brake master cylinder failing?

[Sam reid]

I have had a spongy brake pedal for a while now, so tonight I decided to flush the system.

Flushed all the fluid (which I doubt has ever been changed as it was cloudy as f**k) ...

But I still have the same spongy pedal

Is it probably the master cylinder that's gone?

 

[Matt10160]

I'd check all flexi pipes, one might be damaged/worn and expanding under pressure

 

[Sam reid]

I couldn't see anything worn or and damaged on my flexi's they looked in fairly good condition tbh

When I bled the line closest to the MC there was alot of air coming through

 

[92Lambie]

Bump*

Ive got the same thing, i had my fluid changed, and since then i have a spongy pedal... ive heard the seals could of rolled inside the master cylinder.. any news yours Sam?

 

[Sam reid]

Nah I've not really got much further with mine, probably gonna do the master at some point in the near future.

Was your pedal spongy before You had yours changed?

 

[92Lambie]

No it was fine mate, sharp and right at the top.
I put new pads and disks in the other week cos it needed them so now it's just the master to change.

 

[SootySport]

To test the M/C, press your foot on the brake pedal, if it slowly descends to the floor, it's ******. You may have to keep your foot on the pedal for a couple of minutes. This all providing you don't have any fluid leaks elsewhere in the braking system or one of the flexi hoses is ballooning.
If you had drained all the fluid so the fluid was below the M/C piston and pressed the brake pedal, this will cause the seals to roll over or just loose a good seal inside the M/C bore.

 

[Sam reid]

Do this with the engine running?

I bled the system with a pressure bleeder, so I doubt I rolled or damaged a seal unless it was like that before I started

 

[SootySport]

Engine off.

 

[92Lambie]

To test the M/C, press your foot on the brake pedal, if it slowly descends to the floor, it's ******. You may have to keep your foot on the pedal for a couple of minutes. This all providing you don't have any fluid leaks elsewhere in the braking system or one of the flexi hoses is ballooning.
If you had drained all the fluid so the fluid was below the M/C piston and pressed the brake pedal, this will cause the seals to roll over or just loose a good seal inside the M/C bore.

Soot1, when my engine is off, i can pump the pedal until its rock solid after a couple of pumps.. then as soon as the engine is switched on, it sinks all the way down..

 

[SootySport]

That's right, with the engine on the brake servo bleeds off air pressure with your foot constantly on the pedal although it shouldn't go all the way down to the floor. Should be reasonably hard with the engine off. Have you actually driven the car? it may be ok.

Was the handbrake ok before you started changing the fluid? if you have to pull it up a long way, then the cable will need adjusting, you'll then have less pedal travel.

 

[rizzini7]

Mines been doing a similar thing. Had braided hoses fitted so assume it shouldn't be them?
Also some times on startup I get an alarm and the handbrake light flashes then it's fine. It's not recording a fault anywhere either??