New slave and master and still pedal loses pressure

[scotshaggis]

2017 Skoda Octavia Mk3 48000 miles. I replaced the (external) slave a week or two ago and a garage replaced the master cylinder today.

Very frustrating this. In the past it was fine for a long while after occasional pedal pressure loss. Worse recently, hence trying to address it. No fluid loss.

The garage is now closed until the new year. I bled the system with an eazibleed after changing the slave cylinder.

Should I try bleeding the cluth really well again? I was told today any bits of air actually ought not to cause a major issue, as they work their way to the slave (?). And obviously the garage (like I did..) will have bled it today.

If an O ring at a fitting was an issue, surely you'd get a leak?

Any advice appreciated. Thx

[No ideas for a name]

Is the slave cyl output moving when you press the pedal?
Just wondering if it is actually a clutch issue.

[spookly]

Hose expanding somewhere?

[scotshaggis]

Thanks for the suggestions. I think there’s only one small section of thinish flexible hose that goes to the slave cylinder and it certainly looked fine.

I’ve no reason to think it’s not just hydraulic. The pedal feel feels a bit on the soft side, then going extra soft when playing up.

[9xxNick]

Brake fluid can leak into the servo with no external leaks visible. Do you get any white smoke from the exhaust when the pedal has gone soft? Brake fluid being drawn into the engine makes white smoke.

[Grenadier_45]

I can see that being very frustrating.

Can you get a blanking cap onto the pipe going to the slave? Or even blank the output from the master cylinder if that’s easier to get at? Essentially I’d be wanting to isolate master from slave and see what happened. If the pedal is then firm it’s the slave, if not, the problem is between pedal, any linkage, and the master .

[350Matt]

I'd say to vacuum bleed it if you can, and also check the master cylinder isn't pre-loading the cylinder

if its not allowed to fully return back to the stop this can give issues

[bearman68]

I've had the anti bounce valve in the line give trouble before now - though that was in an Astra.

[scotshaggis]

Thanks for the replies. I still had bother after new master cylinder fitted but I think (hope..) it’s settled down now.

It was suggested I bled it by attaching a tube to the bleed nipple on the slave (pipe to height of the fluid reservoir) and let it bleed to the atmosphere, leaving it overnight. This seems to have worked quite well.

I’m still hoping it’s actually fixed now though. This being with the slave and master replaced.

[illmonkey]

scotshaggis said:

Thanks for the replies. I still had bother after new master cylinder fitted but I think (hope..) it’s settled down now.

It was suggested I bled it by attaching a tube to the bleed nipple on the slave (pipe to height of the fluid reservoir) and let it bleed to the atmosphere, leaving it overnight. This seems to have worked quite well.

I’m still hoping it’s actually fixed now though. This being with the slave and master replaced.

A reverse bleed, I had to do the same on my car after swapping both. I used pressure, rather than leaving it overnight and it sorted it right out.

[GreenV8S]

If the problem comes back, can you describe the symptoms a bit more clearly? Your mention of 'going extra soft when playing up' seems to suggest it's an intermittent problem.

[scotshaggis]

Months and months ago it lost pressure one day but then for (six?) months it was fine.

Then same again. One day the pedal lost pressure. Subsequently it happened more often after that. I then then changed the slave and bled it with an ezibleed. It was maybe not bled well enough, I’m not sure, but a week on the pedal lost pressure again.

I’d bought a master cylinder too so I got a local garage to fit it hoping for an end to the problems. But no, it was worse! But I think it was full of air.

I think and hope (still can’t be certain until more time elapses) but I feel it might be ok now after I bled it overnight.