front brake rubbing problem

[pingpong]

Hi all,
I think my front brake pads are rubbing on the rotor. Before, it wasn't very noticeable, just a light squeaking noise occasionally, so I didn't give it too much of a thought. Just today, though, the squeaky rubbing noise was louder and totally noticeable, almost like a scrapping sound, but disappears when I apply the front brake. Also, I realized that pushing the bike is more difficult, so something is definitely up with the front brake. There's also a light circular ring about 0.5 inches from the outside edge of the rotor, so I'm guessing that's where the rubbing is happening? I don't think my rotor is warped because I don't feel any pulsing, so what could it be? I recently took the bike to a shop to get the tires changed, could something have happened when they put the wheel back on the bike?

[ledfingers]

look at your pads. they're probably worn all the way down. if you've got a deep groove in the rotor, replace it, don't take chances with brakes.

[Turd Ferguson]

Yup, sounds like it could be warn down pads.  If the ring in the rotor is of any noticeable depth, you need a new rotor as well as pads.  Get down there and inspect it before your next ride.  Brakes are serious business!

-T.

[The Buddha]

Some Scraping sound is normal.
Lever pulsing is not a common occurance with a warped rotor. Pulsing is a symptom of a rotor defect where it has thick and thin spots. Not like a car rotor.
Deeply grooved or super thin (under 4mm is it) rotors are bad. The piston is well out of its use range especially if pads are worn too.
Your problem may be that the rotor is thin or that the pads are worn ... or the pivots need to be lubed ... or its normal.
Cool.
Srinath.

[pingpong]

OK, so I took out the pads today to check them out, and they seemed to still have some life left. I noticed, though, that when I pumped the brakes without the pads in, only the larger piston would move out. The smaller one was just stuck there, which I guess is what caused the problem with the scrapping. Also, even with the cover for the master cylinder off, it was hard as hell to push the piston back into the caliper. I figured there's probably a bunch of dirt or whatever in both of the piston bores, so I ended up just taking the whole caliper off and, when cleaning it, noticed a crapload of gooey gunky stuff in the smaller piston bore. No idea what it could be. I also noticed some brake fluid dripping along the brake line, so I figure I have a leak on the hose too. Where would I be able to find a rebuild kit for the front brake caliper? Also, if i were to have a shop do the job of rebuilding the caliper and setting the bike back up, how much should I expect to pay?

[The Buddha]

Fluid dripping down the brake line ... make sure it doesn't hit paint. It will eat paint.
Now you managed to tear a seal in the caliper I thing ... or pushed the pistons back in without opening up the top in the master cylinder didn't ya ... Pistons are hard to push back. they have a huge mechanical advantage you are trying to push against. Cleaning it is great, but you almost need to clean and lube what you see on the outer side of the piston and then worry about shoving it in ...
I'd reseal the caliper, then fill and bleed the system with dot 5 fluid. You already have air in the system I'll bet. 5 brake fluid will not eat paint. Its silicone based and it can lube the vacuum pump too.
Cool.
Srinath.

[pingpong]

This is a noob question, but what level is the fluid in the reservoir window supposed to be at? Should it be higher or lower than the line that says "Lower". I was really confused by it because I didn't know if it meant that the fluid should be lower than that line, or if the line is for the lower limit of how much brake fluid I should have.

[pingpong]

Nevermind, now that I think about it, that was probably one of the stupidest question's I've ever asked. In any case, I finished rebuilding my caliper and added a SS brake line. I bled the reservoir as per the Clymer manual, but I can't seem to get any fluid through the brake line. I had the bleed valve open, and pumped like mad for about 10 minutes, but fluid just wouldn't feed down. Do I need to start sucking on the tube from the bleed valve while I pump or something?

[The Buddha]

Sucking it from the bleed fitting is good use the vaccum pump if you have it, you may be OK with just opening the bleed screw and pumping it ... you're air locked right now ... common problem. You need the air to go somewhere. If you're using Dot 5 you can handle it with a lot less care. It wont eat paint and lubricate the vacuum pump at the same time.
Cool.
Srinath.

[pingpong]

How much pressure would the pump need to produce? If it's not that much, could I just create a vacuum using my mouth (is that even safe)? I'm low on funds right now so I'd rather not have to go out and get a vacuum pump.

[Jughead]

First Pump the Handle,Hold and then Break the Bleeder..Let go,Pump the Lever,Hold,Break the Bleeder.Repeat a bunch of Times. If your Brake was Dragging your Hose may be Collapsed or it's Possible that your Piston in your Caliper may have a bad spot and it could be Holding instead of Returning to where it Suppose to be.It could Also be Cocked Slightly in the Bore.

[pingpong]

Urgh, so after getting new seals and cleaning the caliper, the pistons still stick (one of them doesn't retract). Guess either my pistons or piston bores are shot, so I'm guessing a new caliper is in order? The pistons and bores looked fine when I cleaned them, so I don't know what the problem could be.

Also, I'm just wondering, what exactly allows the pistons to retract when you release the brakes?

[Flywheel]

You should be able to get a real cheap ($1) brake bleeder hose with a drip-valve tip, so don't try and use your mouth to siphon something that poisonous. The real trick, as I found out after some experimentation, is to ensure the container you are bleeding into is HIGHER than the brake caliper. Otherwise, not enough pressure is generated to bleed the bubbles and old fluid out. Open the bleeder bolt, pump the brake, hold, close the bleeder bolt, release the brake, repeat. Works like a charm.

[pingpong]

You should be able to get a real cheap ($1) brake bleeder hose with a drip-valve tip, so don't try and use your mouth to siphon something that poisonous. The real trick, as I found out after some experimentation, is to ensure the container you are bleeding into is HIGHER than the brake caliper. Otherwise, not enough pressure is generated to bleed the bubbles and old fluid out. Open the bleeder bolt, pump the brake, hold, close the bleeder bolt, release the brake, repeat. Works like a charm.

Yea I ended up just getting one of those Acton vacuum pumps, so that's not a problem anymore. Now it's just that the slave piston is still sticking. Both seem normal, so is it possible that for some reason there's less resistance on the master piston, so it gets forced out while the slave piston doesn't?

[pingpong]

As an update:

I took apart the caliper again today and cleaned the bores and pistons until they wear spit shiny. Put them back in, lo-and-behold, they still have issues. Both pistons "work", but when I pump the brakes without the pads in it, sometimes the slave piston will move, sometimes the master piston will move, and sometimes both will move. Sometimes the pistons move very smoothly, sometimes they kind of pop, and sometimes they recess. This, mind you, is after the brakes have been completely bled. Yea....I think I'm going to give up on this caliper and just install a new (well, new to me) one on the bike.

[pingpong]

O, and just out of curiosity:

Clymer says that to realign the pistons, you gotta spin the wheel while applying the brakes. What exactly does spinning the wheel do?