Binding disc brakes!! Please help.

[R65Singh]

Yesterday while riding my bike i noticed the motor straining while accelerating so when i got home i put the bike on center stand and  noticed that my front brakes are binding and the wheel does not spin freely.  
So today I took the calipers out, the pistons and everything else was moving freely and no binding at all so i replaced the brake fluid and put everything back together but the result is still the same.
When the brake is squeezed there is lot of pressure at the brake lever, it hardly moves.  So does that mean the master cylinder needs work?  Please correct me if i am wrong.....i think the pistons should move back when the brake lever is released letting go of the rotors, but i don't see that happening.  
Can there be anything else that is causing this?  Is there any return hole in the master cylinder that can get plugged or something?  Please help me out.  Thanks

[Barry]

Is there any return hole in the master cylinder that can get plugged or something?

When you were bleeding the brakes you should have seen a tiny hole at the bottom of the brake fluid reservoir. This might be blocked although I'm not sure how you would have bled the brakes successfully if it was.

.....i think the pistons should move back when the brake lever is released letting go of the rotors, but i don't see that happening.

If the pistons are moving freely It is normally possible to see them move just. You could try opening the bleed valve a little when they are binding and see if that frees them up up. If it does that will tell you the problem is in the master cylinder and not the caliper pistons.

[R65Singh]

That was very quick Berry...Thank you for the suggestion.  the passages in the calipers were clear but i will give it a shot to the second point you enlightened.  Thanks for the help!!

[Johnster]

Every time I've had a vehicle w/ sticking brakes, it was cured by-
remove calipers, pull out pistons, clean out, use 'crocus cloth' if necessary, make everything shiny.  Then reassemble and bleed.
  ususally its dirt on/around the pistons in the caliper.  if all you did was bleed them, the issue may or may not come back.

-John

[R65Singh]

John, thanks for your suggestion.  I did took every thing apart and cleaned the pistons.  Everything seems to in normal working order except that i did not had a chance to rebuild the master cylinder

This morning I did the test that Berry had suggested and sure enough there was some brake fluid that came out once i loosened the bleeding screw and there was less pressure on the pads but wheel was still not 100% free. I could still hear some touching of brake pads to rotors....may be that is normal...have no idea. So I guess I am on to checking the M cylinder out.  Kind of intimidated because don't know what to look for and have never done it.  Any things to watch out for while working with Master cylinder?

[Mike V]

Singh,

This same problem has happened to me in the past. I may be wrong, but it sounds like your return port may be partially blocked. As Barry has stated; if you look in the bottom of your master cylinder reservoir you'll find a very tiny port.  It doesn't take much for these to become blocked.  I take a single copper strand of electrical wire and carefully run it in and out of this little port. Hopefully if there is a blockage this will clear it enough for the fluid to flow unrestricted back into your reservoir relieving the pressure to your caliper when you release the brake lever. Be careful not to get brake fluid on any painted surface - it will strip the paint. I take a shop rag and tie it around the bar mounted reservoir to catch any spillage and cover my gas tank and front fender with a damp cloth or towel (just to be sure). Don't squeeze your brake lever too agressively as it may spit fluid where you don't want it.

[MrRiden]

Just to confirm Barrys advice, I have had the return port in the master cause the calipers to not retract. It is visible at the bottom of the reservoir, the smaller of two you should see. You may clear it only to find you are unable to build pressure in the system again. In my case a new master from MotoBins and a locally made brake line brought everything back to working order. good Luck and keep us posted.

[GrimReaper]

 You said that the pads still touch the disc.When you spin the wheel do you feel or  hear that touch?If its only a noise it is normal

[R65Singh]

Just to confirm Barrys advice, I have had the return port in the master cause the calipers to not retract. It is visible at the bottom of the reservoir, the smaller of two you should see. You may clear it only to find you are unable to build pressure in the system again. In my case a new master from MotoBins and a locally made brake line brought everything back to working order. good Luck and keep us posted.  

Today I opened up the cover of the brake fluid reservoir and noticed those two ports at the bottom but cant tell if they are blocked or not without inserting a wire or something in there which I am bit afraid to do that this might damage some seals on the plunger.  I don't want to make it worse than what it is.  In your case it sounds like it made it worse.  I would like to save the master cylinder and see if some repair fixes it.

[R65Singh]

You said that the pads still touch the disc.When you spin the wheel do you feel orhear that touch?If its only a noise it is normal  

Sincity_r65 I feel a bit resistance which is little bit more at one spot than the others and hear the "little pad grinding" noise as well.  Also I tried to look at the gap between the rotor and pads by shining a flash light and i see gap on only one side of the pads.   Does that mean that the wheel is not exactly in the middle or some shims are missing if it ever actually had a shim at the first place?

[Darwin_R65]

It's all meant to be self centering (to a small degree).

As for if it's centred, don't check the pads or pistons, check if it's roughly centred in the caliper housing.

There is a small passageway between the two sides, and fluid pressure will determine even pressure on both sides of the brake rotor. If only one side is progressing to the rotor, you either have a sticking piston, or a blocked passageway inside the caliper itself.

When you bled the brakes what colour was the fluid?

Over the years I have learnt the wisdom of changing brake fluid regularly to avoid gunk build up inside the calipers. (And learnt the hard way i might add)

John

[Adamastor]

Do you see any air bubble showing at the reservoir when you pump it without the cover (be careful with spills)?
I had front dragging brakes (only left side disc) and was caused by air in the system and a ridiculously small leak at the bleeding screw.
If you do have any bubble on the reservoir when pumping the brake lever you have found part of the problem...

Sergio

[donbmw]

Check brake hoses I have had one deteriorate inside and hold pressure on the brakes.

[R65Singh]

Well, finally the brakes are back to normal and the bike feels like it got 20 more horses in it.  
The problem was with the tiny plugged port in the master cylinder.  The port is so tiny that at first it looks like there is no through hole there.  There are two ports (holes)  there, one a large enough that chances of getting it plugged are slim,  the other one is so tiny that it is even hard to see if it is in there.  This tiny one was plugged so bad that soft copper wire won't buzz it so had to use a strand from the wire wheel (older brake cable strand probably a better bet).  I had to use a needle nose pliers to hold the wire and push it through the port with a bit of effort.  Once it was all cleaned and put back together with new brake fluid the wheel is running without any resistance.  
I am glad it worked out  and A BIG THANKS to the members of this forum.  The bike runs so much better and no more slipping out feeling while making turns.  

[Ed Miller]

Cool.  About how far in did you push the wire?  I've never had to do that, yet anyway.  (Knock on own head.)