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Thread: 77 r100rs front brake shudder

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    77 r100rs front brake shudder

    I think l know the answer, but I'm getting a pretty good shutter with hard front brake application. Pads were replaced about 1500 miles ago. The rs has the dual front disc with the holes. I'm thinking the most likely culprit is one of the discs is a little warped. I know they can't be "turned" but is grinding or machining of some sort possible? Other than a warped disc, any thoughts about a less costly culprit? Bike was put back on the road last year after a 25year nap. 19,000 miles on it.

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    I meant "shudder"

    Quote Originally Posted by Gpr100rs View Post
    I think l know the answer, but I'm getting a pretty good shutter with hard front brake application. Pads were replaced about 1500 miles ago. The rs has the dual front disc with the holes. I'm thinking the most likely culprit is one of the discs is a little warped. I know they can't be "turned" but is grinding or machining of some sort possible? Other than a warped disc, any thoughts about a less costly culprit? Bike was put back on the road last year after a 25year nap. 19,000 miles on it.

  3. #3
    Registered User jgr451's Avatar
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    I think you might be able to turn the rotors if they are warped but not worn too thin.My experience is with my 95 R100RT .The rotors started out in life quite thin and when worn,cannot be resurrected,must be replaced(expensive).I would show them to a brake specialist or measure them,before deciding whether a replacement is necessary or whether a turning could take the shudders out.
    Sometimes,nothing is a real cool hand.

  4. #4
    Monza Blue 1974 R90/6
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    This can be a symptom of loose steering head bearings. Are you sure they are tight? This is a simple and no cost option to check before you start into brake system parts.

    Barron
    Last edited by barron_williams; 08-09-2013 at 01:31 PM.

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    Thumbs up

    That's the first thing I checked.

    Quote Originally Posted by barron_williams View Post
    This can be a symptom of loose steering head bearings. Are you sure they are tight? This is a simple and no cost option to check before you start into brake system parts.

    Barron

  6. #6
    James.A
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    A mis-guided idea, but....

    If you had access to a lathe, you might be able to identify and quantify the degree of run out by chucking up the rotor and spinning it. You would need to set up a dial indicator and free spin the lathe without the benefit of motor power. You might then attempt to machine out the deviation without turning a complete new surface. You would have to do both faces. I suspect that when you were done, you would find that you have lost an un-acceptable percentage of the original thickness of the rotor. Generally, a minimum thickness spec comes into play when the brake pads wear down and allow for the possibility of the piston pushing out past the caliper seal. Also, a thin rotor is much more vulnerable to heat related issues, like warping. This would be a high risk endeavor. Only you can decide if the risk is worth saving a few hundred dollars.

    Personally, I would try it just to see if it could be done, but only on one of my bikes where I assume the risk.

  7. #7
    Registered User toooldtocare's Avatar
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    I had the same thing on my R90S with drilled rotors. They were true and new pads did not help. Cleaning them and lightly sanding them would fix the problem for a few days, then it would return. I finally took them off and soaked them in Simple Green and ran a small brush through the holes to clean them out. Apparently gunk had gotten into the holes and when hot, would migrate out and get on the disc. Problem went away after that.

    Wayne

  8. #8
    jimmy armour
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    shudder

    Hi,what I have done at times on my 1977r100s/rs, is mark both rotors 12 o clock 6 oclock ,and the other 3 oclock and 9 oclock swap them over and the o clock markings,I still have both rotors after 350,000 km,just replaced the front tire and did the swap over,guess what? I now have some shudder !!,should have left them alone ,will do the swap again if it persists,or perhaps its time for new rotors, hope this helps Jimmy, Hi me again, reswapped the rotors anjusted the pads and tested everything good as it was before the new tire was fitted again hope this assists,remember no cost to give it a try
    Last edited by JIMWJARMOUR; 08-12-2013 at 07:12 PM. Reason: add bike model

  9. #9
    #4869 DennisDarrow's Avatar
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    Sorry Bud, but for me it is replacement time. Those rotors are thin to begin with, as this is what causes them to become distorted so easily, and turning them down is out of the question. Do as you need to do; but the diagnosis problem is: which rotor is the faulty one?????.....God bless......Dennis

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    Administrator 20774's Avatar
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    I'm not sure they can easily be turned using the standard cutting blade on a lathe, etc., as I think the cutter would catch in the holes. I've heard that if a shop can magnetically pull them down on a flat table, they can then use a whole surface grinder, followed by a polishing. IIRC, the disks are just about at min thickness as is. Taking any off probably puts them outside bounds...maybe a shop wouldn't even do it considering the liability, etc.
    Kurt -- Forum Administrator ---> Resources and Links Thread <---
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  11. #11
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    $$$$ yikes

    Yikes $370 per disc!!

  12. #12
    Registered User kentuvman's Avatar
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    If it comes down to buying new rotors, I recommend Spieger Performance - they really make good rotors

    Shipped the rusted & dilipadated rotors off my R65LS through their "rotor conversion" service - the front brakes are a dream - so smooth & responsive - no shudder. You'll get floating rotors - the way to go!

    Contrarily, purchased EBC floating rotors for the K75s, trying to solve shuttering issue) EBC's not as good as Spiegler - again my experience.

    http://www.spieglerusa.com/brakes/bm...nversions.html
    Ken Tuvman
    Excelsior, MN
    K75s, R65LS, R60/5

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    Quote Originally Posted by 20774 View Post
    I'm not sure they can easily be turned using the standard cutting blade on a lathe, etc., as I think the cutter would catch in the holes. I've heard that if a shop can magnetically pull them down on a flat table, they can then use a whole surface grinder, followed by a polishing. IIRC, the disks are just about at min thickness as is. Taking any off probably puts them outside bounds...maybe a shop wouldn't even do it considering the liability, etc.
    The surface grinder method you describe is not a good solution because the problem is runout, or warpage. When the magnet pulls the disk flat, it will then grind it flat while it is there. Once the magnet is released, the rotor goes back to warped.

    Usually the rotors get warped because of internal stresses caused by various heat (clamping on the brakes) and cooling (splashing water), but after all this time, I would think that all of the stresses would be gone.

    I wonder of the rotors were removed from bike, and the reinstalled in different positions? If so, I would simply try putting them in various positions (keeping records, etc) and you may find positions that "force" the rotor flat.

    When I remove items like this, I try to mark their positions with magic marker so I can install them back in the exact same spots they came from.

    Another possibility is simply dirt got under one of the mounting locations when they were removed.

    What I would also do first, however, is figure out a way to mount a dial indicator on the fork, and measure the runout of each rotor. It is possible to straighten (flatten) them out in a machine shop if carefully using a DAKE press and lots of patience. It is worth a try if one has already determined to replace anyway. try this first, and then if it fails you can replace.

  14. #14
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    Do not attempt to or have someone else TURN rotors on a lathe. This is not the proper method. Even if you could do it, a turning operation will leave a surface that will eat your brake pads in no time. Rotors have to be ground. Blanchard grinding is the usual procedure.

  15. #15
    Monza Blue 1974 R90/6
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    Ken, from your Spiegler link, hard to tell from their web site, but is the cost $239 per rotor for them to mod the rotors you send them?

    Barron

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