Welcome to Netrider ... Connecting Riders!

Interested in talking motorbikes with a terrific community of riders?
Signup (it's quick and free) to join the discussions and access the full suite of tools and information that Netrider has to offer.

Spongy brakes

Discussion in 'Technical and Troubleshooting Torque' started by tonee, Feb 8, 2011.

  1. This morning i forgot to take off my rear disk lock and started rolling. After removing it and riding the brakes were spongy at speed. If I hold the pedal down I could feel a pulse under the feet. The breaks would start to engage as I'm rolling to a stop or stationary.

    I've tried bleeding the line and still nothing.
    Can someone please help me out


  2. pulsing brake = warped rotor
    spongey brakes could be air in line, water in fluid or a seal somewhere said goodnight
  3. Not to sound like an ass, but are you sure you bled them right? Was there much air in the lines when you bled them?
    I would also be checking everything else.
    As above if pulsing rotor probably warped.

    Have you given the calipers and rotors a proper clean?
  4. I was told to pump the brakes and compress them as hard as I can, then undo the air nipple nut as air/fluid comes out(correct me if im wrong).
    The strange thing is the brakes work like normal when im just pushing it back and forth at a stand still but when it's going at speed eg. 60km/hr the pedals goes all the way down as though theres no compressed fluid and pulses.
    Even if its warped, the pads would still press on the rotars and i'd still have feedback from the pegs?
  5. The warped rotor could be pushing the brake pads back - which would explain why it's firm when standing still but loses pressure when rolling.

    I'm having a similar problem with my bike at the moment except I don't get any pulsing - have to wait until I can get it up on a front stand to check if it's a warped rotor or not.
  6. Did the disk lock hit the caliper when you moved it?

    Sounds like a warped rotor, get it up on a stand & give the wheel a spin, see if you can see the rotor move in & out as it spins.

    If so, replace.

    If not, try another bleed.
  7. The calliper on these GSXRs are on the bottom so it didnt touch it at all

    If its warped, can I resurface it like how you do it with car rotars?
  8. this is right but in the OPs case it may be the disc is just sitting a bit askew in the float spools.

    Get the front wheel off the ground and give it a spin. Have a good look at the spools. You may be lucky in that you can tap it back in with your shoe or a rubber mallet.

    If it is warped, however, you can't machine bike rotors. They are just too think to start with.

    Also are they Tokico brakes? These have a problem that I'll expand on if the above isn't the problem
  9. Just chucked the rear wheel up and had a look where friction was at most. Started taping it with a hammer and cloth. So far so good as the pulse intensity reduces, just needs a couple more taps at the right spots and its all good again
  10. If you're still having trouble with it, send me a pm, we can take a look at it tonight or even tomorrow night before the PMR.
  11. Yeah im still having trouble...kind of gave up and rang race rep to a quote of $199 ](*,)

    If you think you can shine some light tonight it would be great =]
  12. Should be free tonight, I'll check with the missus & let you know.
  13. Thanks!
  14. Pm sent.
  15. MV helped me bleed the brakes again and now its not spongy anymore, however we've concluded the rotors are warped.

    Is there any difference between a $55 and $190 rotor? Do prices reflect on some sort of quality or are they all simple a piece of steel.

    I found this on ebay from Australia

    Also this that's from asia which looks pretty much exactly the same to me...

    Or should I go to the wreckers and pick up another one for 100bux
  16. Same thing with me - my front right rotor is warped :(

    More expensive rotors are heat treated and better made so they'll withstand greater braking force. I've read some cases of ebay rotors cracking/warping under pressure.

    On a sportbike the majority of braking is done with the front rotors - so in your case, there's no problem getting an ebay rear rotor because it's unlikely that you'll be using it enough to damage it.
  17. A neighbour bought a zzr1100 with new ebay rotors on it, He took it in for the roadworthy to transfer reg and was told the new discs are undersize and needed to be replaced.
    SO - be careful with what youre betting your life on..