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We all know the dire warnings about the fragility of iABS systems if the fluid isn't regularly ( annually ? ) changed, but in the real world what's the truth ?
So, how often do you change your fluid , and how many iABS units have you had fail on you ? ( sort of unofficial survey )
Truthful answers please ... if you've got lazy or poor and have left it 7 years don't be ashamed tell us about it.
I'm getting myself psyched up to change mine for the first time and can't help wondering "why" ? What happens to the fluid in one year that is so dramatic ?

My 12s is now coming up for 9 years old, I've had it for three of those and as far as I know has never had the brake fluid changed. I plan to do it this year.

My BCR was 8 years old before the fluid was changed

Not done it since mind and it's just had its 12th birthday!

Yearly change my arse

DT

I tend to change fluid every 2 years, for two reasons:

- since it is hydroscopic it WILL absorb moisture that will in turn lead to some corrosion inside the brake system, which I imagine will a bunch of complex and expensive components on an ABS bike. It'd be interesting to understand if these units are vulnerable to this moisture.
- the absorbed water will lower the boiling point of the fluid and therefore the performance of the braking system will be compromised (assuming that at some stages in the riding year it is used heavily).

Basically I like a reliable and good performing brake system. A BFC is simple and cheap on non ABS bikes (all mine are) so why not?

jeznewsome wrote:I tend to change fluid every 2 years, for two reasons:


- the absorbed water will lower the boiling point of the fluid and therefore the performance of the braking system will be compromised (assuming that at some stages in the riding year it is used heavily).

I've never understood this "apparent" phenomenon .......

(I may regret this............)

Under the pressure imposed on the system under braking - the boiling temperature of the included water (if any) is raised sufficiently - to obviate any phase-change and associated sponginess.



What the water will do, I think - is to change phase upon release of the brake, and tend to overflow the reservoir.

Al

Blackal wrote:

jeznewsome wrote:I tend to change fluid every 2 years, for two reasons:


- the absorbed water will lower the boiling point of the fluid and therefore the performance of the braking system will be compromised (assuming that at some stages in the riding year it is used heavily).

I've never understood this "apparent" phenomenon .......

(I may regret this............)

Under the pressure imposed on the system under braking - the boiling temperature of the included water (if any) is raised sufficiently - to obviate any phase-change and associated sponginess.



What the water will do, I think - is to change phase upon release of the brake, and tend to overflow the reservoir.

Al

Seems to make sense.

What about release and immediate (heavy) re apply?

What typical pressure will occur by the way? (Not trying to be clever. I sincerely don't know!)

Not sure what pressures are likely, to be honest.

This fella wrote a paper on Motorcycle Braking Dynamics


http://www.pcbrakeinc.com/epub/aiqwinte ... brakes.pdf

But seems not to consider the phase-change under pressure, since it appears kind of outwith the main subject-matter?


9.3. BRAKE FLUID VAPORIZATION
Brake fluid vaporization occurs when the brake fluid in the front (or rear) caliper wheel
cylinder exceeds the boiling temperature of the brake fluid. Brake fluid vapor assumes a
significantly larger volume than liquid brake fluid, causing a compressible vapor pocket.
The front (or rear) brake system cannot be pressurized effectively, resulting in partial or
total front brake failure. The boiling temperature of brake fluid is a function of the type
or quality of brake fluid used, and fluid contamination by water. Since brake fluid is
hygroscopic it will absorb water naturally. Water will enter the brake system through
the flexible brake hoses. Motorcycle brake maintenance must include regular brake fluid
changes.
References:
1. Accident Investigation Quarterly, Summer 2007
2. Accident Investigation Quarterly, Fall 2007
3. Brake Design and Safety, Rudolf Limpert, 2nd Edition, SAE International, 1999.
4. Unfallrekonstruktion, Volume 2, Wolfgang Hugemann, autorenteamGbR, 2007.
Note: The latest accident reconstruction software MARC 1 is available at no cost from
the PC Brake website: www.pcbrakeinc.com under link to MA

Blackal wrote:
.......What the water will do, I think - is to change phase upon release of the brake, and tend to overflow the reservoir.

Al

I'm not taking you literally here. To actually overflow it would have to burst the rubber bellows. More likely is it to keep pressure in the system, causing brake bind even though the lever is released? Sound feasible?

Regarding operating pressures I have come up with around 250 psi for a pre- radial type, with a 5/8 cylinder. Sound ok?

If any of this is on track then it would create a kind of positive feedback system. The initial heat build up. The release of the lever, lowering the pressure to atmosheric. The boiling. The brake bind continuing to feed heat in. The reapplication of lever. The panic as nothing happens!

Oh eck.



(Not read your link at this point, so apologies if any of this is included)

You should at least check the fluid. Here's a before/after pic on my BCR:

Tapio: what make the old fluid dirty and black?

