Sorry but I didn't read your original post carefully enough.
"...... certain speed(10 - 15 mph) while applying the brake,"

Might be a good moment for me to go and hide!

OK its speed dependent and is modified when you changed pads and rotos. I wonder whether its brake temp sensitive?

As an observation new pads are shaped so as only to permit a proportion of the pad to contact the disc. They are sort of wedge shaped. As the pads bed in they gradually adopt 100% contact area. Since your pads are 50% worn this special shape will no longer be apparent. If the noise really bugs you you could try a new set of OE pads.
Special pads are notorious for intro all sorts of noise under various conditions. Performance is always a compromise between stopping power, wet resistance etc. and NOISE.

An alternative approach would be to chamfer the edges of the worn OE pads somewhat in order to enable them to bedin properly. Suggest you have a look at a new set of OE pads and either purchase or replica shape.

Sorry about previous misinformation..

Stuart
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  #8  
Old 02-05-2006, 05:21 PM
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Default RE: Brake grinding

Stuart,

Thanks much for sticking with me to resolve this one. I'm going to try and chamfer the pads. I'm a trying to keep cost down to make this car economically feasible. I'll try like crazy to fix it myself first.....without spending more money!

Thanks, Matt
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  #9  
Old 02-06-2006, 03:49 AM
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Default RE: Brake grinding

Matt,

I must have been half asleep yesterday.

Something else I note is that you do not mention shims and grease in your post.

MB OE pads have a shim clipped to the back of the pad that has an area of coating on it. In addition the pads should be fitted in a manner where this shim is greased with special very viscous heat resistant grease. This grease should come with a new set of pads. If not it is an associated parts.

Possibly the coated area and the grease discourage noise generation between the pad and caliper piston surfaces.

WARNING: TAKE CARE THAT THE CORRECT GREASE IS USED AND THAT IT IS APPLIED ONLY IN THE MB RECOMMENDED AREA WELL AWAY FROM THE ROTOR AND PAD FRICTION SURFACES!
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  #10  
Old 02-06-2006, 10:50 PM
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Default RE: Brake grinding

Stuart,

I think the shim and grease are to eliminate high frequency vibration in the pads during braking. The high frequency produces high pitch squeeling.

Check this out. I chamfered both pads quite a bit. Down to about 1/2 surface area. Now the grinding seems to be independent of brake application! Going about 30 - 40 mph and letting the car roll to a stop without brakes applied will produce the sound/vibration. Start accelerating again and the noise will fade away only to return when decelerating. The problem is relatively equal if braking or not. Grinding might be too harsh of a term.

Turning does not induce the noise so I don't think it's wheel bearings. Could it be the tires???? When I rotated the tires I noticed the tires on the back were spinning in the wrong direction. The tires are directional. Those back tires are now on the front and spinning in the right direction. However, the noise has existed since I purchased the car at which time the front tires were originally spinning in the correct direction.

Is it wheels or bearings....or still something in the brakes???

This one is challenging. Thanks, Matt
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Old 02-06-2006, 10:50 PM
 
 
 
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benz, brake, brakes, braking, car, constant, dont, front, grind, grinding, makes, mercedes, neutral, pads, revolution, rotate, turning, wheel


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