Hi, The left front disk on my 3ln is giving this problem. As I leave the brake lever, the disk is not fully released and the brake lather keeps in contact with the disk. How can I fix this?
Assuming your disk isn't warped, your pistons aren't retracting, most likely due to being encrusted with crud. It's not a bad idea to do a full strip and rebuild of both calipers, but for those on a budget (time, money, skill), you can try a basic in-situ cleaning. Leaving the other caliper alone for now, pull the problem-child caliper and pads (DON'T disconnect the hoses). Spray the inner surfaces with brake cleaner, and wipe down. CAREFULLY squeeze the brake lever a LITTLE bit - you want to nudge the pistons out just a touch, not pop them out onto the driveway. With a nylon brush and brake cleaner, gently scrub the ring of crud off the polished piston surface (don't worry about the rough-cast inner surface and ends). At the same time, give a gentle scrub at the contacting surface of the dust boots. Once the pistons are pretty, push them back into their bores - you may need to use a piece of wood board. (You may need to crack your bleed screw - be VERY careful about getting air in or fluid onto paint! A length of appropriate-size clear tubing from the local hardware store over the bleed screw helps avoid both problems.) Once the pistons are retracted, use a small (glasses-size) screwdriver or dental pick to pull your dust boots, and clean some more in the bores. Do NOT disturb the inner seals unless you're replacing them! Replace dust boots, pads, and caliper. Squeeze the brake lever a few times to re-seat the pads; depending on how much fluid squirted out if you had to crack the bleed screw, you may need to top up your brake fluid reservoir. (Actually, this is probably a good time to flush and replace your fluid - if the pistons are filthy to the point of hanging up, the system hasn't been maintained in a LONG time.) If you have time and motivation, the other caliper is probably due for the same treatment. Obviously, if you do both calipers, do a flush and fill AFTER the second side is cleaned! <!-- s --><img src="{SMILIES_PATH}/icon_biggrin.gif" alt="" title="Very Happy" /><!-- s --> This sounds like a bit of work, but it isn't really that hard - have a friend over to chat, hand you tools and a beer, and it goes pretty quickly. The situation as you describe it is DANGEROUS. Your pads are dragging, and heating up. Far beyond the wasted gas and extra wear on the pads and disk, there is a very good chance the fluid will overheat, expand, and LOCK your front wheel while you're bombing down the highway!! <!-- s:shock: --><img src="{SMILIES_PATH}/icon_eek.gif" alt=":shock:" title="Shocked" /><!-- s:shock: --> <!-- s:-? --><img src="{SMILIES_PATH}/icon_Eyecrazy.gif" alt=":-?" title="Eye Crazy" /><!-- s:-? --> Good luck!
While talking about changing brake fluid, this is a regular job that should be done ever 3-4 years (normal road use). The brake fluid is VERY hygroscopic, which means it ATTRACTS water, even directly though the rubber hoses, etc. However this is not bad to a point because it can contain a certain amount before it starts causing corrosion in the brake cylinders, etc. The down side is that the more moisture, the lower the boiling point of the brake fluid. Once brake fluid reaches boiling, your brakes no longer will work as you can't get any pressure on the pads when you pull the lever.
Yup. I think most street bike manuals call for it every 24 months. Most racers change their fluid every season, if not twice a season - and after EVERY rain weekend. Few things are more annoying than the lever coming back to the bar while approaching the end of the back straight...
