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Old 07-14-2003, 12:32 PM
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Join Date: Jul 2003
Location: Sacramento, Ca
Posts: 15
Cool Brake rotors

Have been having vibration problems with the brakes on my 1991 300SE. Have replaced the rotors once but the vibration in back after about 30K miles. Anyone have experience with the Zimemrman cross drilled rotors advertised here. Do they last without getting the shakes?
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Old 07-14-2003, 01:33 PM
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Join Date: May 2002
Location: Mass
Posts: 1,127
Many folks report good results, but I have had poor results with cross-drilled rotors on 2 very different vehicles.

I never had any problems with warping, however.

The problem was premature wear on the (center) swept area at the diameter where the holes are, and slower wear on the inner and outer diameter where there are no holes. Eventually, the surface was so uneven that the pads were only contacting a small fraction of the swept area.

My current theory is that the concept is fundamentally flawed, at least for street use.

Perhaps my ugly pictures are still in the archives.
Never again for me...

Best of luck.
1986 300E 5-Speed 240k mi.
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Old 07-14-2003, 03:44 PM
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Join Date: Mar 2003
Location: Southern California
Posts: 2,055
Cross drilling conventional rotors reduces thermal capacity and creates stress concentrations that can lead to hub to OD cracks in hard use. If rotors are OEM cross drilled, that's okay, but I highly recommend AGAINST cross drilling conventional OEM vented or solid rotors.

Many rotor warp problems can be traced to improper torquing of wheel bolts. Wheels bolts must ALWAYS be torqued to specification with a torque wrench, preferably in two increments using the "star pattern", which means tightening every other bolt in sequence on a four or five lug pattern.

If you frequent a shop that just bangs the wheels on with an impact wrench, get them straightened out or find a shop that uses proper procedures.

I've never had a rotor warp problem on any of my cars, including the 2.6, and all including the 2.6 have been raced, but I ALWAYS remove and install my own wheels and always tighten them in two increments to the proper spec using the star tightening pattern. I also use anti-seize compound on the threads and wheel/bolt seating surfaces.

My rotors are worn more in the middle the the ID and OD and have numerous short thermal cracks from racing, but they have no runout and are still perfectly serviceable until they reach minimum thickness.

The only thing I have to be concerned with is new brake pad breakin, as breaking in new pads with worn rotors requires a longer and more thoughful breakin in order to achieve full effectiveness, which means light to moderate braking for about 300 miles or normal urban/surburban driving. New pads on new or refinished rotors are effectively seated in 25 to 50 miles of normal driving.

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Old 07-14-2003, 08:18 PM
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Join Date: Apr 2002
Posts: 321
how long do you expect rotors to last? in miles or as a factor of brake pad replacement[i.e., rotors every 3-4 pad replacements]?

front pair?

rear pair?

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Old 07-14-2003, 08:34 PM
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Join Date: Jun 2003
Location: Martha's Vineyard
Posts: 116
Zimmerman make high quality rotors which are cross drilled at the factory with wholes that are slightly countersunk with no sharp edges. They are OEM on many german cars and should be fine for your application.
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Old 07-14-2003, 09:27 PM
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Join Date: Feb 2003
Location: Ontario, Canada
Posts: 3,160
I love my Zimmermans.
Btw. They are CAST with the holes, not drilled.
I also agree with Duke 2.6, especially the importance of torquing.
2007 C 230 Sport.
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