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  #1  
Old 12-20-2003, 10:30 AM
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brake sensor question

The Yellow light on the dash has started to come on indicating that I need new break pad for my 300d turbo. Bad timing with the holidays upon us. Do i have a few weeks to get this done or is this a matter that should be dealt with right away? Also, should I go to a mercedes mechanic or is that the sort of thing that anyone can handle?

Thanks in advance for any advice.

Best regards to all.

Joe A
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  #2  
Old 12-20-2003, 11:41 AM
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You probably have a few weeks. Brake easily and lighlty if you must wait. How many miles on your rotors? As far as the pads, you can easily do the work yourself if you know what to do. Otherwise, you'll have hell with things like trying to remove the old pads without compressing the pistons a little. Better get a buddy who has done it before. There are probably some detailed istructions here if you search them out.
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  #3  
Old 12-20-2003, 12:15 PM
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thanks for the info. Not sure how many miles are on the rotors. I bought the car 11 months ago and have put 3,500 miles on it. I'm at 154K.

Since I've had the car, there has always been a VERY loud squeeking sound when you apply the breaks while in reverse.. Do you think that's a related problem or something else entirely?

Joe
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  #4  
Old 12-20-2003, 12:21 PM
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Click on the D.I.Y. tab at the top of the page and scroll down to the last article. This gives you a step by step description of changing pads and sensors (although it doesn't go into determining if you need to replace rotors or not).
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  #5  
Old 12-20-2003, 12:57 PM
gstigler
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Since you just got the car and the pads are shot (unless the sensor is bad), I would recommend replacing rotors, pads and the brake hardware. Even if the rotors still have life left in them you're better off spending another $150 and getting all new parts. Obviously stopping is important and if your going to drive the car more than another 10k miles it will be worth it.

The DIY articles on this site are great. If you have some mechanical inclination you should be able to do the job in minutes per wheel. Once you have everything apart to replace the pads, the rotors only require two more bolts to be removed. Make sure that you used anti-squeel compound between your pads and the calipers. With the age of your car it's worth the small to replace all the hardware as well (springs, pins, bolts).

Also, use brake parts cleaner on the calipers, all female threaded holes, wheel hub and contact surface between the hub/rotor/wheel. The cleaner can also be used to help loosen the pads if they are stuck to the caliper piston.

Give it a shot, you'll save some cash.
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  #6  
Old 12-20-2003, 12:58 PM
gstigler
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Oh yeah, and replace the sensors. If your car is like mine it has them on three wheels.
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  #7  
Old 12-20-2003, 02:28 PM
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I don't see why you should replace the rotors if they are not worn out. My light came on this week and I changed the front pads on my 85 300td in about 40 minutes. Pads and two sensors cost $35.
Pull the wheel. drive out the pins that hold the pads in place with a hammer and nail, removing the tensioning spring, disconnect sensor wires, pry caliper pistons back by using a screwdriver between rotor and old pads, put lubricant on back of new pads, install.
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  #8  
Old 12-20-2003, 04:02 PM
gstigler
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Everyone has their own opinion on rotor replacement and both sides can be argued. My thoughts are that when you're dealing with an unknown and the parts are relatively cheap, it's best to replace the part. This goes two fold when dealing with brakes.

Your rotors should have a minimum thickness stamped on them. At a minimum measure the thickness to see where you stand. The fact is that those rotors have been used through at least one set of pads, maybe more. I'd hate to see you replace the pads and then have to pull it all appart again in 5-10k miles and replace pads and rotors because your rotors warped.

I see this much like changing your oil....preventative maintainence.
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  #9  
Old 12-21-2003, 07:52 PM
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Unless the rotors have a significant lip on them which indicates severe wear, I'd just slap in new pads. As a matter of fact being a professionl mechanic I receive many industry magazines not sent to the general public, and the consensus of auto mfgs in articles written in these magazines is, don't replace rotors unless necessary. Also there are neat little teflon coated plates that go on the back of the pads and really reduce brake noise.

Peter
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  #10  
Old 12-21-2003, 09:42 PM
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joe

i had the same question on my 87 about 3 weeks ago or more. since the question i got 900 miles on them without any babying along. so i'd say the means get the job done but don't panic. i haven't looked but it wouldn't suprise me if there is 25% of the pad left when i take them down this week.
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  #11  
Old 12-22-2003, 12:27 PM
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I've done mine at various times when the light came on, and based on my experience, I would gauge that there is about 7500 wear miles of material left over before your pads wear to the point of scoring the rotors.

I believe MB likes to err on the safe side.

Don't know what model you own, but vehicle weight and driver input are varying factors...but I believe you can probably go a month or two safely before you really need to give the brakes a look...
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  #12  
Old 12-22-2003, 12:55 PM
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I would pull a wheel and take a look.

After your brake light first comes on, you have plenty of time to line up parts, tools, etc. If I understand correctly, the light will eventually go out and this does not mean your brakes are suddenly healed but that the sensor is now totally gone.

I was a complete novice when I did my front rotors and brakes. A very simple but dirty job that you can do for about $150. Anywhere else, it will be $500+.

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  #13  
Old 12-22-2003, 01:05 PM
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G-Benz

that kinda fits what i was thinking regarding the sensors vs the pads.

i got my 87 420sel front setup for 126 delivered included both new rotors, pads, sensors and paste and a couple misc pcs of fasteners.
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Craig

1972 350sl Red/Blk 117k
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See My Cars at:http://mysite.verizon.net/res0aytj/index.html

Pound it to fit then Paint it to match!

There is only First Place and Varying degrees of last!

Old age and deceit will overcome Youth and Enthusiasm every time!

Putting the square peg in the round hole is not hard... IF you do it fast enough!

Old enough to know better but stupid enough to do it anyway!
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  #14  
Old 01-01-2004, 12:17 AM
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To put things in perspective, on my 95 E320 the pad thickness is 11 mm when new and 2.5 mm when the wear sensor makes contact (23% of pad thickness remaining). Don't wait too long though. You certainly don't want metal-to-metal wear on the rotors. Two mm pad thickness is the specified discard thickness.
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  #15  
Old 01-01-2004, 12:29 AM
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If the pads are worn beyond specifications in conjunction with worn rotors then there is the possibility of the piston not being long enough to accomodate the wear and thus the piston can cock sideways in its bore and possibly leak or cause damage.

Minumum thickness of the pads is 2mm of friction material left. A nickel is 1.95 mm thick, so this makes an easy way to tell how much is left. If the pads are thicker than a nickel, then you have time, if they are thinner than a nickel, then they should be replaced soon.

The lights on these cars are rigged to give ample warning to when the pads need to be replaced. On my car, the light comes on with 3 mm of pad left.
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