Manufacturers would make us believe that fluid needs to be changed every 2 or 3 years. Any opinions on the small electronic testers available on a well known auction site for around £20 to check by oneself if it needs to be changed?
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No opinion on the tester, but for piece of mind I'd rather it just be changed at the recommended interval and be done with it.
My dealer charges something like £30 for a brake fluid change. Small price to pay every 2 years.
Yes, I know once the tester has been bought, it will eventually pay for itself. Providing of course that it is accurate.
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Bell Boy posted this some time ago: workshop.search-autoparts.com/_Can-You-Believe-This/video/486759/31710.html
My own results seem to indicate it's kosher.
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You beat me to it bathtub.
I change my brake fluid every 2 or 3 years if I keep the car that long, or include a fluid change when carrying out any other work involving dismantling the brakes. It's not a costly job.
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The electronic tester only tests the fluid in the reservoir. The fluid in the brake cylinders (which are probably the most important locations) could conceivably have a different boiling point from the fluid in the reservoir. Here's some information about brake fluid. tinyurl.com/y94o2w3
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Natural curiosity leads me to question some of the “change brake fluid” assumptions.
Where does the water come from? The master cylinder has a small vent in it to allow the level to drop as the pads wear. This is a vent hole, not an air circulation hole and the amount of water entering this way must be miniscule. If the water is creeping in at the wheel end of the system then the brake pedal must feel “spongy” very quickly. If water is being drawn in then so must air, in much greater quantities (by volume) to carry the water.
Are the boiling points in L’escarcot’s link at atmospheric pressure or a “typical” brake application pressure?
If the braking system holds, say, 1 litre of fluid, then to get 3% water content a rough calculation gives an air ingress of something like 4 cubic meters. How does that amount of air affect the brakes in a 1-litre system?
If the water is coming through the hoses then air should be as well.
The Xantia uses a non-hygroscopic mineral fluid so I don’t have the problem.
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>>The master cylinder has a small vent in it to allow the level to drop as the pads wear.
Under bonnet temperature changes mean the contents expand and then contract on every journey. Enough to push out a small amount of air and pull some back in. Even when the car's not used, the difference between day and night temperatures has the same (albeit somewhat lesser) effect.
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The lancer has a bellows type membrane under the master cylinder cap, allows the level within the reservoir to change without exposure to the outside air.
I have no fear of the boiling point being reached, modern ventilated disks dissipate more than enough heat away to prevent this point being reached under normal or even abnormal driving conditions.
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The problem area for water content is obviously near the wheel cyclinders/calipers as these are the parts that heat up when braking and where the moisture if any will boil.
Sounds simple? Yes. It's obvious.
And people test the fluid in the master cylinder.. which by definition does NOT circulate round the system..
Sounds wrong? Yes: testing the master cylinder fluid is imo a waste of time.
I change mine every three years.. The additional benefit is that all bleed valves are de-rusted and when tightened protected with a coat of waxoil/dinitrol.
Ever tried moving a bleed valve untouched for 6 years? If unlucky, it is rusted solid and snaps.
I speak as one who keeps cars for at least 5 years and possibly a decade or more..
Last edited by: madf on Thu 19 Jan 12 at 15:49
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Thanks for the comments. I had not considered rusting and I think that is more relevant than the water content.
Thank you.
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I don't think modern DIYers realise what filthy muck can be inside their braking hydraulics.
Rust also isn't just a problem outside the system either, i've stripped and rebuilt slave cyls and calipers and master cyls when funds were tight, seeing the rust on the inside of steel slave cyls where the brown sludge that was once clean fluid is an eye opener.
People of the parts throwaway not rebuild era maybe have never seen this.
Interesting link above from Tom, i once had to work on a Renault 11 (i think) that had been neglected like that car, the front discs were literally wafer thin, how one earth they didn't break up in use is a mystery, had a 2CV one day that didn't stop very well either, found one pad had disappeared completely and it was braking on the piston which had formed a baseball cap shape and was about to exit the caliper as it wore down.
I wonder if the owners ever talk about car refinement, foriegn to them as they couldn't feel the dangerous symptoms beneath their braking foot.
Should have kept and camera and a rogues gallery, being a kerbside cowboy who took a pride revealed some gems.
Last edited by: gordonbennet on Sat 21 Jan 12 at 15:01
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Ford Fiesta - 09 1.2 Brake fluid and water content - VxFan
