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  1. #1

    New Rotor Contacts the Brake Caliper

    I swapped rotors and pads on my '96 GTS and while doing so I noticed that there is far more clearance (approx .090") on the inboard side of the caliper than the outboard (approx .020" on the passenger side, less on the driver side). I thought to myself that it was peculiar but when I went to bed in the new pads it was obvious that as the temperature of the caliper/rotor increased the clearance between the brake rotor and this little "nub" on the caliper decreased to the point where it was making contact. What is going on here?? I've measured the new rotors (distance from the hub mounting surface to the friction surface) and nothing stands out as hugely different other than the thickness of the new rotors (1.268") verse the used rotors (1.230").



    Last edited by 71firebird400; 11-15-2016 at 11:33 PM.

  2. #2
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    OK I will ask, Who's aftermarket rotors are they? Another area to possibly measure would be the inner face of the rotor where the Lug nuts are.

    Looking at the pictures it seems that the lug nuts are loose, if you fully tighten them down onto the disc face that may push the disc onto the hub a bit more and solve your problem. If you cant get the lug nuts to tighten down onto the disc use some open ended lug nuts so that the disc is pressed fully home onto the hub.

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    Yeah what he said. But what pads are they too. Flat washers also make a great way to hold the rotor tight on the hub in lieu of having the wheel on.
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    You can see that is kind of the case in the last picture. The space does not look parallel.
    96 GTS (# 33, Bone Stock), 66 Mustang Convertible, 66 Mustang Hardtop, 69 Corvette Roadster

  5. #5
    Thanks for the responses. You are correct, the lug nuts are not tight in the picture. However, the contact occurred while driving when the lug nuts were torqued to the spec in the service manual. Those pictures were taken immediately after removing the wheel from the car so the rotor was still flat against the hub, but it's a moot point since this is occurring while driving.

    It would appear the rotor needs to move inward approx .050" to truly be centered in the caliper. Unfortunately there is no easy way to accomplish that as far as I can see. I am working with the manufacturer who has been very responsive but I wanted to see if anyone here had relevant insight that would help determine what's going on here and what the purpose is of the little protrusions on the caliper (where it's making contact).

    - - - Updated - - -

    Quote Originally Posted by dave6666 View Post
    Yeah what he said. But what pads are they too. Flat washers also make a great way to hold the rotor tight on the hub in lieu of having the wheel on.
    Hawk HPS pads.
    Last edited by 71firebird400; 11-16-2016 at 09:53 AM.

  6. #6
    Followed up with the rotor manufacturer and the dimension I measured f from the hub mounting surface to the inner friction surface matches their drawings. All they could think of is that perhaps the ID of the "hat" may not be opened up enough to allow the rotor to sit completely flat on the hub. I'll be investigating later tonight. As far as I know there is no way to move the calipers inward by fumbling the caliper bolts or some other installation error but if anyone has any ideas please let me know.
    Last edited by 71firebird400; 11-16-2016 at 03:59 PM.

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    Remove the caliper, remove the rotor, check the hub is perfectly clean and check the inner face of the new disc. Also make sure there are no bits of debris on the brake caliper. refit everything and bolt up the disc on the hub and spin with out the wheel on making sure the disc is not warped

    See how that works out
    Who's Discs are they?

  8. #8
    I put the stock rotor back on the car hoping to determine the cause of the issue. I was trying to verify if the "offset" of the rotor (OEM vs aftermarket) was different or if there was perhaps an issue with the aftermarket rotor sitting flush on the hub. Upon bolting the stock rotor back onto the car it is evident that the rotor is NOT centered in the caliper but is obviously sitting towards the outside almost identically to the aftermarket rotor. The OEM rotor is worn, and thus thinner, providing slightly more clearance. I used two lug nuts (tightened) to secure the rotor in place, the caliper bolts are also tight. I verified that the rotor was sitting completely flat on the hub by placing a drop of anti-seize on the hub face; it was completely flattened when I clamped the rotor in place with the lug nuts.

