Pop Up Front callipers staying on after Pad change?

[PopKat]

As stated I've put a new set of 4 pads on and pushed back the pistons taking out some fluid from the reservior.
I now have a very short lever pull and when I release the lever tha brakes are binding still. I firstly stopped and took a little more fluid out leaving a slight air gap under the rubber seal and that has improved things a little but they still seem to bind a little?
What I didn't do was undo the bleed nipples as I didn't want to snap em off if seized.

Have I broken something forcing the pistons back without undoing the bleed nipples?
Any ideas or will it just settle down when the pads bed in?
Cheers
Harvey

[callyboy]

How much are they binding Harvey ?

Pete

[PopKat]

Thanks, The Fluid was replaced quite recently from the clutch and brake reserviors but I'll maybe try and see if the bleed nipples will undo to flush the old stuff out of the callipers. There may be some sort of one way valve in the master cylinder that stops fluid coming back once its forced into the lines? I did have trouble forcing back the pistons on the second calliper due to it filling and pressurising the small reservior.
As I say since I let a bit more of fluid out of the reservior its certainly is better now but they still bind enough to heat up the discs and for me to feel the bike slowing a touch when coasting.
Maybe they'll sort themselves out after a few more runs out as I very rarely get the time for a ride nowadays to put some miles on the Kat.

[Katgeezer]

The fluid level should be a high (or low, I guess) enough for you to see a bubble in the sight glass. Any higher and you've to much fluid causing drag.
That might be stating the obvious to most people but not everyone is an experienced mechanic so I hope you don't think I'm taking the mick or anything.
You won't have damaged anything doing what you've done up to now, but if you ride to much with the brakes dragging you could warp your discs. Also you need to bleed the system thro' the bleed nipples to get any lingering air out.

[Russbusa]

If the pistons were not cleaned before you pushed them all the way back they are probably just too tight in the seals, if your changing for new pads after the old ones have been in for a long time hence exposing the pistons, its good practice to pump them out and clean them up. There is also usually some corroded aluminium around the seals in the grooves which makes them even tighter. A proper strip down and clean up should sort the problem. Or if needs be, remove the pads, pump out the pistons as far as you dare then give them a good clean before pushing back in.

There isnt a one way valve in the system as the brakes would not release - ever

The seals they are cheap and easy to replace, I have a friend who works for the local bmw car dealership and he says they often refit the old seals back into the cleaned calipers then went on to explain in depth the reason that this was not bad practice as long as the seals were undamaged.
When you apply the brake the piston moves out, when it can move no further the fluid presure pushes on the rubber seal thus deforming it and pressing it against the caliper and piston sides, it is this deformation that seals the system and not the physical fact the seals are just touching the caliper and piston. The higher the pressure the better the seal.

My hayabusa goes out no matter what the weather and I've had my 6 pots apart twice in since i've had it for the same problem.

[PopKat]

Ok, I did clean up the pistons but probably still have a little too much fluid in the system. No high level marked just a low one?
I'll have a play and see how it goes.
Cheers
Harvey

[fossie]

Thought I posted this yesterday. As Russ said, but i would add what pads have you fitted?
i ask because the front padson a pop up, are the same as rears from later suzuki FA63 and some have more kevelar ,type material.

[PopKat]

All seems fine now so suspect i just had too much fluid in the system initially?
Harvey