Hello,

Sorry if this is a tired topic, but I don't really understand it properly. I fell into the trap of consulting AI on it a lot back in May as it would give quick responses to all the details, and at the time it seemed like it was realistic and made sense, but really it doesn't seem to track.

So originally my MK1 Fabia had a hard pedal. After a wild goose chase with the servo and its vacuum pipe (which would have become a problem later anyway), we found that the actual cause was a blockage in the ABS pump causing 1 wheel to receive no brake fluid. So we replaced the ABS pump and the pedal was a lot softer and we had much better braking performance.

We bled the brakes a few times and replaced the front brake pads as my dad wanted to change them. Then we ended up bleeding them again as we noticed that the pedal was a bit soft. I don't remember at what point we first noticed this, and if any difference was made by the brake pads. It is possible that it was always that soft, but we didn't notice initially as we were expecting a much softer pedal after fixing the old hard pedal.

So my Uncle who is a car mechanic who we asked about it, insisted that the brakes were soft because of the new pads and I was just overblowing it because I'm a snowflake or whatever. But I can't see that it would make them that soft, and 1000 miles later the pads should be worn in but there isn't any difference.

So originally we assumed it was air in the system and we bled it a load more, but we don't know if there is air in the pump that can only be bled by doing a VCDS bleed. But surely the air trapped in the pump that a VCDS bleed would get out, would not be part of the normal braking hydraulic circuit, until ABS kicks in and extra valves open and the pump has to operate. Otherwise you would be able to bleed it normally and only have the braking dynamics change after an emergency stop where extra air is introduced to the normal circuit. But then I looked more into what I heard about how you are not supposed to use the full pedal travel when doing a 2 man bleed. My dad said he didn't think this was necessary as he had never had that problem with another car. So the AI ended up convincing me that I had damaged the master cylinder seals by bleeding it improperly, which I came to accept, but I haven't yet bought the parts for that job as I keep putting it off as I'm anxious about bleeding the clutch and that becoming a similarly long story. I have already determined which master cylinder and servo mounting gasket I need for that. I just haven't ordered anything.

So I've been driving it like this for about 1000 miles (admittedly a lot of them motorway/dual carriageway, but not exclusively) and it stops perfectly fine, just the pedal travel is obviously more than it is supposed to be. I've kind of got used to this now. My dad thinks it might fail its MOT, which is on Friday, for insufficient reserve pedal travel. So I've been told to get the new master cylinder ordered in case we need to change it for a re-test.

But today I am looking at other posts on this topic, and it sounds like when the master cylinder seals fail, this is normally accompanied by fluid leaking from the master cylinder either into the engine bay or into the servo. To my knowledge, neither of these have been occurring and the fluid level has not gone down significantly since we last messed with it. I would expect it to go down a bit due to the brakes bedding in. I need to check this again though in the light tomorrow. I hadn't been looking for leaks there before, only at the ABS pump unions.

So now I am wondering whether it is the seals after all, or is air in the system. How do I tell?

The brakes don't "pump up", which is why I didn't think it was air in the system. Instead, you get a bit of travel, then the pedal gets harder, then if you press on the pedal for a longer time, it very gradually sinks. You can only really do that if the engine is running and the servo is active. The pedal doesn't actually hit the floor, but I don't know if that is possible or if there is a stop somewhere that another part of the pedal hits, or in the MC. So that seems like the MC seals, but why then are you still able to get good braking pressure, and why is there no fluid loss?

The master cylinder is the 19 FTE 5615 one if it makes a difference. And the ABS pump is the mid range one that has ASR but not ESP, I think, though I can't remember exactly. Mine doesn't have the ASR button but I think that's because it's an '07 and you can't turn it off. It definitely isn't the ESP one though as we didn't need to do the steering angle calibration when we replaced it.

Sorry I've made this really long winded. I'm just trying to include as much information as possible that might be relevant.

Elliott

If the pedal gradually drops under pressure and there are no leaks and your sure theres no air in system its more than likely the seals that have gone on the brake master cylinder. The fluid is probably getting past the seals/bypassing but its not leaking. Daughters peugeot 205gti did exactly the same a few weeks ago. Brakes were a bit soft for a while and then virtually no brakes even if you pumped pedal.

Alasdair.

Meant to add on the peugeot 205 gti if you used a lot of force on brakes it gradually sunk to floor. Listen around the brake cylinder. On hers theres a high pitched sort of whine noise which I assume is the fluid under pressure getting past seals. Try with engine off and pump till hard if possible and then apply a good bit of force. We couldnt hear it over the engine.

Alasdair

I got air in my ABS unit once and I can confirm it causes a soft pedal. The pedal can be pumped hard with the engine off but would sink soft as soon as the engine was started. A little engine start sink is normal, an inch or so due to the servo, but I mean much more than that.

