front Disc brakes no pressure

[shammon]

started to re assemble the brakes as no pressure when went to bleed them again on my Yamaha xj600 pre divy, Firts prob was bleed valves were blocked, then dirt in the resiviour, after cleaning and new pads....no pressure at all in handle.'

Master cylnder workes removed it and pressure from piston.
pipes free of debri etc., inc connection holes.
re assembled air bled and again no pressure again no leaks, then noticed no bite at all at the pistons or pressure on the pads so calipers pistons seized. what i need to know

1 is this what happens when the calipers on both sides seize
2 how the hell do i get them out to renew seals if i cant get pressure to pop them?
3 I would have thought there would be some pressure in the system still but no so could the master cylnder not be able to give enough pressure?
Cheers.
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YAMAHA YZF 1000cc THUNDERACE- 'ƃuıןןǝds ʇnoqɐ ʇıɥs ɐ ǝʌıƃ ʇuop ı

[Bezzer]

You'd get resistance from the lever if the pistons were sticking and not moving, could be the master cylinder wants new seals, air/fluid getting past it instead of pushing it out.
But sometime brakes can be a real pig to bleed and get the pressure up, if you haven't got a power type bleeder to give it a proper go then loosen the top of the reservoir, pull the brake lever fully on and cable tie it or similar to the grip. Leave it like that overnight and in a lot of cases any trapped air will rise and come out at the reservoir. If you can make the run as vertical as you can, drop the calipers and suspend them so the bango is right at the top to ease the air's passage, same at the reservoir, angle it so the banjo is pointing down as much as you can.
When you've done that put everything back as normal and bleed it again, if you're getting no pressure after that then it's pound to pinch it's the master cylinder.
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I used to be indecisive but now I'm not quite so sure.

[shammon]

Thanks.
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YAMAHA YZF 1000cc THUNDERACE- 'ƃuıןןǝds ʇnoqɐ ʇıɥs ɐ ǝʌıƃ ʇuop ı

[Kickstart]

Hi

As above. But a few other things to try.

You can use a large syringe to push fluid in through the bleed nipple (filling the system from the bottom). Can be messy though.

Also take the reservior cap off. Now pull the lever slightly. Often you will see some bubbles come up through the fluid. Release and repeat. Often only needs a tiny amount of lever movement (and pulling the lever fully tends to force the air into the system so you have to wait for it to rise up again). You can also tap the brake lines to encourage the air to the top.

Lastly wrap a cloth around the top banjo and put a spanner in place on it. Pull the lever hard and then crack off the top banjo and then do it up again before releasing the lever. Often the banjo is the highest part of the system and air bubbles tend to get stuck there.

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[shammon]

Just an update on how it was sorted

Force fed fluid through the bleed nipple up to expel air

Pushed back pistons fully to dispel air then re fitted and bled system again

Finaly the brake handle pin which pushes the master cylnder plunger in had to be re adjusted this is where most of the lack of pressure was comming from, often shows you how simple things sort that big prob.

Andy
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YAMAHA YZF 1000cc THUNDERACE- 'ƃuıןןǝds ʇnoqɐ ʇıɥs ɐ ǝʌıƃ ʇuop ı