    Pictures of the stock rotor on the car-




    Not much more clearance, but enough that it never made contact with the caliper as the new rotor does. I cannot explain why the rotor is sitting too far outward, there is no adjustability in placing the caliper on it's mounting bolts and obviously the hub is fixed. There is a "corrosion prevention gasket" (as the FSM calls it) between the hub and the knuckle but I do not believe there is any adjustability there either. It appears that we have one of three scenarios-

    1. All Vipers are like this, to some degree, and the disc is not centered in the front caliper.
    2. Both of my front calipers are out of spec to similar degrees (since they both sit very similarly).
    3. Both of my steering knuckles are out of spec to similar degrees (again, since both sides are doing the same thing).

    Anyone have a picture of their front brake assembly showing the relationship of the caliper to the rotor?

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    Which rotors are those? I know you were deliberating about which brand to use. Ah the joys of the aftermarket. If you can wait, I'll pull my front wheel off this weekend to verify for you. My brakes are original, so I should be able to get you some accurate info. to compare with.

  10. #10
    Quote Originally Posted by Camfab View Post
    Which rotors are those? I know you were deliberating about which brand to use. Ah the joys of the aftermarket. If you can wait, I'll pull my front wheel off this weekend to verify for you. My brakes are original, so I should be able to get you some accurate info. to compare with.
    The rotors are Stoptech but the second set of photos are the OEM rotors which exhibit the same issue; I don't think this is a rotor issue unfortunately. Stoptech has been great to work with, hence my reluctance in naming them for fear of having folks jump to conclusions before I've got this sorted out.
    Last edited by 71firebird400; 11-16-2016 at 11:29 PM.

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    Is there any play in the hub? When was the last time the wheel bearing was torqued? might want to check that?

    Stoptech have a good reputation so I doubt there would be an issue there. I have seen issues with slotted and dimpled rotors by EBC
    Last edited by Fatboy 18; 11-17-2016 at 01:37 AM.

  12. #12
    Quote Originally Posted by Fatboy 18 View Post
    Is there any play in the hub? When was the last time the wheel bearing was torqued? might want to check that?

    Stoptech have a good reputation so I doubt there would be an issue there. I have seen issues with slotted and dimpled rotors by EBC
    Haven't touched the wheel bearing but there is no detectable play on either side; the car only has 12k miles. The hub face was cleaned with a wire brush as was the back for the rotor and also the mounting surfaces for the brake caliper. Again, this is occurring on both sides on the front. I would be interested in seeing a picture of someone else's stock setup and how well the rotor is centered in the caliper.

  13. #13
    Have the calipers ever been repainted? Wondering if the mating surface where the caliper bolts to the hub have become thicker and are pulling the caliper tighter on that one side...

    Another possibility is if the wheel bearing has ever been replaced with an aftermarket it could maybe cause that small offset issue.
    Last edited by Boosted Motorsports; 11-17-2016 at 09:53 AM.
    Check out my YouTube Channel for Viper DIY Videos and other content! - Boosted2k

  14. #14
    Quote Originally Posted by omalley_808 View Post
    Have the calipers ever been repainted? Wondering if the mating surface where the caliper bolts to the hub have become thicker and are pulling the caliper tighter on that one side...

    Another possibility is if the wheel bearing has ever been replaced with an aftermarket it could maybe cause that small offset issue.
    The brakes were entirely stock (pads/rotors) and the car only has 12k miles so I am reasonably certain the calipers were never painted or coated. Also, they have the stock Viper logo on them which would've been hard to recreate. The wheel bearings (hubs) are also stock pieces as far as I can tell. They say "Made in Italy" if I'm remembering correctly and look original to the car.

  15. #15
    Here are some pictures of the hubs, maybe someone can spot if they see anything suspect-



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    OK, I know you asked for stock but here's a pic of mine.
    These are BAER 2 Piece Eraddispeed Slotted only rotors. I panted the calipers myself using brake caliper paint. As you can see its close, but it does not touch
    Note: My wheel studs are also much longer than your stock ones


  17. #17
    Thank you for the picture! It appears that my rotor/caliper are sitting close to the same place as yours. The Eradispeed rotor is 1.25" wide (.020" narrower than the Stoptech rotor I am using) and has a distance from the hub to the inner friction surface of 2.125" which is the same as the Stoptech and OEM rotor (verified this through Baer).

