[Closed] Brake pedal sinks away slowly

You can check the fluid in the master cylinder. Mark where it is now and check after a day or two of use. Other option is blown seals in the master cylinder or faulty servo assistance.

as above - the way to see if you're losing fluid is not to inspect the entire braking system it's to look at that level in the master cylinder - you can do that in the rain 🙂

If you've not had a 'low fluid level' light then it's unlikely to be a leak - the light will come on way before you feel the loss of fluid at the pedal.

a slowly sinking pedal is much more likely to be air in the system or contaminated fluid than a leak - both may give an initial firm pedal but compress more than standard brake fluid over time.

Other things, duff seals in master cylinder allowing fluid past, duff brake booster seals.

how long have you had it ? has it always done it ? is it with engine off or on.

does it sink when the engine is off? assuming its a diesel then so long as the pedal doesn't sink to the floor its ok. Does it stop you properly

slowly sinking pedal will be either a servo fault of more likely IMO master cylinder seals. air in the system gives a spongy pedal and a low pedal - but once the pads are in contact then the pedal height stays the same.

https://www.pellonautocentre.com/brake-pedal-creep/

read up on diesel brake pedal creep before you go playing parts darts with any of the above guesses.

Failed seals will be failed even if engines not running. If pedal goes hard with engine off its not your seals ..... ive had this both ways - my iveco sinks once vac exhausted but was hard with engine on. . my land rover was just sinking to the floor even with engine off. - new seals in the MC solved that.

slowly sinking brake pedal could be a problem with the seals in the master cylinder,if it is this then the fluid wont be leaking out from anywhere, but it will be getting past the seals on the piston in the master cylinder and back into the main reservoir.

It might be possible to just replace the seals,or it might be time to replace the master cylinder entirely.

or it could just be the brake pedal creep referred to above

Jeez those people in Halifax talk nonsense. The fluid isn't compressible so it has to go some where. Master cylinder pressure seals leaking is the likely reason. A fluid leak a possibility that you'd notice because of dropping fluid in the reservoir (you might not see any leaking fluid as it could be leaking into the brake servo) and air in the system a small possibility (you could pump the pedal back up some of the way in this case), a balooning hose is an even remoter possibility (inspect the hoses with someone standing on the brakes, engine running)

Edit: the main nonsense from the Halifax people is "seal flipping". When you stand on the brakes at speed you can put a couple of hundred kilos on a brake pedal which translates to a ton or more on the master cyclinder plunger. The seals don't flip, if they did the unit would not be fit for purpose. So the idea you can put enough pressure into the system to flip the seal pressing back a much bigger slave cyclinder during pad cahanging when there's a hole to let the fluid back into the reservoir is nonsense.

"Jeez those people in Halifax talk nonsense. The fluid isn’t compressible so it has to go some where. Master cylinder pressure seals leaking is the likely reason. A fluid leak a possibility that you’d notice because of dropping fluid in the reservoir (you might not see any leaking fluid as it could be leaking into the brake servo) and air in the system a small possibility (you could pump the pedal back up some of the way in this case), a balooning hose is an even remoter possibility (inspect the hoses with someone standing on the brakes, engine running)"

you clearly haven't read it have you but then we all know you know everything ever without reading anything.

There is a reason the MOT testers manual says that on power assisted brakes you do the system test with the engine off.

if we are just throwing random faults at it instead of applying some diagnosis

ill throw in corroded ABS valves and also load sensing valve probably siezed.

by the time you change everything listed on here i bet youll still have the same issue as turn of the century german cars were notorious for it - and the bigger and heavier the vehicle the worse it got.

Trail Rat. I have read it, it's nonsense.

I had this on an old mini. It resulted in the master brake cylinder failing completely on the M6 in the Christmas migration stop-start traffic. I managed to get it into the services near Wolverhampton before telling my wife why we'd stopped. Fortunately the handbrake still worked! It was an expensive Christmas.
Basically, don't drive the vehicle.

Well are you going to apologise, Trail rat? Or are you going to continue bigging up the Halifax people who have fobbed off a customer without changing the master cyclinder.

Oh and I'll rubbish your suggestion:

ill throw in corroded ABS valves and also load sensing valve probably siezed.

Because those faults are not capable of absorbing several cubic cms of fluid pushed by the master cylinder and returning it to the system when the pedal is released.

You never fail to amuse edukator I've missed your comedy ego.

No comedy just trying to help the OP and give advice which is not dangerous.

It's ok. By the time he's spent all his money and has the same issue as it's a known thing on vehicles of that age he can thank you 😉

Of course that is depending if he ever actually answers the initial questions rather than just deciding it'll be fine.

Isn't the stock advice in this case to buy a Zoe ?

On a 2000 Vito on which it's the first time it's happened. What are the odds of it being and inherent design feature and what are the odds of a master cyclinder with worn seals?

