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Thread: Incorrect offset on JHM 2-piece front brake rotors for C5 RS6

  1. #1
    Registered User
    Join Date
    Apr 2017
    Waterford, MI

    Incorrect offset on JHM 2-piece front brake rotors for C5 RS6

    I bought my RS6 with JHM 2-piece lightweight rotors already installed. I have been hearing a scraping noise from the front brakes when cornering hard and finally found the source. The rotor is not centered in the brake caliper and is much closer to the inside of the caliper than the outside. This allows the inner brake pad guide pins at the bottom of the pad to contact the rotor when it flexes due to heavy cornering forces. There is a witness mark on the inside edge of the rotor that matches the size and location of the pad pins on the caliper.

    I can't find any discussion about this issue. Is this a known problem?

    I filed about .050" off the inside pins on the caliper to give additional clearance and that appears to have fixed the issue when cornering moderately hard, but I suspect they will still contact the rotor if I really throw it into a corner, which kinda defeats the purpose of having a sharp handling car with sticky performance tires.

    The proper fix appears to be to shave 1-2mm off the caliper mounting bracket where it bolts to the upright to move the caliper inward and center it on the rotor. A quick and dirty fix would be to put a 2mm spacer behind the rotor to space it outward, but that will reduce the contact area between the center bore of the rotor and the hub. This is a small enough contact surface already and I don't want to reduce it any further.

    I should have snapped some pics when I was working on it last night as they would show the issue clearly vs. trying to explain it.

  2. #2
    Registered User hahnmgh63's Avatar
    Join Date
    Feb 2007
    Roy, WA
    The correct fix would be to scrap the JHM rotors. You can try contacting them and see if they'll make them right (new hats? updated design?), or go back to OEM rotors rather than modifying the caliper from the way it was designed.
    2003 White RS6 2013 Midnight Blue S5
    2013 Daytona RS5 2x944 Turbo's 1974 911 w/'91 3.6ltr motor
    Roy, WA

  3. #3
    Registered User
    Join Date
    Mar 2007
    Evil Empire
    Milling caliper mounting bracket doesn't sound like a good idea, since it'll compromise it's strength.
    Spacing the rotor out doesn't sound good to me either, but is better out of two options.
    Third one would be getting a new (beefier, to account for more leverage) caliper mounting bracket made.

  4. #4
    Registered User lswing's Avatar
    Join Date
    May 2011
    Eugene, OR, again...
    Use " jhm rotors" in Google. You'll find a multitude of issues and poor fitment or warping. I'd just scrap them and put new stock OEM rotors from Zimmerman on.
    Ace/Edge TC - Tozo Trans - MTM TCU - REVO/ME7 tune - Wagner IC's w/ Venair Hoses - Aux Radiator delete - Hotchkis Sways - Hawk HPS Pads - Koni Sport Struts - Scroll KO4 Turbos - Devil's Own WM - 421whp/452wtq on Mustang Dyno -

  5. #5
    Registered User G2's Avatar
    Join Date
    Apr 2012
    Eugene, OR
    While the old design fit fine, the hat design prevented being able to machine the rotors. Warped rotors were another negative. OE rotors fit perfect and hold up better from what I have seen.

    FWIW I have new OE Zimmerman rotors for sale that are posted up. One set left now.
    Cheers, G2/Gary
    C5-RS6/KWV3/Revo/H20 Inj./Custom BBK/Custom cooling/CNC arms \ VW Touareg V10 \ B7A4 2.0T Avant \ Mk1 Callaway Scirocco \ /

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