Blackal: your point on the high pressure maybe preventing boiling is a sound point in my view. But the pressure fluctuates wildly and steeply. As soon as it returns to atmospheric the heat built up will get to work. I have had exactly these symptoms in the past. At the time I was surprised how long it took the heat to have done its thing, but I didn't take into account how the high pressure might have deferred the phase change.

Bottom line. If you're heavy braking from high speed with old fluid, you run the risk of boiling. Imo.

Then there's the internal corrosion risk.

The absorbed water is a very small quantity. If the water is going to boil it will be at the callipers, thereby causing small vapour bubbles. With repeated heavy use of the brakes you will experience the brakes become spongy which will require the fluid to be changed. Interestingly brakes reaches a maximum temperature 16 sec after use, so by the time you need to apply the brakes again it has become all spongy.

The car gets a brake fluid change 1st service after winter and the bike every year after winter.

Tapio wrote:You should at least check the fluid. Here's a before/after pic on my BCR:

I have 'never' seen brake fluid look like your 'before' picture. Even though mine has probably never been changed (certainly not in the 3 years ive had it) it still looks only slightly darker than new.

Don’t know much about this (or anything else for that matter) but that’s never stopped me before.

If it’s a closed system with all voids filled with a (virtually) incompressible fluid, be it brake fluid or brake fluid and a little water, then when it starts to boil and turns to vapour, the pressure must increase a huge amount (same mass of water vapour is approx. 1700 times the volume of water) so wouldn't the pressure increase stop the boiling as per Blackal post? When brakes fade, is there something else happening…

http://ebcbrakes.com/articles/what-is-brake-fade/

or is it gas escaping into the reservoir and so losing pressure in the system or a bit of each?

I agree with changing on a regular basis, water and or air in the system can’t be good for the components as will cause corrosion.

As an aside, I stripped and cleaned the callipers on the Bandit recently. I know how they work but when you see its’ just a rubber (?) O ring that stops all the oil spraying onto the discs, it’s quite impressive really. Well, I thought so anyway.

It’s also a wonder how far the corrosion gets inside the calliper, right in the recess of the oil seal and that’s passed the dust seal, you can see where the crap comes from.

I had a GSX-R1100 that had never had the clutch fluid changed, and one day when riding it the clutch started slipping when the engine got up to temp.

It turned out to be the fluid, as changing the fluid completely fixed it. It seemed illogical, and I concluded that the clutch hydraulic system must be sealed, unlike the brake. I.e. it is not open when released, and cannot adjust for wear.

On a similar theme, old bevel drive Ducati brembo master cylinders are usually trashed by moisture in old fluid when they have been stood for a few years. They get quite substantial corrosion in the bore.

Topcat wrote:Don’t know much about this (or anything else for that matter) but that’s never stopped me before.

If it’s a closed system with all voids filled with a (virtually) incompressible fluid, be it brake fluid or brake fluid and a little water, then when it starts to boil and turns to vapour, the pressure must increase a huge amount (same mass of water vapour is approx. 1700 times the volume of water) so wouldn't the pressure increase stop the boiling as per Blackal post? When brakes fade, is there something else happening…

http://ebcbrakes.com/articles/what-is-brake-fade/

or is it gas escaping into the reservoir and so losing pressure in the system or a bit of each?

I agree with changing on a regular basis, water and or air in the system can’t be good for the components as will cause corrosion.

As an aside, I stripped and cleaned the callipers on the Bandit recently. I know how they work but when you see its’ just a rubber (?) O ring that stops all the oil spraying onto the discs, it’s quite impressive really. Well, I thought so anyway.

It’s also a wonder how far the corrosion gets inside the calliper, right in the recess of the oil seal and that’s passed the dust seal, you can see where the crap comes from.

First off, it's interesting to think whether the system is "open" or "closed". In my eyes, using the terms as commonly accepted, it's open. But not fully!

As a principle the system is designed to operate using atmospheric pressure as a starting point. It tops itself up using atmospheric pressure and is primed ready to go at atmospheric pressure. It would function, in principle just fine with no lid on the reservoir. The lid stops crap getting in, holds the bellows in place (which is also there I guess to keep the actual atmosphere from interacting), stops the fluid swishing out and gives the bellows a hard limit of expansion. This last point is what I see as the fact which really allows the system to become "closed", given certain criteria occurring. Namely, excessive expansion.

The amount of "free " volume for the system to expand into, on a released lever, is dependant on the initial fluid level in the reservoir, at normal ambient temperature and pressure.
We can't get away from the fact that water boils at a higher temperature as the pressure rises, as per blackal's graph. What you've described above is pretty much a catch 22 situation. Once the lever is released after a heavy braking incident, which we'll say has put a lot of heat into the system, the water would boil. If the amount of expansion exceeds the free volume in the res, then pressure would build up I guess. It'd have no option! What you're saying is that the re increased pressure would raise the boiling point and stop the expansion. Catch 22.

Interesting conundrum.

I don't know what happens next, but the initial boiling is best avoided in the first place!