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Had this happen to me several years ago. Braked coming to the end of the street going to work and pedal went strait to floor, pumping it made the brakes work. Carefully drove 200 yards home and brakes seemed to work fine. Fluid reservoir full. Caught bus.
Bled brakes later that day but it happened again a week or so later.
Spoke to fleet mechanic at work and he said master cylinder seals so I bought a repair kit. Took one look at it and returned it for a replacement master cylinder, only a few pounds more. Swapped master cylinder, bled brakes and it never happened again in the 3 or so years I had the car.
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The trouble with these "I replaced the master cylinder and the problem was solved, so it was a faulty master cylinder" anecdotes, of which there are many, is that the brake system was probably bled, flushed and fluid replaced when the master cylinder was, so you don''t actually know what fixed it.
I had a total brake failure on the Skywing about 6 years ago. Everybody and his dog on the Internyet had it as master cylinder failure and was calling me names for not replacing it (I replaced the brake fluid a leaking wheel cylinder, and the brake shoes) but 6 years later its still working.
I THINK it was boiling brake fluid, compounded by a detached brake shoe lining which was cooking up a back brake.
It COULD have been the master cylinder though, and so could this.
Since extensive work has apparently already been done, the brake fluid in this case has probably already been replaced without fixing the problem
Edited by edlithgow on 30/10/2019 at 02:39
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The trouble with these "I replaced the master cylinder and the problem was solved, so it was a faulty master cylinder" anecdotes, of which there are many, is that the brake system was probably bled, flushed and fluid replaced when the master cylinder was, so you don''t actually know what fixed it.
I had a total brake failure on the Skywing about 6 years ago. Everybody and his dog on the Internyet had it as master cylinder failure and was calling me names for not replacing it (I replaced the brake fluid a leaking wheel cylinder, and the brake shoes) but 6 years later its still working.
I THINK it was boiling brake fluid, compounded by a detached brake shoe lining which was cooking up a back brake.
It COULD have been the master cylinder though, and so could this.
Since extensive work has apparently already been done, the brake fluid in this case has probably already been replaced without fixing the problem
Is that the long way of saying you agree with the diagnostics over the intrnyet. ;)
master cylinder seals used to be a common failure, probably due to material makeup or just the makeup of the fluid.
though they often scored the cylinder bore if left too long so replacing just the seals was a waste of time
Edited by bolt on 30/10/2019 at 07:57
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The trouble with these "I replaced the master cylinder and the problem was solved, so it was a faulty master cylinder" anecdotes, of which there are many, is that the brake system was probably bled, flushed and fluid replaced when the master cylinder was, so you don''t actually know what fixed it.
Not on mine, read my post, here is part of what I said
Bled brakes later that day but it happened again a week or so later.
Suppose you will now say I did not bleed them correctly the first time.
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The trouble with these "I replaced the master cylinder and the problem was solved, so it was a faulty master cylinder" anecdotes, of which there are many, is that the brake system was probably bled, flushed and fluid replaced when the master cylinder was, so you don''t actually know what fixed it.
Not on mine, read my post, here is part of what I said
Bled brakes later that day but it happened again a week or so later.
Suppose you will now say I did not bleed them correctly the first time.
Here's.....Wickipedia
Brake bleeding is the procedure performed on hydraulic brake systems whereby the brake lines (the pipes and hoses containing the brake fluid) are purged of any air bubbles."
So IF that's what you mean by "bled brakes" (lot's of ways to do it, much argy-bargy on the nyet. many Americans predictably don't think it can be done without a fairly expensive gadget) then your objective was purging air bubbles, (which you probably didn't have) NOT changing your brake fluid.
I dunno how much fresh fluid you introduced, or whether it would be enough to address a contaminated system, nor do I much care, since I wasn't commenting on your failure specifically. (Read MY post)
I was commenting on mine, and (by extension) noting a general knee-jerk tendency to replace master cylinders without eliminating the alternatives.
This doesn't seem to apply in this case, as I've said.
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Brake bleeding is the procedure performed on hydraulic brake systems whereby the brake lines (the pipes and hoses containing the brake fluid) are purged of any air bubbles."
Know that, been on the road for about 45 years now so plenty of experience.
So IF that's what you mean by "bled brakes" (lot's of ways to do it, much argy-bargy on the nyet. many Americans predictably don't think it can be done without a fairly expensive gadget) then your objective was purging air bubbles, (which you probably didn't have) NOT changing your brake fluid.
Most times bleeding has been carried out to change the fluid, very rarely had problems with a soft pedal because of the maintenance I carry out.
Back in the 70's bleeding was always a 2 person job, one pumping the pedal and one operating the bleed nipple and checking the reservoir.
Then I bought one of those bleed pipes with a non return valve in that supposedly made it a one man job, useless, always got more air in the system after the bleed then there was before, mechanic at work said it was because air could enter around the nipple threads.
Late 80's bought a Gunsons device that use pressure from the spare tyre to force brake fluid through the system. One man job, works brilliantly, still using it now.
I dunno how much fresh fluid you introduced, or whether it would be enough to address a contaminated system, nor do I much care, since I wasn't commenting on your failure specifically.
Always put enough through to ensure its a complete change and a bit more.
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Then I bought one of those bleed pipes with a non return valve in that supposedly made it a one man job, useless, always got more air in the system after the bleed then there was before, mechanic at work said it was because air could enter around the nipple threads.
in some the non return valve was a split in the closed end of pipe that opened to allow the fluid through, but often the split did not seal when the pressure was released and sucked air back in just as the bleed nipple thread did.
