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[mrgreen]

as above, my brakes have decided to do the dirty and i just want to try and sure myself up before spending the money!,
symptoms are:

1 pedal travels to within one inch of the floor
2. hardly any braking power, if i stand on them literally the front corner will lock up
3. pedal feels very spongey and doesn't pump up like there is air in the system.

 I think it's the master cylinder but just need any other ideas before i spend the money, frondt disks and pads were done maybe six monthsa ago.

thanks.

[tidla]

Are you losing any brake fluid?

Try clamping the flexi hoses to try and diagnose which brake circuit might be a fault .

[mrgreen]

it seems to have lost a little fluid but i can't see where from.

[dbug]

Try bleeding all old fluid out and replacing with new

[Nick W]

it seems to have lost a little fluid but i can't see where from.

That, and all the other symptoms are classic master-cylinder failure.
If you've no obvious external brake fluid leaks, then it will be leaking into the servo.

It might be worth undoing the master-cylinder mounting bolts and seeing if you can move it enough to see into the servo to confirm this, before buying a new one. I'd be reasonably confident about buying a new cylinder without doing this.

[Martian]

+1 for the master cylinder

[feeutfo]

it seems to have lost a little fluid but i can't see where from.

That, and all the other symptoms are classic master-cylinder failure.
If you've no obvious external brake fluid leaks, then it will be leaking into the servo.

It might be worth undoing the master-cylinder mounting bolts and seeing if you can move it enough to see into the servo to confirm this, before buying a new one. I'd be reasonably confident about buying a new cylinder without doing this.

Is it worth checking the servo pipe is fully connected and air tight.

And just wondering if the low level could be dropping naturally due to pad wear? Or is it  more than that proportionately?

[mrgreen]

it seems to have lost a little fluid but i can't see where from.

That, and all the other symptoms are classic master-cylinder failure.
If you've no obvious external brake fluid leaks, then it will be leaking into the servo.

It might be worth undoing the master-cylinder mounting bolts and seeing if you can move it enough to see into the servo to confirm this, before buying a new one. I'd be reasonably confident about buying a new cylinder without doing this.

Is it worth checking the servo pipe is fully connected and air tight.

And just wondering if the low level could be dropping naturally due to pad wear? Or is it  more than that proportionately?

#
servo pipes seem fine, with the motor off the brakes will pump hard once the vacuum is used, the level seems to have dropped about a third, I don't know how proportionate that is? anyway i have another master cylinder now just need the time to do it!! probably won't be before next week now, will let you know how it goes! thanks for the replies.

[feeutfo]

it seems to have lost a little fluid but i can't see where from.

That, and all the other symptoms are classic master-cylinder failure.
If you've no obvious external brake fluid leaks, then it will be leaking into the servo.

It might be worth undoing the master-cylinder mounting bolts and seeing if you can move it enough to see into the servo to confirm this, before buying a new one. I'd be reasonably confident about buying a new cylinder without doing this.

Is it worth checking the servo pipe is fully connected and air tight.

And just wondering if the low level could be dropping naturally due to pad wear? Or is it  more than that proportionately?

#
servo pipes seem fine, with the motor off the brakes will pump hard once the vacuum is used, the level seems to have dropped about a third, I don't know how proportionate that is? anyway i have another master cylinder now just need the time to do it!! probably won't be before next week now, will let you know how it goes! thanks for the replies.

the proof would be if new pads where fitted, the level would return to where it was. If you see what I mean...?

The level drops as the pads wear.

[Martian]

If I've read the OP correctly Chris, this is actual brake pedal travel they are referring to as opposed to brake fluid level dropping, in which case there is a leak in the system somewhere.
If the servo hose had failed, the pedal would feel rock solid and you need legs like tree trunks to get any kind of stopping effort out of them.

As the MIG is disc all round, we can rule out a leaky slave cylinder (which would also produce the symptoms described) so that only leaves the master cylinder.
If there are no signs of fluid loss from the back of the master cylinder when it is removed from the servo, it will be the seals inside on the piston that have failed.

[mrgreen]

thanks guys got the master cylinder fitted and all is well again! thanks for all the help