Telling him to ignore the problem because "lots of big heavy German car do it" is dangerosu advice. No smiley, this is the safety of the OP and road users around him we're talking about.

Isn’t the stock advice in this case to buy a Zoe ?

Trolling on threads on critical car safety sytems. Class. But really, Trail Rat, when you haven't got a clue, don't post.

please point out where he said it just started happening.

or at least post the private email he has sent you.

hes had the car less than a week.,

He hasnt given enough information to make an accurate diagnosis.

hence why i(and oddly only I) asked further questions before playing parts darts.

at no point did i advise he ignores the issue - i am simply highlighting the FACT that there is a known quirk with vehicles of that age.

But dont let that stop you being right - it never has in the past.

I'm seeing this on two fairly modern (2010) Land Rovers.

The brakes feel solid, very solid, there are no leaks and they stop very well but if I continue to keep a very firm pressure on the pedal, it will sink very slowly to the floor. At no time do the brakes very spongy or soft.

The vehicles have been tested by Land Rover who, along with quite a few other people who know their stuff, say "they all do that".

That's great but nobody has been able to tell me why they "all do that" and with my limited knowledge of brakes I can't see why they should do apart from a fault in the MC. I can't think of anything else that could cause this fault.

yep so don't seem to be losing fluid from the system overall. reservoir full anyway and been driving a couple of days (picked it up on sunday).

it only does it when engine running, not when off. and the brakes do work, tho perhaps not as sharp as i would've expected.

from what people have said, not losing fluid implies master cylinder seals, but not doing it whe engine stopped suggests not.

so if not, would it be the servo seals? when wwaswas says brake booster, is that the same as the servo.

jesus that brake pedal creep article was painful to read! didn't make any sense and didn't really conclude with anything useful.

trail rat, 'hence why', really?

reckon i'll have a go at replacing the MC seals.

the thing is, even if 'they all do that', they presumably didn't do it when they were new, so it should be possible to get the system back to working properly.
ok, this may entail a fair amount of parts darts, as it often seems to with modern vehicles, but at least these parts aren't too pricey. a complete new master cyclinder is only 30 or 40 euros for example

another question: how do i work out if it has abs or not (apart from trying to skid!)?

and another: i guess if i buy a seals kit (€8) i just need to check part numbers for compatibilty?

yes, booster = servo.

Rather than just replacing parts (and bleeding systems with ABS can be a pain if it has it) I'd try and at least get an official diagnosis from someone familiar with the model.

Had this same issue twice.
First time was an older Defender - faulty MC seals, BUT you see this issue as black sediment in the master cylinder reservoir as the seal degrades.

Second time was my MK7 Transit. Same issue- sinking brake pedal, will pretty much go to the floor if held on brake pedal. Googled it when I first got the van (6 years ago), known 'feature/they all do it's.
Brakes fine, passes MOT's without issue, haven't crashed into the back of anyone.
I expect your Vito is the same as my Tranny

Check the MC for black sediment, find a quiet road and do an emergency stop - if the ABS kicks in/wheels lock then happy days and spend your time sorting the inevitable rust issues instead!

the main nonsense from the Halifax people is “seal flipping”. When you stand on the brakes at speed you can put a couple of hundred kilos on a brake pedal which translates to a ton or more on the master cyclinder plunger. The seals don’t flip, if they did the unit would not be fit for purpose. So the idea you can put enough pressure into the system to flip the seal pressing back a much bigger slave cyclinder during pad cahanging when there’s a hole to let the fluid back into the reservoir is nonsense.

It's nothing to do with the high pressures under breaking, most seals are designed to resist pressure in one direction. So the seals in the master cylinder are designed to resist pressure when the piston is traveling in one direction dragging it with it. Apply pressure to the slave cylinder and you apply pressure in the opposite direction of travel.

Never managed to eff up mine like that, but have always been told to open the bleed nipple before pressing the pads back in to prevent it.

Doesn't sound anything like what's happening in this case though.

Diesel pedal creep is a thing, it's the result of the smaller vacuum pump relative to the flowrate you see in petrol engines manifolds.

before i started playing parts darts i would (as i did when diagnosing my own vehicle) check the vacumn supplied by the pump is to specification and that the servo is holding .... somewhere in the region of 20-30HG

and check that the vacumn system is holding a pressure once the pump (ie engine) is off..

check the Check valve is in good nick

The issue is - mostly they did do it from new but most folk dont notice

IIRC spooky off here has a new transit that does it.

There's a difference between the long travel (but never to the floor) that's big servo related (I've owned and driven a variety of vans), and the sinking away feeling you get in the initial stages of master cylinder failure. The big servo feeling is mushy/springy with engine on.