I went back to 2 man job after trying one out, it was quicker and you knew all the air was extracted from the system
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I use an enema syringe for brake flushing / bleeding.
Cheap and effective, giving complete control and allowing you to suck, blow, or cycle, and apply quite a lot of pressure if you aren't scared of everting master cylinder seals.
However much pressure I applied it didn't get sludge out of my contaminated calipers. That required a full strip.
Never used it with ABS though, since I've never had ABS, (and don't much want it.)
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if you aren't scared of everting master cylinder seals.
If they are in good condition you would find it hard to evert seals from one of those, be interesting watching someone try ;-)
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if you aren't scared of everting master cylinder seals.
If they are in good condition you would find it hard to evert seals from one of those, be interesting watching someone try ;-)
Considering that brake pressures are in the region of 30 to 70 bar I would doubt that an enema syringe could do any damage. Just imagine what would happen to the recipient if 70 bar was stuffed up their nether regions.
The Gunsons device I use suggests 30 psi (2 bar) which works just fine. I doubt that an enema syringe could manage that.
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if you aren't scared of everting master cylinder seals.
If they are in good condition you would find it hard to evert seals from one of those, be interesting watching someone try ;-)
Considering that brake pressures are in the region of 30 to 70 bar I would doubt that an enema syringe could do any damage. Just imagine what would happen to the recipient if 70 bar was stuffed up their nether regions.
The Gunsons device I use suggests 30 psi (2 bar) which works just fine. I doubt that an enema syringe could manage that.
Dunno. Can't remember if I've measured it, but I've seen this raised as a concern in discussions of the upward flush/bleed technique. Didn't bother me, and Iin the past I've applied as much pressure to it as I was physically able, but it does bother some people.
IF, for example, the pressure is being applied on the wrong side of a seal (I'd have to look at some diagrams to remind myself if that's likely, but a priori it seems at least possible) then a relatively low pressure might be a problem. .
Logically an enema (or any) syringe can manage as much pressure as you can apply to it, until it bursts, and they are pretty strong.
I use a bicycle pump (basically a less well made syringe) to top up tyres, and this can easily manage in excess of 30 psi, so I'd expect a syringe to go quite a lot higher.
When I've been trying hard there was significant visible upwelling into the MC reservoir, though I don't do that any more.
Edited by edlithgow on 31/10/2019 at 12:10
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Then I bought one of those bleed pipes with a non return valve in that supposedly made it a one man job, useless, always got more air in the system after the bleed then there was before, mechanic at work said it was because air could enter around the nipple threads.
in some the non return valve was a split in the closed end of pipe that opened to allow the fluid through, but often the split did not seal when the pressure was released and sucked air back in just as the bleed nipple thread did.
I went back to 2 man job after trying one out, it was quicker and you knew all the air was extracted from the system
Fit some Stahlbus bleed nipples, they are a two part bleed valve with a spring loaded ball valve inside, all o-ring sealed, they don't leak air in when bleeding, turns bleeding ito a one man job, pump pedal, top up reservoir, job done.
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I put PTFE thread tape on the bleed nipple threads which reduces the chance of them sucking air, though that isn't mostly why I do it.
I'm mostly doing it for anti-seize effect, to stop the nipple corroding solid.
Air entrainment isn't really a problem using a syringe. Turns bleeding into a one man job, DONT pump pedal, top up reservoir, job done.
When sucking, with an upward orientation of the bleed tube, any bubbles entrained rise into the syringe, where they are harmless.
When blowing, you've got positive pressure so air entrainment doesn't happen. There might be some weepage (if thats a word, or even if it isn't) of brake fluid past the threads, which doesn't matter.
But if you like shiny new nipples, why not?
It's only money.
Edited by edlithgow on 01/11/2019 at 04:21
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Sounds exactly like a problem I had on my S-Max, car repaired (new design Non return valve) by dealer after I nearly crashed into the neighbours house, the dealer new exactly what it was. Not sure if relevant as your brake design may be different. There was a recall later, the problem was a sticking non return valve in the vacuum pump where before the valve frees itself you lose boost and brake efficiency.
It was Ford recall R/2009/050 if you want to investigate.
Edited by Ian D on 01/11/2019 at 07:25
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Sounds exactly like a problem I had on my S-Max, car repaired (new design Non return valve) by dealer after I nearly crashed into the neighbours house, the dealer new exactly what it was. Not sure if relevant as your brake design may be different. There was a recall later, the problem was a sticking non return valve in the vacuum pump where before the valve frees itself you lose boost and brake efficiency. It was Ford recall R/2009/050 if you want to investigate.
Seems like good info. but also an illustration that ALL intermittent brake faults aren't necessarily due to the master cylinder, so I'm afraid it won't be a very popular explanation.
However, my understanding is that brake vacuum pumps are a characteristic of diesel engined vehicles, which, due to a lack of throttle body restriction, don't generate a reliably usable level of intake manifold vacuum.(My Renault-Dodge Truck had one)
IF this is the case (Could be out of date. No experience with new cars and don't much want any.) and IF Hyundai Coupe's don't have diesel engines (coupe and diesel didn't use to be commonly associated words) this particular explanation seems unlikely to apply to this case.
Edited by edlithgow on 04/11/2019 at 02:02
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but also an illustration that ALL intermittent brake faults aren't necessarily due to the master cylinder, so I'm afraid it won't be a very popular explanation.
Whats popular explanation got to do with it, the symptoms given by the OP are the same as has occurred on master cylinders in the past.
and has also been questioned by some because they do not think a M/C will cause problems, but until its proved either way we dont know, its not often it occurs these days but occasionally you do get one
But nothing to say its not something else
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