Rear caliper contact with rotor

Discussion in 'Boss 302 and S197 Technical Forum' started by awdowns, Sep 11, 2018.

  1. awdowns

    awdowns TMO Beginner

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    Hey guys,

    First post here. I have a '11 GT with the Brembo brake package. I did a track day over the weekend and noticed a very slight rubbing on the outside edge of the the rear rotors on both sides. Right in the rust ring on the very outside where the pad doesn't touch. The axle seals also leaked a very small amount of fluid, drivers more than passenger side.

    I checked all of my wheel bearings before heading to the track and they all felt solid. I checked them after the track and I can't feel any movement in them. I pulled he drivers rear caliper off the next day to check it out and noticed the caliper made light contact with the rotor. I measured the axle end play with a dial indicator and got .015". Looks like Ford allows for .030" max.

    Has anyone seen this happen before? I searched around the forums here and didn't come up with anything.

    I will be replacing the seals and the bearings as well since I will be doing 90% of the work anyway to get the seals out. But is there anything else I should do while I am in there? I want to make sure I am not overlooking something else that could be contributing to the issue.

    The suspension on the car is stock aside from lowering springs. The car has ~48,700 miles on it. Pads used were the Hawk HPS 5.0, but I will be definitely switching to a track only compound next time I head out. The rear brakes look like they transferred a lot of pad material build up onto the rotors. Tires used were MPSS, still on stock Brembo package wheels 255/40-19

    20180909_111540 (Large).jpg 20180909_111735 (Large).jpg
     
  2. VoodooBoss

    VoodooBoss Rick Moderator

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    Welcome to TMO. How did the pads look? I'm sure you're going to anyway but clean off the wheel sensor when you put it back together.
     
  3. awdowns

    awdowns TMO Beginner

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    Thank you!

    I didn't pull them out of the caliper, but I took a quick look at them and didn't notice any abnormal wear. They both looked like they wore evenly.

    I did clean off the wheel sensor, dust shield and brake cleaned the whole area off before putting it back together.
     
  4. Grant 302

    Grant 302 OPM Spent: $587,402 Moderator

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    Yes, but it's not common. I believe it's from the bracket bending and the mis-alignment allows contact. I'd replace the whole assembly. Not sure if the bracket is available separately.
     
  5. Coz

    Coz TMO Race

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    The 2011 had a regular clutch-pack LSD in lieu of a Torsen, correct? If so, you could have worn clutch packs that result in more axle play.
     
  6. smallblock

    smallblock TMO Advanced

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    Believe it or not, this is completely normal for stick axle mustangs. Axle flex allows the outside wheel rotor to angle inward on the bottom and outward on the top (positive camber) to the extent that the rotor will make contact with the caliper bracket. You must machine the area of contact on the bracket to make room, or go with a Performance Friction/Roush rear brake kit. GT500 13.8" brakes make this issue worse and fixed calipers are out of the question.

    As far as axle seals go, they are a consumable on these cars due to all the flex mentioned above combined with heat from the brakes. I suggest replacing once a year if you HPDE often. Losing one at the track is no fun. Use only Ford parts, as they are a much higher quality than the aftermarket seals I have encountered.
     
    Last edited: Sep 11, 2018
  7. smallblock

    smallblock TMO Advanced

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    Look at the positive camber in the photo below with DOT tires. This illustrates the tire, wheel and axle flex present and typical on our cars. Now add to it Stickier race tires: more grip = higher G's = more flex. I measured this example at over 2 degrees positive camber, easily equating to over 1/4" movement at the top of the rotor where it contacts the bracket.

    The other solution is a Cortex floating 8.8 axle which is a work of art but starts around $7000.00

    [​IMG]Untitled by smallblock, on Flickr
    [​IMG]Untitled by smallblock, on Flickr
     
  8. Coz

    Coz TMO Race

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    Any thoughts on whether Moser or Strange Street Axles would flex less?
     
  9. smallblock

    smallblock TMO Advanced

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    I replaced my axles as a precaution with OEMs. Dean at Kohr always used OEMs in his race cars. Now if I did it again I might give Moser a shot. They claim they are stronger but that doesn't mean that they have a higher resistance to bending, it could actually be the opposite. I would ask Moser what the difference is in materials they use vs. OEM, and what tests they have performed. I would want to examine and research the metallurgy for myself before giving in to their marketing hype. It's easy to make claims when they know no weekend warrior has the equipment to test their claims.
     
  10. awdowns

    awdowns TMO Beginner

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    Thank you for the replies, guys!

    That image really puts the stress of the axle in perspective and helps make sense of what happened. I was curious if something like that could be happening but was thinking it would ruin the wheel bearings and make itself more apparent. I guess I will be clearancing the brackets when I pull it all apart to replace the seals.

    I was definitely planning on using the Ford parts for the repairs.

    Grant,

    I had a thought about brackets or guide pins somehow deforming as well, but it was happening to both sides, which made me think a double failure like that would be odd. Looking at at them with the car up in the air everything looked centered and nothing was out of the ordinary.

    Coz,

    My car would have the clutch type rear in it, I don't think the Torsen was available on the GT until the '13 track pack. I did measure end play which was still within spec.
     
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  11. jpt3

    jpt3 TMO Advanced

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  12. smallblock

    smallblock TMO Advanced

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  13. jpt3

    jpt3 TMO Advanced

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    Interesting do you know what’s different about the caliper bracket with this vs stock?


    Sent from my iPhone using Tapatalk
     
  14. smallblock

    smallblock TMO Advanced

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    It's milled from billet aluminum vs. cast iron, the bridge is wider so the rotor does not contact, and positions the caliper for their 13" 2pc rotor using non-GT500 axle brackets.
     
  15. jpt3

    jpt3 TMO Advanced

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    Interesting so my new car actually has these and I wasn’t sure what they were. Do you know if the gt500 rotors still fit on them?
     
  16. Coz

    Coz TMO Race

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    GT500 rear rotors are 13.8" so if these caliper brackets only move the calipers outward to 13" it won't work with them.
     
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