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  #1  
Old 09-19-2000, 10:26 PM
Mike Murrell's Avatar
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Vehicle is a '91 300-SEL.

Had a local MB independent shop do a turn-key brake job today. Front and rear rotors were replaced.

I noticed the rear rotors have what I'll call a cross-hatch pattern, something like I've seen inside 4 stroke Japanese motorcycle cylinders. The front rotors had a circular pattern that followed the flow of the rotor.

Is there a reason for the difference between what the front and rear rotors look like?

Thanks for your time.


Mike Murrell
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  #2  
Old 09-19-2000, 10:30 PM
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Location: New Bedford, MA USA
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New rotors should have some evidence of a final surface grinding to spec. I suppose a circular pattern is possible. Can you feel any ridges in the front rotors. If so, then they are not new and have been turned or refurbished.

------------------
Jeff Lawrence
1989 300e
2000 Dodge Grand Caravan SE

[This message has been edited by jeffsr (edited 09-19-2000).]
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  #3  
Old 09-20-2000, 01:13 AM
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Location: Austin, TX
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Mike,

I'm curious, how much did that brake job set you back?

Mr. BILL
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  #4  
Old 09-20-2000, 01:21 AM
CMuc's Avatar
mucman
 
Join Date: Jul 1999
Location: Port Coquitlam BC, Can
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Some after market rotor manufacturers do a final suface treatment with a disk and some don't. I suspect they are two different brands. When I resuface rotors, after the final cut, we have a "3M" drill attatchment specifically designed for this final proceedure.

[This message has been edited by CMuc (edited 09-20-2000).]
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  #5  
Old 09-20-2000, 08:38 AM
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Location: Gainesville FL
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I concur. They are probably from different manufacturers. I prefer the non directional pattern. If the final roughness is too great the brakes will take more effort for a period on time (till they wear in).

The phono record type continuous machine turned rotors can cause a number of noises due to the pads trying to screw themselves up the rotor.

If you have no problems I wouldn't worry about it as the surface will be gone in a few thousand miles anyway.

------------------
Steve Brotherton
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician
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  #6  
Old 09-20-2000, 11:28 AM
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Location: Orange, OH, USA
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The cross hatch type pattern is the result of type grinding process. My machinist buddy called it blanchard (sp?) ground. For larger surfaces, like a rotor, it results in a flatter surface. Suffice to say, a rotor ground in this fashion should be better.
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  #7  
Old 09-20-2000, 12:00 PM
Mike Murrell's Avatar
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Thanks to everyone for their input. I was &
still am just "slightly" suspicious that the
front rotors were "turned". By bill indicates
I paid $81.00 a piece for 2 news ones. Guess
I'll never know. The Pros that responded made
it clear that there are different cuts available. Onward.

Mike Murrell
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  #8  
Old 09-20-2000, 12:43 PM
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I seriously doubt that someone would turn the rotors and charge for new. The main reason I doubt it is that it is too easy to prove. All you have to do is measure the thickness. The new rotor is 28mm thick and has a wear tolerance of 25.4mm meaning 2.6mm of wear or machining. If the rotors had worn through one set of pads or more they probably were half way through that tolerance. That tolerance is just .052" per side.

------------------
Steve Brotherton
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician
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  #9  
Old 09-21-2000, 01:39 AM
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Join Date: Jul 1999
Location: San Francisco, Ca
Posts: 2,267
Mr. Bill, just as a comparative,
I had the front pads and rotors
changed on my C280 (ind. shop)
total $420 ,rotors 85 ea. pad set $91.
?

------------------
1979 300D
133K miles
1989 300SE
1995 C280
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