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Old 07-20-2014, 06:40 PM   #1
Ramanonos OP
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R100GS disc rotor or wheel hub problem

Just bought a mint '96 R100GS (17k miles) and noticed immediately a pulsation and squeal in front brake that got progressively worse. Brembo calipers stock. I did the obvious thing with washing up the caliper, pads (plenty pad left) and rotors. Sanded pads with light-grit paper and applied small amount of grease to back of pads. Still... Problem persists. So I figured rotor was warped. So I took a metal fork and put up against fork to test.

Sure enough disc rotor rubbed at a high point. Rotor is solid metal so as far I can tell, it's likely original stock. But the story isn't over. I did the same test to check if the wheel is bent. So I took the same lobster fork and sure enough, rubbed on the wheel hub at same high point as the rotor.

Now I don't know whether it's a problem with my disc rotor or the wheel hub... How would I determine? Further, I'm not sure how to determine next steps (repair rotor with a hammer or buy new -- or repair hub with spokes or buy new). Thanks in advance.

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Old 07-20-2014, 07:32 PM   #2
H96669
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I had a similar assembly...wheel/rotor. When mounted on the jig and yes I have a wheel jig to check for deflection, the rotor was right at the top of the max allowed lateral deflection.

I removed the rotor from the hub, cleaned the surfaces with the small file as they were showing high spots and then remounted the rotor.

Back on the jig and well within the specs in the manual.
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Old 07-20-2014, 07:45 PM   #3
jackd
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That isn't a '96 GS - I would say it is an '88 or '89. The front disc on those is a non-floating solid type, unlike the later ones which had ventilating holes and floated. I run the earlier type of rotor on my '94. With the solid mounting, there might be a tendency for warpage to show up during brake applications. The later floating rotors probably hid any issues of this nature. I would probably suspect you have the original brake pads. Throw in some new ones and the squealing will probably go away.
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Old 07-20-2014, 07:52 PM   #4
Ramanonos OP
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But how would you explain the whole wheel itself being off? That would suggest not the rotor, but the higher radial wheel being off against the fork - from which caliper is mounted. Gives me 2nd thoughts. I was seconds away from buying a 400 rotor...


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Old 07-20-2014, 08:06 PM   #5
Ramanonos OP
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Yes, I meant an 89. I have learned that the first r100s had a solid disc. I think you're right about original pads. They looked glazed with soot. Just figured they were good with a spray/scrub/sand/grease. This bike sat still for a decade. Still.. How does that explain my fork test in original post (fork stopped wheel at high point, but wheel hub as wheel)


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Old 07-20-2014, 10:49 PM   #6
squish
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I would take the wheel off and mount it to a trueing stand
I'd measure the latteral and radial runout of the rim, the hub and the rotor.

Then I'd flat plate the rotor and check to make sure it was flat, both at the swept areas and the mounting points.

I would also the check the rotor mount points on the hub.

But on a trueing stand you will see pretty quick if things are much out of wack.
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