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  #1  
Old 04-17-2000, 08:02 PM
travis300D
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This old 300D has 4 wheel disk brakes and has started making a noise coming from both rear brakes. The noise is a metal grinding sound that varies in amplitude as the wheel turns and as pressure is applied. The tricky part is that the noise only occures if the car is in reverse. We have owned this car for over 20 years now and this is a totally new sound. I have tried switching from semi-metallic to carbon pads, and added brake shims but it did no good. On a side note, the pads are wearing evenly so i do not suspect a problem with the calipers; and the rotors are new. Thanks far any advice - i am really lost on this one!

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'76 300D
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  #2  
Old 04-17-2000, 08:05 PM
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Location: New Bedford, MA USA
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Check your parking brake shoes. A good clue is the noise occurs when backing up.

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Jeff L
1987 300e
1989 300e
1987 BMW 325
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  #3  
Old 04-17-2000, 08:07 PM
travis300D
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no brake shoes! This is a four wheel disk set-up. The pads are fine! Please try again thanks

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'76 300D
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  #4  
Old 04-17-2000, 08:46 PM
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Travis, I am not aware of a 4 wheel disc setup that uses the rear calipers for the parking brake. If you look where the parking brake cables enter the wheel backing plate, you should see an adjustment hole for the starwheel. If I am wrong, then I have learned something about older 300D's. Most MBZ's have 4 wheel disc setup. Most have little brake shoes inside the rear hubs for parking, emergency brake.

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Jeff L
1987 300e
1989 300e
1987 BMW 325
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  #5  
Old 04-17-2000, 09:40 PM
travis300D
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Maybe it is me who is learning here. Are these brake shoes in addition to the two that are part of the main braking assembly? I only know of the two main pads and had no idea that there were other shoes for the parking brake. Thanks - its time for me to sit down with my chilton's book. By the way, why wouldnt this be self adjusting?
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  #6  
Old 04-17-2000, 09:58 PM
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Location: New Bedford, MA USA
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Travis, Most of these braking systems have a separate mechanical emergency/parking brake system. These are very similar to regular drum type brakes, only much smaller. Not designed to do much more than park or emergency use. These tiny brake shoes are located in the rear rotors. If you look at the front rotors and compare what you see to the rear rotors, you will see the difference. The rears have a much bigger hub area. (AKA mini drum). the shoes themselves are about 1 1/2 inches wide. They do have a self adjuster, but most of the time this device, unless kept clean and lubricated, doesn't work very well. In some cases however, they can malfunction and over adjust the shoes so they are subjected to excessive wear. I believe this is what you are dealing with. The self adjusting feature works when backing up. It's too bad that owner's manuals don't give better info on this system. Unless your car has a rather different setup, you have little shoes that are probably worn out and scraping on the drums. How well does the emergency/parking brake work? Either it doesn't work at all or it's too tight. A little test for you. Put the car in drive on a level road surface with no traffic. Get it up to about 5-10 miles per put it in neutral and then apply the park/emergency brake. That should tell the story. Good luck.. BTW, another possibility. When backing up, your pads may be getting cocked out of alignment and rubbing on the edge of the rotors. Not likely but possible.

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Jeff L
1987 300e
1989 300e
1987 BMW 325

[This message has been edited by jeffsr (edited 04-17-2000).]
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  #7  
Old 04-18-2000, 12:57 AM
travis300D
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I dont know how to thank you. Your diagnosis is completely correct. This is my father's vehicle and hasnt gotten my attention since i was 18 yrs old and lived at home. I guess i have become too used to my american Z28 and forgotten what real automotive engineering is all about! The parking brake is doing almost nothing and i suspect those shose are far overdue for a change. In fact, i vaguely remember the e-brake was almost useless years ago when i used to drive the car. Thanks so much for your time and attention to my problem.
-travis
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  #8  
Old 04-18-2000, 10:26 AM
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You're welcome..

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Jeff L
1987 300e
1989 300e
1987 BMW 325
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  #9  
Old 04-18-2000, 02:51 PM
travis300D
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Well, I had hoped my problem would be so simple but i was totally off! Upon mre careful examination (parking brake is o/k), this noise is coming from under the car and is not directly related to the brakes! Although applying the brakes in reverse will cause the symptom, so will hitting the accelerator. In fact, it seems any sudden application of torque to the driveshaft will create this noise. I now suspect either the universal joint or the center support bearing! I also assume that as this problem gets worse, it will begin to make noise in drive as well as reverse. Can anyone think of a way to narrow down the problem between the u-joint and the bearing?? Either way, this noise is driveshaft related, and is coming from somewhere between the center to the rear of the car. And can anyone guess why such a problem decides to show itself in reverse first, as opposed to all the time? Are the wheels torqued more in reverse than in drive at very slow speeds? Thanks again
-travis

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'76 300D
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