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+--- Thread: OH NO! Did I just cook my rear disk!? (/showthread.php?tid=5586)
OH NO! Did I just cook my rear disk!? - TINK_imp - 05-15-2016
So I come home after a short ride this morning, put the bike up on the center stand, spin the wheel to lub the chain... spin the wheel... Houston, We've Got a Problem.
It seems that the rear brake is dragging, excessively. So much so that the rear disk is showing signs of blueing, overheating.
The brake pads are brittle in places and small chunks of pad have broken off.
WHAT THE HECK IS GOING ON HERE!?
Could I have unknowingly had my foot on the rear brake pedal, thus overheating the rear brake? If so, then why today? What did I do differently during today's ride?
Pulled the caliper and checked the slide pins, they seem to be fine.
Bled the rear brake, but I don't think this is a hydraulic issue as the piston does appear the retract when I let my foot off the pedal.
Signed, Baffled.
RE: OH NO! Did I just cook my rear disk!? - Cormanus - 05-15-2016
That doesn't sound good at all, Tink? What now? New pads and test ride?
RE: OH NO! Did I just cook my rear disk!? - Lord Popgun - 05-15-2016
Sounds like you were dragging the brake. I don't know why, but you are not the first to do so. He warped the rotor and it had to be replaced.
Cormanus, Checking the rotor runout would be first on my list.
RE: OH NO! Did I just cook my rear disk!? - TINK_imp - 05-15-2016
(05-15-2016, 07:21 AM)Cormanus_imp Wrote: That doesn't sound good at all, Tink? What now? New pads and test ride?
Yep, replace the pads and see what happens. Worst case I but a rotor too $$$ :-(
RE: OH NO! Did I just cook my rear disk!? - Lord Popgun - 05-15-2016
Tink, FYI if you don't have a manual, rear runout spec is 0.30mm or 0.012in
RE: OH NO! Did I just cook my rear disk!? - Pterodactyl_imp - 05-15-2016
As Popgun says, check rotor runout and thickness. The latter should not be a problem but have a look any way. That just ensures the rotor is still good. Blueing in itself is not a problem and the rotors will not be "cooked". A light skim or sand may be necessary if glazing or deep grooving exists.
Next step is to troubleshoot the problem. I quote directly from the '13 service manual:
Brake drags
~ Contaminated brake disc/pad
~ Misaligned wheel
~ Badly worn brake pad/disk
~ Warped/deformed brake disk
~ Caliper not sliding properly
~ Sticking caliper piston
~ Clogged/restricted fluid passage.
I don't know if your mechanical skill is equal to your undoubted photographic skill, but, if so, none of the above procedures or checks will be challenging. You have already indicated in your post that you are capable of all the above. A manual is useful however torque settings, caliper limits and other tips can be sought from forum members.
From your initial inspection you indicated that the hydraulics looked OK and the piston retracted. I would suggest that in checking the piston you pull the caliper apart and check for scoring (or "ringing") and that it is in round with the cylinder ID and piston OD within limits. Very light scoring can be removed by rubbing with fine (1200) wet and dry. Replace all the seals and lubricate both the piston seal and piston with Dot4 before assembly. There is some silicone grease points that need attending to so the assembly doesn't bind.
If the caliper is in good knick then it is back to the hydraulics. First check the pedal and linkage is completely free from any binding. Next step is master cylinder strip and inspection.
And so it goes. Plenty of advice from the forum to help. It is highly unlikely you have been riding the brake pedal, but if your not sure then, when all is back together, be careful.
Cheers and good luck.
RE: OH NO! Did I just cook my rear disk!? - TINK_imp - 05-16-2016
Today's update
The heat had warped the steel backing plates on the brake pads thus holding pressure on the rotor after the piston retracted.
This of course kept heating up the rotor as I rode.
Still have no clue as to what the root cause of the initial over heating episode was, but once the steel plates were warped the damage continued.
Rotor run out was right at the .008" spec.
Managed to tweak it back to .004"
Time will tell (after several heat cycles) if the tweak will hold.
Waiting on new pads to arrive.
Stay tuned...
RE: OH NO! Did I just cook my rear disk!? - LongRanger_imp - 05-16-2016
Yikes.
OH NO! Did I just cook my rear disk!? - Elipten_imp - 05-16-2016
Wow never seen that before
Check the pads release before next ride
Sent from my iPhone using Tapatalk
RE: OH NO! Did I just cook my rear disk!? - kmoney_imp - 05-16-2016
That's a crazy amount of heat. I've never seen a backing plate rainbow before.