    Stoptech has gone to great lengths to figure this out and has concluded that the OEM rotor/caliper position is flawed and that stacking tolerances are the reason I am experiencing an issue. Their best guess is that during R&D the brakes were located with the hub bolted to the knuckle and that perhaps the "corrosion prevention gasket" was inserted between the two components at a later date. It does seem some what likely to me as the amount the rotor is pushed outward is very similar to the overall thickness of the gasket.

    I have ordered a set of new gaskets to see if they're any thinner than what was installed on my car from the factory. If that does not help the situation then I am limited to machining the rotors (to make them thinner) or machining the calipers (to mount them further outward).

  18. #18
    dang. Now you have me nervous as I just bought a set of stoptech rotors for my car. Really hope this is a one of issue as I didn't see any fitment concerns when I was researching rotors.

    Guess if this happens to me, I would probably just shave that piece down on the caliper a little bit, assuming it wont negatively impact anything.

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    That's what I would do

  20. #20


    Provided the rotor is made to 32mm (1.26") in thickness, 54.85mm (2.16") is what you should be looking at.

    RacingBrake options for G1/G2 are available here:

    http://www.racingbrake.com/category-s/7323.htm

    Prices include XT910 street performance brake pads.

  21. #21
    Quote Originally Posted by Racingbrake View Post


    Provided the rotor is made to 32mm (1.26") in thickness, 54.85mm (2.16") is what you should be looking at.

    RacingBrake options for G1/G2 are available here:

    http://www.racingbrake.com/category-s/7323.htm

    Prices include XT910 street performance brake pads.

    Thank you for the information. It appears your hat depth is .900" (54.85mm - 32mm = 22.85mm), which moves the rotor .043" in the right direction for me. It also appears your rotor (32mm) is .008" thinner than the Stoptech rotors (1.268") which gains me an extra .004" of clearance on both sides. Taking these factors into account it seems as though your rotor is actually positioned very near to the centerline of the caliper. Obviously I am a bit gun shy on ordering a pair of $700 rotors due to my experience with these Stoptechs; would you agree with my math? I'd hate to order a set and discover I dropped a number somewhere.

  22. #22
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    Quote Originally Posted by Racingbrake View Post


    Provided the rotor is made to 32mm (1.26") in thickness, 54.85mm (2.16") is what you should be looking at.

    RacingBrake options for G1/G2 are available here:

    http://www.racingbrake.com/category-s/7323.htm

    Prices include XT910 street performance brake pads.
    They look great, Do you do rears too?

  23. #23

  24. #24
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    Quote Originally Posted by 71firebird400 View Post
    Thank you for the information. It appears your hat depth is .900" (54.85mm - 32mm = 22.85mm), which moves the rotor .043" in the right direction for me. It also appears your rotor (32mm) is .008" thinner than the Stoptech rotors (1.268") which gains me an extra .004" of clearance on both sides.
    Not mentioned are the actual manufacturing variances from the design drawing.
    Jim

  25. #25
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    Quote Originally Posted by 71firebird400 View Post
    Thank you for the information. It appears your hat depth is .900" (54.85mm - 32mm = 22.85mm), which moves the rotor .043" in the right direction for me. It also appears your rotor (32mm) is .008" thinner than the Stoptech rotors (1.268") which gains me an extra .004" of clearance on both sides.
    Just as a comparison, I measured the equivalent dimensions on an EBC rotor that I still have sitting around several years after selling my 2002. Calculating/measuring the way you referenced above, hat depth is 0.857" ( 54.343mm - 32.563mm = 21.78mm). Rotor thickness is 32.563 mm= 1.282 inches
    Last edited by AZTVR; 11-18-2016 at 08:37 AM.
    Jim


 
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