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Aren't modern cars supposed to be able to recover (partly) from a fluid leak?
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Good point, it should be a split system, so I was always lead to believe that if there is a leak at one wheel cylinder and that half drains, the other should still operate?
Is it possible for the master cylinder diagphram to rupture, allowing the engine to suck the brake fluid into it's air stream via the vacuum pipe?
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Sooty it is a split system, Problem lies in the fact.Master cylinder seals leak/reverse themselves so causing fluid to be pressurised in reverse direction.Not certain what you mean MCD rupture.servo has a diaphram. dont you mean servo. if so it doubfull that will happen.As front and rears are seperate as far as master cylinder is concerned.failure of seals in master cyl/will cause this.not as common as they were.though this may be one and suspect is?
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Was mech1
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Hi Sooty,
I think you are partially on the right track here.
When your foot is off the brake pedal, there is engine vacuum on *both* sides of the servo diaphragm.
When you push the pedal, the interconnection between the two chambers is first closed off.
As you push harder, atmospheric air is admitted to the chamber nearest your pedal - this is the hiss you hear if operate the brakes with the engine off. This pressure difference is what gives the assistance. To make this a progressive process there is a deformable reaction member in the valve which gets squeezed - the deformation controls the opening of the atmospheric valve.
So, there is engine vacuum sucking away at the first master cylinder seal all the time the engine is running.
I agree with Steve, this type of master cylinder failure used to be more common - I haven't seen one for a few years now.
number_cruncher
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Any brake fluid loss is dangerous. No matter what the reason. . They dont recover and if any probs with brakes. Should get sorted by profesional.Unless you know what you are doing?. Not having a go but where did you get that from?
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Was mech1
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Actually, the manual for my car. ;-) I wasn't trying to suggest that it recovers and you can keep driving it, I meant that presumably one side of the braking system should still work to an extent.
It says in the manual (terribly paraphased, sorry!) that if "one side fails the other will still work, although greater pedal pressure and travel will be needed. Do not drive the car until it's fixed."
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>>I meant that presumably one side of the braking system should still work to an extent.
If all seals fail. there is no such thing as duel braking system.
Duel system only accounts for either front or rear seal failure. ie if seal that controls front brakes fail. you still have control of rears. but with a lot more effort from foot. And depending on whether disc or drum will control braking effort. I see what you mean though.
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Was mech1
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I ws under the impression that quite a few brake systems are dual circuit, with diagonals connected (i.e. rear left and front right in same circuit) so that a degree of stability is maintained under braking in the event of one circuit failing.
Is it the case that this only helps if components on a given circuit fail, whereas if a master cylinder goes then both circuits are out of commission, hence no brakes at all?
I had an old Nova with atrocious brakes, local mechanic seemed to think that one of the circuits was playing up as always seemed to lock front drivers side wheel really easily - it was almost as if the other front brake wasn't doing anything. Scrapped it as was a banger anyway, so never actually found problem.
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Hi Dont feed the Monkeys. HAve you fixed it yet and what was the cause of all the fluid loss. Regards Peter
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Thanks all for the reply's
Sorry not had a chance to look at the Vectra since last Sunday when I checked it for leaks etc. I have been working the grave yard shift then baby sitting all morning whilst SWMBO is out at work. Add to that the purchase of new toy (Saab 9000) arranging picking it up, tax, insurance etc, selling my old Carlton, (sleeps for wimps) the poor old Vectra has just sat outside waiting for some TLC. Got a day off Saturday (after finishing night turn Fri/Sat) so hope to replace the master cylinder and clean out the servo this weekend.
Just out of interest according to the oracle (Haynes manual) the Vectra does have a dual braking circuit operating diagonally across the car NSF with OSR and OSF with NSR but this did not help much on this occasion. The brakes do work a little but its more like rolling up an incline than brakes, no way is the car drivable like it is, hence it had a ride home on flatbed whilst I dashed off to pick up a hire car to complete my journey.
I just thanked god it happened when I was driving and not when SWMBO had planned to be driving at break neck speed in heavy traffic later in the day.
Will post findings Sat or Sun night.
Many Thanks
Steve.
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>>Vectra does have a dual braking circuit operating diagonally across the car NSF with OSR and OSF with NSR but this did not help much on this occasion.
well not to upset anyone. it wasnt a good idea. Duel system should I believe be front/rear/split brakes. Unless of course master cylinder packs up. I expect others to dissagree?
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Was mech1
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Hi Dont feed the Monkeys. HAve you fixed it yet and what was the cause of all the fluid loss. Regards Peter<<
Job done.
Took off the master cylinder and found the servo full (and I mean full) with brake fluid. Syphoned most of the brake fluid out, spent ages cleaning / drying out the servo, bolted new master cylinder on, bleed the brakes and Bobs me uncle a car that stops better then it goes. Job was actually a lot easier than I had expected.
Monitoring brake fluid level very closly for the next few weeks just to make sure.
Many thanks for all the help and comments, I thought the master cylinder was at fault but to have confirmation from those with better knowledge was a great comfort.
Steve
DFTD
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>>I ws under the impression that quite a few brake systems are dual circuit,
I dont think there are any that arent. though could be wrong?
>>Is it the case that this only helps if components on a given circuit fail, whereas if a master cylinder goes then both circuits are out of commission, hence no brakes at all?
Thats about right.
I had an old Nova with atrocious brakes
IIRC Vx tried cross duel braking on the HC Viva and as I recall
it was a failure. I do know there were many a mechanic that said it was a bad Idea. But that was during my Apprentice days so may it may never have been introduced
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Was mech1
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It has been a while since I stripped down a dual circuit master cylinder, such is their reliability, but I seem to remember that the master cylinder effectively has 2 sets of pistons & pressure outlets (easier to draw than explain)in 1 bore.Failure of a brake pipe,cylinder etc OR failure of seals on either piston means that you still have one set of brakes but the pedal goes down further.
Of course you can still have complete failure if one component from either system fails simultaneously.
What happens often is that a failure is gradual, and the driver gets used to reduced braking and increased pedal movement, or simply ignores it, and then you have a second failure (not suggesting it happened in this case though)
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Some cars have a sensor that detects any difference in pressure in the two circuits and causes a warning light to come on. This warns of the kind of gradual failure Dave mentions.
I think the expression "dual circuit" is misleading and potentially dangerous. It gives the impression that in all circumstances one half of the braking system will still function. A true dual circuit system would have twin master cylinders, totally unconnected and fed from separate reservoirs.
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