Normal brake bleeding won't help but a VCDS ABS bleed procedure immediately cured the issue.

You say you've refitted an ABS unit, I would not hesitate in saying you need to do the ABS bleed procedure on it. It is not only VCDS that can do that, many OBD scan tools can do ABS Brake Bleeding.

On 29/09/2026 at 10:58, Alasdair1 said:

If the pedal gradually drops under pressure and there are no leaks and your sure theres no air in system its more than likely the seals that have gone on the brake master cylinder. The fluid is probably getting past the seals/bypassing but its not leaking. Daughters peugeot 205gti did exactly the same a few weeks ago. Brakes were a bit soft for a while and then virtually no brakes even if you pumped pedal.

Alasdair.

On 29/09/2026 at 13:12, Alasdair1 said:

Meant to add on the peugeot 205 gti if you used a lot of force on brakes it gradually sunk to floor. Listen around the brake cylinder. On hers theres a high pitched sort of whine noise which I assume is the fluid under pressure getting past seals. Try with engine off and pump till hard if possible and then apply a good bit of force. We couldnt hear it over the engine.

Alasdair

Thanks for replying guys.

OK, so that can happen that way without fluid leaking from the system. That is good to know.

I'll have to try listening to the master cylinder while someone pushes on it. Though with this one I've never have it give absolutely no brakes. I don't think we can get much pedal movement without the servo though, even pushing hard.

19 hours ago, aubrey said:

I got air in my ABS unit once and I can confirm it causes a soft pedal. The pedal can be pumped hard with the engine off but would sink soft as soon as the engine was started. A little engine start sink is normal, an inch or so due to the servo, but I mean much more than that.

Normal brake bleeding won't help but a VCDS ABS bleed procedure immediately cured the issue.

You say you've refitted an ABS unit, I would not hesitate in saying you need to do the ABS bleed procedure on it. It is not only VCDS that can do that, many OBD scan tools can do ABS Brake Bleeding.

OK. That's interesting. Isn't the pumping hard with the engine off just depleting the servo vacuum though, nothing to do with compressing the air in the system by ramming more fluid in? There probably is air somewhere in the ABS pump, but won't it only be in the areas to do with ABS that are normally closed except when ABS kicks in? Surely air in those areas shouldn't cause a soft pedal when the entire reason you can't bleed it normally is because those areas are normally locked out by valving? But then you said you did a VCDS bleed and it did fix it, so there must be something I'm missing.

I didn't know you could do it with other OBD scan tools. I thought it was only the full VCDS or a registered VCDS lite that you could do it with? I'll have to look into that. We have one of those topdon things but I think it needs extra software for manufacturer specific procedures like that, as I thought other OBD scan apps would. We probably should do a VCDS bleed, but we weren't convinced that was the problem, as the pedal doesn't pump up and wanted to avoid the expense if it was going to be a wild goose chase.

Thanks for the input both, though it's still hard to figure out. I suppose it would help if I had previous experience of knowing what each problem feels like.

Elliott

Did you manually bleed them or pressure bleed ? Had a problem with air in my sons mk1 rear brake lines. Had changed rear brake cylinders and brakes were slightly soft after bleeding. Tried manual bleeding again but ended up using pressure bleeder and eventually got a bubble of air out. Reckon it was stuck somewhere and needed a good flow of fluid to budge it.

Alasdair

1 hour ago, Alasdair1 said:

Did you manually bleed them or pressure bleed ? Had a problem with air in my sons mk1 rear brake lines. Had changed rear brake cylinders and brakes were slightly soft after bleeding. Tried manual bleeding again but ended up using pressure bleeder and eventually got a bubble of air out. Reckon it was stuck somewhere and needed a good flow of fluid to budge it.

Alasdair

We did a normal manual bleed with me on the brakes and my dad on the bleed valves. We did this a few times and didn't use a block to limit the pedal travel, which is why we thought we'd damaged the seals. We do have a pressure bleed kit, but couldn't be bothered to find it at the time. I thought that was safer after hearing about the seal problems but I didn't know it was actually more effective.

Think there safe enough to use as long as you keep pressure down. I usually use old spare tyre at 10-12psi and have never had any problems and have done quite a few cars brakes including clutches. Generally working by myself so handy for one man bleeding. Reckon on my sons the air bubble was moving back and forward somewhere. Worth a try especially the rear

Alasdair

If you fancied a trip down the M11 with a few litres of brake fluid then I'd do the ABS bleed with you. I live in Ilford, NE London. Your choice if you want to pop by.
All that would cost you is the brake fluid and the petrol.