With the failing master cyclinder it slowly sinks but doesn't spring back when you release the presure on the pedal a little. When you release the pedal and try again the bite point is normal then it sinks away again. If the master cyclinder bore is scored it may just sink to where the scoring ends (even with new seals).

ok thanks everyone. feels like we're getting somewhere, dispite the disagreements.

i should've said, and forgot to, that in the reservoir the fluid looks fairly black and murky.
i guess this could be indicative as it is if it's black in the MC?

trail rat, not sure i'm equiped to check the vacuum pump/system pressures. how do you go about it? also, is the Vacuum pump the servo?

There's only a "vacuum pump" on vehicles with no/insufficient inlet manifold vacuum to use. They use a vaccum pump instead (on the Zoé it's the wirring noise you hear on opening the door to get in - that's humour just for you TrailRat 😉 ). If you can stop the vehicle without pressing so hard on the pedal you risk breaking the seat back the servo is working.

The Halifax nosense got me wondering if there is any good advice on the net (there usually is somewhere). This covers your latest question about servos:

https://www.quora.com/Can-the-brake-booster-cause-the-brake-pedal-to-go-to-the-floor-Also-when-the-engine-is-turned-on-a-hissing-noise-comes-from-the-booster-especially-when-the-brake-pedal-is-depressed-and-the-engine-idles-rough

Edit: the latest reply is OK some of the lower ones make no more sense than Halifax.

And another thought, Junior phoned via satelite from monglia to say he'd got excessive pedal travel on his little 205. I asked if the car was pulling one way or the other. Yes, he replied. You've only got half of your split system working then, check if you've ripped off any brake pipes, then top up the brake fluid and bleed the brakes and keep topping up the fluid - that cured it apparently.

You’ve only got half of your split system working then

surely they're split front/rear not left/right?

thanks again edukator, there usually is somewhere too right. just a matter of finding it, which seems to be my weak spot : )
i'll have a read of that. hopefully there are some actual sentances in it

Diagonal split, on a lot of cars of that era. WWWaswas

thanks again edukator, there usually is somewhere too right. just a matter of finding it, which seems to be my weak spot : )
i'll have a read of that. hopefully there are some actual sentances in it...

right, good stuff. does sound like the MC, especially from your earlier description.
it spring back right away. doesn't achly feel too bad, and brakes work for now, but i reckon i'll just replace the MC, given the possibilty that a seals kit might not fix it if it's damaged inside. and given the work needed (presumably) to get to it all.

I’m seeing this on two fairly modern (2010) Land Rovers.

No such thing as a modern Land Rover since about 1950. 🙂

There’s only a “vacuum pump” on vehicles with no/insufficient inlet manifold vacuum to use.

Exactly. Or to put it another way, anything that isn't petrol powered. The OP's van will have a vacuum pump.

I once had a problem on my 1972 VW Beetle GT where the brake pedal wouldn’t compress more than a few inches so barely any braking power. Turned out approaching a sharp bend I braked and lifted, causing the AA atlas on the shelf above the pedals to slide off and get stuck behind the pedal (they come out the floor on a Beetle). Easy fix though.

I had a similar problem on my Riley Elf it turned out to be slack in my right knee joint.

All my vehicles have done this, under heavy sustained pressure the pedal will gradually creep down but with repeated application it remains firm with no sponginess. I was told it was fine and its never been an issue during MOT.

I first noticed it after doing a brake bleed on my van and obviously when doing your own work you become suspicious of anything that seems strange, but its just something you would never normally notice. Even sitting at traffic lights you would only hold the brake lightly if not using the handbrake.

there is occasionally (twice since sunday) a grunty noise before starting, comes on like fuel lifter pumps do, but sounds wrong and too loud.
did it just nowwhen i turned to third position (before sprung start position).
when i turned off and went to 3rd pos again it didn't do it, nor consecutive times.

but this made me think i had read somewhere about a vacuum pump doing this.
where is the vacuum pump? is it not driven by main auxiliary belt?

Occasionally belt driven on modern motors as they are often dual purpose/duel fluid vac and fuel or sinilar. usually they are driven direct off the cam Nd oil lubricated on most motord

In either case the motor would be running before you heard any noises

Vauxhall is recalling some Astra Ks (link) for extended brake pedal travel under slow braking. The fix includes new parts and diesel pedal creep is a thing

[i]there is occasionally (twice since sunday) a grunty noise before starting[/i]

Is it diesel? Transit is well known for actuating its EGR valve after turning off the engine to clean itself, it makes a loud chirping sound. I'm sure I've heard it at ignition on before starting on other vans.

yes diesel. it sounds like the pump on a fake espresso coffe machine, and sounds like it's struggling as it slows down over the course of 5-10 seconds.

i haven't waited to see if it stops, perhaps i should, cos i don't like the sound, so either start it or knock it off. if i knock it off without starting it doesn't come on again when re-starting. i obviously need to start wit bonnet open so i cna jump round and see if i can locate it...

Every car I've owned lets you push the pedal gently to the floor when stationary with the engine running provided you use very gentle pressure.