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.

Pulsating front and rear brakes

Discussion in 'Technical and Troubleshooting Torque' started by nightgash, Sep 5, 2007.

  1. My rear brake is really pulsating and my front is pulsating and squeaking. This is very noticeable at slow speed like pulling up at the lights.

    I have been doing a few emergency stops lately and was wondering have I overheated my disks and caused them to warp? I hope not because it will be so expensive and hard to replace... :(

    Or could it be the pads are gone and are causing this? What about the brake fluid could it be old and need changing? Bike is a 93 FZR250 has dual front disks and a single rear disk brake.

    :cry: :cry:
  2. Your disks rotors are probably warped and below minimum thickness. You need a micrometer or vernier caliper to measure there thickness.
    Look on the rotor carrier, somewhere it will say min thick, or min dia or similar. As you know- Very expensive to replace unfortunately :?
  3. I fear Ken is right; it sounds very much like warped discs to me.

    You MAY be able to score second-hand replacements at a wrecker, if you're lucky.
  4. Could heavy braking warp them by overheating them? I mean 5 emergency stops from 100 km/h in succession?
  5. I dont know about that, when you are braking slowly does it feel like they are pulsating at the same point on the rotor (like riding a pushbike with a bump in the tube)?
  6. It just feels like its grabbing and then letting go. The front brakes are squeaking and going on-off-on-off very fast but the back one feels as though its only happening once every wheel revolution. :(
  7. It sounds like warped rotors but you should get someone to check you wouldnt want to buy them and find out it was something else :)

    Also you might want to go for aftermarket rotors it may work out cheaper than OEM ones.
  8. Maybe I should just live with it! I mean you only need your brakes for stopping! :LOL: :twisted:

    Nah its only really noticeable at low speed especially the rear brake. I'm going to take everything apart and see whats going on.
  9. Wear and tear I'm afraid. Don't worry, all discs either go thin or develop a warp, you can't really stop it without going overkill in the thickness department... and then they would still need honing occasionally.

    (did the patol's discs the other day - had developed a .7 - 1 mil runout from a 0 runout over 3 years(limit is .6 or so, if I remember)

    I remember reading somewhere that (if you havent overheated them)it's like the same way corrigated roads happen - it all starts from a single miniscule bump, and goes downhill with time. (the bump artifically raises the disc, causing uneven wear.)
    Dunno about the accuracy of that statement, but it seems logical to an extent.
    Thermal fluctuations - I.e. normal stop-start-hot-cold would contribute. Lot of kinetic energy that needs to be converted to friction.
  10. I gots that pulsating thing going on to for months now - but it only happens when I do a really long brake (from a high speed realising that I can't make the yellow light) then it starts to pulsate.

    so it doesn't happen that often - just it situations where the brakes are overused at one given time,
  11. What happens when a brake pad gets to its minimum wear mark? Does it cause pulsating? I'm starting to think I have a brake pad that needs replacing on the front and the rear disc is warped...
  12. No brake pads dont cause pulsing. It is caused by an imperfection in the disk surface either lateral runout (side to side), variation in disk thickness (unlikely in a used disk) or localised surface imperfection (can be caused by parking a vehicle with a hot disk - generally only racing can get things this hot).
    The road rut theory proposed earlier is crap.
  13. Yup , this can lead to warping or 'hot spots' on the rotor, with symptoms just as you describe.

    Im too new to the bike scene to know if its the same process, but normally for a car you would go to a brake workshop and get them machined or you can get a mobile brake machining guy that comes to you.
  14. You replace the pads, thats what the min wear mark is for. After that you are living on borrowed time as the pad wont perform to standard.

    As for disk warpage due to 5 repeated stops from 100K, very very unlikely. What do you think happens when racing or doing track days?
    If however the disk is at or below the min thickness specified anything could happen. Once brakes get below the manufacturers min specs the brakes basically wont be performing to the required standard in all situations, in particular if given a work out.

    Pulsing brakes (depending on degree) can be dangerous as the braking force through the tire is uneven and increases the likelyhood of skidding under brakes, especially in the wet.

    Yes disks are expensive but what ie your and those around you lives worth.
  15. The thing that causes most disc warpage is stopping and parking with hot brakes. The disc cools down quickly except for the part that is covered by the caliper. This is why clever racers don't use the brakes much on a slowdown lap.
  16. Thanks for all your help. I checked the pads and all were not down to the wear indicators. I changed the rear brake fluid out for new stuff and lubricated the points on the floating disks on the front. Also gave the rotors a light sanding with 1000 sandpaper to remove any scum but it looked pretty clean.

    Maybe the rear brake was always like this since I bought it because I never really used it much? :(

    Thanks for everyones help!