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Rear brake pads, clearance?

Discussion in 'Technical and Troubleshooting Torque' started by PhilC, Jun 21, 2009.

  1. I had my bike serviced a little while ago, and a day after that I had a flat rear tyre.

    When it was serviced they replaced the rear brake pads and told me to take it easy on them for the first 100k or so until they bed in.

    Shortly after the tyre repair I noticed a little squeaking when applying the rear brakes and there is a very mild rubbing of disk on pad with no brake pressure applied. I cleaned the disk and pads off with brake cleaner and that stops it for a while, but the squeak returns.

    A few rides ago I noticed the rear disk was hot to the touch when I hadn't been riding long or been riding the brakes.

    I'm working on the theory that either with the replacement, or with the wheel removal for tyre repair, that the brake pads were set in such a way as to lightly rub on the disk and in doing so are throwing off dust whilst riding. I think this dust is then giving me my squeak.

    So - questions:

    Is my working theory sounding right?

    Is there a simple adjustment that will allow me to increase the clearance betwixt disk and pad, alleviating my issue?

    Is it possible / likely that this rubbing has "glazed" my new brake pads leaving me with a brake squeak that will only be alleviated with disc machining and pad replacement?

    Or, given they're new pads, if they're glazed (how easy is this to see?), can they be buffed up with something to take the glaze off them?

    (I may just take the bike back to where I got it serviced and ask them, but I'd like to know, and besides, the solar panels aren't functioning with all this rain.)
  2. new brake pads do slightly touch, generally because disc sizes are different and pads arent strickly exact same thickness. gently wear off some pad, and it shoudl go away. squeaky noise is probs the material that has yet to wear off.

    you could just be resting your foot on the rear brake, the just ever so slight touch could be braking, as before your old pads wernt as thick, it didnt affect. ~ adjust free play

    or they fkd up somewhere n your brakes are always slightly on....

    my fronts used to squeak but ever since some good old wear from braking heavily from some NR rides its gone :LOL:
  3. If the replacement pads are the correct size, and the disc is in good condition, they shouldn't rub, However, if you lift the rear wheel off the ground and spin it, there will nearly always be some slight contact. This is normal. If the wheel doesn't spin pretty freely though, there is a problem.

    There is no way to adjust hydraulic brakes pads away from the disc. When you take the pressure off the brake lever, the pads are pushed back by the spinning disc. This is essential, otherwise the pads will be too far away from the disc the next time you apply the brakes, and you would have to pump them to get any braking effect. The clearance between the pads and the disc needs to be small, which is why warped discs are such a problem.

    If the pads are oversize (too thick) then they may indeed rub, since they can't contract back away from the disc enough, before hitting the limits of their travel. If this were the case though, the pads would have been hard to install. Sometimes though dirty brake calipers can mean that the brake cylinders wont retract fully, which will mean new pads will rub. Since you have cleaned the brakes, I assume this isn't a problem.

    If the disc is warped, then the pads will probably rub, but it will be intermittent, and should match the wheel rotation.

    Squeaking brakes can be lots of things, but if the pads are new, the most likely cause is that the pads have not been bedded in properly. Dust doesn't usually stay between the pads and disc on motorcycles, so that shouldn't be causing the squeaks.

    The best way to bed in brakes is described all over the internet, and often differently, but the general consensus is that a few well planned and executed hard braking efforts at long enough intervals not to overheat the brakes, which would cause glazing of the pads. Using new pads too gingerly is also bad for them, and can result in a bit of "polishing". Search around for the full procedure.

    If the pads are glazed, but not badly, they can be pulled out and sanded with some sand paper, and then re-bedded in. It's unlikely that you have badly glazed them over a short period.

    If the brakes are getting hot even when you haven't being using them, then you could be leaving your foot lightly on the pedal, and hence lightly applying the brake. A much worse cause though is if someone has adjusted the foot pedal up for you, and gone too far, so that the piston in the brake cylinder never comes back far enough to open the fluid return port. This results in a "pumping up" of the brake each time you use it, until it is constantly on. This has resulted in burnt, melted brakes, and even a couple of fires on my model bike. So if you, or anyone else adjusted the pedal up so that you can get on the brakes easier, you may want to reverse that adjustment immediately.

    Also check that the rear wheel was correctly fitted, the chain is properly aligned and so on. A problem here shouldn't be the direct cause of squealing brakes, but it may be causing some twisting of the disc.

    Bottom line: If nothing else is wrong, break the pads in properly and the squealing should go away.
  4. Everyone should read this, including a few "mechanics". Your brakes are there to stop you in an emergency and emergencies happen just as easily when your brakes are nice and new. So travel as carefully as possible and find a quiet road, then get your pads up to the task.

    Your brakes might last a few days longer if you treat them nicely at the start, but you might not.
  5. +1
  6. Thanks guys, good info and I'll go do some further reading.

    The brake pedal hasn't been adjusted as far as I'm aware (not by me and it doesn't seem any different). I'm also 99.9% certain I don't rest my foot on the brake in the course of general riding.

    They don't seem to "pump up" and the wheel does spin OK when on the centre stand. I think it's likely that I just haven't bedded them in properly, so I'll explore that.


  7. Agree to bedding them in before you go out in to heavy traffic but not to hard stops, best way IMO (tried and tested on many cars when i was replacing shoes and pads for years) is to do some varied speed stops starting smallish 40 to a gentle stop then gradualy stop harder, this way your not putting excess pressure on the part of the pad that has to be bed in (the bit thats sticking out further) and risk cracking it so it falls apart a few months down the track (does happen and the damage is enough to cost you new rotors).