Warm Back Rotor?

Discussion in 'Wheels' started by joseph.a.hart, Mar 19, 2010.

  1. joseph.a.hart

    joseph.a.hart Member

    OK, I dont know if this is a total rookie question but I just got back from a ride on my 05' DWG and I checked my tire pressure. When I took my valve cap off my rear tire I noticed my rotor was warm, almost HOT. My rear wheel also seemed to have a lot of "break dust". The pads look to be at around 50% Any input, is this normal? my front wasnt as warm as the rear either.

    NEWHD74FAN Experienced Member Retired Moderators

    Joe, it sounds like you have a lot of brake pad drag caused by the caliper in need of service. The brakes should only have a very light drag, which sounds like a light "swish" sound when the bike is moving. If it gives a loud "moan" or vibration noise when you roll the bike forward or back, you need to get the caliper serviced. New brake pads come with Service Instructions, shims & spring clip. But having an HD Service Manual is highly recommended. Also get a bottle of the proper brake fluid (read the type needed on the M/C reservoir). Good wrenching and keep us informed as to your progress.


    I forgot to add, that the brakes are single action, floating caliper type...meaning there is no outward retraction once you let off the brake pressure, the disc runnout (slight wobble) is the only thing that pushes the pads back, retracting piston into the bore, hence the swishing sound.

    The caliper floating means that the pivot pin which is lightly greased allows the caliper to be centered over the disc, again "wobbling" ever so slightly so both pads wear evenly, even though there is a piston on only one side pulling the works together.

    Thus the drag should be very light, if heavy the common failure mode is slurry of water, dirt and debris get up into the piston area contaminating the bore, as well as the pivot pin area, binding up the works or preventing the caliper from centering, wearing out one pad severely more than the other. And of course the brake fluid gets contaminated with seal/o-ring wear along with the moisture diluting it (water and broken down ethylene-glycol can oxidize and cause corrossion) so flushing and bleeding brake fluid is also recommended....no spongy brake feel allowed.
    Last edited: Mar 20, 2010
  3. biscuit

    biscuit Junior Member

    Couple of questions:do you ride with your foot perhaps resting on the brake pedal and thus lightly dragging the rear brake?Have a conscious look next time you're on the bike.

    Secondly,are the pistons failing to retract?Is there grit and brake dust around the edge of the brake piston near the extendable rubber boot.This will bind and grind and not allow the piston to retract back into the bore when the brakes are released?

    If you're able to lift the bike with a stand and elevate the rear wheel,give it a spin.It should rotate with a small effort:ie a one handed spin.It's normal for a disc brake to to maintain some pressure onto a disc.IF it takes more to spin,or only turns a partial rotation and you need a two handed spin,i would say you've got brake drag big time.

    Try looking in the self help section to see how you can fix dragging brakes.It's quite easy.Or look at Lyndall Brakes site for a good article that covers this issue.
  4. Chopper

    Chopper Senior Member

    If it was dragging abnormally you would have no skin left were you touched & the rotor would be blue, the rotors will be pretty warm to hot after a ride and pad dust is also normal. You can jack the rear up and spin the wheel if you're concerned, if it spins freely it's ok.
  5. rancid

    rancid Active Member

    im with chopper sounds pretty normal, rotors will get (EDIT) hot just from 1 or 2 uses of the brakes and will get warm just riding around

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    Last edited by a moderator: Mar 20, 2010
  6. Blue Wide Glide

    Blue Wide Glide Active Member

    I would be concerned if the rear rotor was NOT warm after a ride. This is perfectly normal. Wash the brake dust out of the caliper using some wheel cleaner and water, and don't worry about some heat, just make sure you keep an eye on the thickness of the pads. They are not very thick to start with, so they always look a bit worn out. You don't want to be checking the air pressure AFTER a ride when the tire is warm, do it before. Enjoy that Wide Glide:rider
  7. glyd-n

    glyd-n Junior Member

    The rotor is supposed to be hot. The rotor helps dissipate the heat caused by the friction material of the brake pad. This is normal operation. The others have you covered, if the wheel spins with a light drag I would not be concerned, however if it does not, there is a problem which could be caliper related where the slides are binding or the hydraulics could be holding pressure.
  8. SixPak

    SixPak Junior Member

    re: 'front wasn't as warm as the rear either'. Do you use rear brake more than front? that might also cause a warmer rear rotor.
  9. TQuentin1

    TQuentin1 Well-Known Member Staff Member Moderator

    The guys have got you covered above. The pads are in light contact with the rotor in a normal condition, and hard when you brake with the rear. This friction causes hear. Plus, I think your heaters are right there next to the rotor. Your pipes will help to make the rear rotor hotter than the fronts. Additionally, the fronts are out there in the clean, cool air whereas your rear rotor is in the hot waste air from the engine and pipes.

  10. fin_676

    fin_676 Experienced Member Staff Member Moderator Contributor

    As i was taught to ride many years ago was taught to use the rear brake more than the front for general slowing of the bike front used for rapid deceleration so mine is always hotter than the front it is also shielded from the airflow by the rest of the bike any airflow that gets to the rear disk has been heated by the engine gearbox and exhaust system SO for me id say pretty normal
    if the pads had been dragging then the brake disc would be very hot and would give you a serious burn if touched