car bodging

[Adrian]

Of course, an even easier option would be to use a non-hygroscopic fluid...

But, no. It seems that's not an option. The one manufacturer who did have gone back to DOT.

[Tim Watts]

That's basically it.

[polygonum]

WHAT boils at a lower temperature? The water in the brake fluid + water mixture? Or the brake fluid itself?

I still cannot see why the boiling point of the brake fluid should reduce. Please, please explain it to me.

I am genuinely happy that people are changing their brake fluid. I do agree it is a good thing to do.

[polygonum]

Who was that? And what did they use - silicone?

[Tim Watts]

Because it absorbs water over time from the air (via the breather hole in the cap for one).

[Tim Watts]

It matters not - if some fraction of the mix boils, the brakes fade. It doesn't matter if the hydraulic fluid is OK, whilst the water is boiling off.

[polygonum]

It matters in that they are two different mechanisms. Either might be quite able to let you crash your car because it won't stop.

[Clive George]

Over in bike-land, disks seem to be a mix of DOT and oil. Shimano and Magura do oil (though Shimano claim theirs is super-special), Hope and Hayes DOT. Much as I would love to support my local bike part maker (Hope factory 20 miles from here), I wouldn't necessarily get another one of their disks, purely because of the fluid. I think I've been spoiled by the green stuff :-)

[Clive George]

No, it doesn't matter. The important thing is the boiling temperature of the mix. The presence of the water renders the hydraulic fluid "not ok".

If you remove the water, yes, the boiling point of the brake fluid will go back up. But that's hard.

Presumably the concept of a mixture changing the boiling point isn't that odd to you? Adding salt to water raises the boiling point, adding alcohol lowers it. Same general concept.

has a nice graph.

FWIW the non-hygroscopic brake fluid Adrian mentioned is Citroen LHM. It's less finicky than DOT, though the mechanism for using it is different too - the force for the brakes comes from a pump + gas pressurised reservior (accumulator sphere), not your foot. The pedal just opens a valve. I've not had anything else for quite a few years now :-)

[Huge]

No it doesn't.

[tabbypurr]

Light surface pitting doesn't cause failure, the pipe's thick. But it will at some point.

FWIW there was also an arrangement where vehicles had dual circuit brakes yet failure of one circuit caused 100% failure on all wheels. My Y reg car had that. If you drive an old car you might have that setup. (Y at the end not the beginning.)

First thing to do is pump the pedal. It often works.

Funny how things change. I've driven things no-one would put on the road nowadays.

NT

[tabbypurr]

Speaking of boiling, look up Cuban brake fluid. Water, alcohol, sugar! And a dash of shampoo.

NT

[Adrian]

It doesn't always... There are normal master cylinder braking systems that use LHM...

[Harry Bloomfield]

Clive George a écrit :

No, it is not that difficult...

A manufacturer would simply need to seal the reservoir breather with a flexible diaphram. Most of the moisture ingress to the fluid enters the fluid via the breather in the reservoir cap.

My clutch hydraulics are described as 'sealed for life', supposedly no need to change the fluid unless a part fails. Motocycles also use a diaphram seal in the clutch and brake reservoirs.

[The Natural Philosopher]

Your first idea is the right one. The water in the fluid turns to steam, and that means a huge increase in elasticity in the fluid, and soft or non existent brakes.

The simple way to say that is 'boiling brake fluid'

It is a good idea. I'd say 5-20 years rather than 2 though.

But 2 is good from the POV of corrosion. Ive replaced cylinders and so on back in the day and indeed more recently and corrosion is what causes your cylinders to fail. Whether brake fluid change every 2 years is cheaper than a calliper after 10 is a moot point though.

[Harry Bloomfield]

[e-mail] a écrit :

Back in the bad old days, I had a company car's single circuit brakes fail on a hill down slope, on a back road, in Wales. Remember they only fail when you use and need them. Not fun decending a hill with no brakes. I put the handbrake on, used the lowest gear, but neither enough to slow down, so I had to run it along a soft hedge to slow it down.

I now habitually apply maximum pressure on the pedal, with the engine running and whilst stood. That pressure will be far higher than you would achieve in normal braking and is a better, more conclusive test than looking at the pipes. No one can inspect the entire length of the pipes for defects.

Clean them up, oil them, leave it to soak in, then grease them. If you can then add some of that small, split electrical tube (commonly used on car wiring), at the more exposed sections - all the better.

[The Natural Philosopher]

On 18/05/16 21:03, polygonum wrote: But none of them

If you have a true mixture of water & hydraulic fluid, and it boils (the solution) is that brake fluid boiling, the water boiling or the mixture boiling?

I think you are just as lacking in understanding as the person who said casually 'the brake fluid boils'.

The fluid in the brakes does indeed boil.

[Capitol]

They don't need to if you hit a pedestrian or a child. I agree with Andrew, replace them with copper.

[cl]

That's my understanding of how a genuine solution 'boils'. There's no separate boiling of the two constituents at different temperatures, the boiling point is some new value which I guess is usually between the boiling temperatures of the two constituents.

E.g. add salt to water, it dissolves and the boiling point of the resultant solution is higher than that of pure water.

So I would guess with brake fluid when you add water the boiling point reduces somewhat but what *doesn't* happen is that the water in the solution boils at 100 degress Celsius.

[Capitol]

Corroded pipes, stored in a damp environment will decay at quite a fast rate. I've just had a case where the drum brakes seized due to rust, where the car is stored in a heated garage. There is enough moisture around to do damage.