Brakes: Brake fluid - test or replace?

[morsing]

Hi,

Do you replace brake fluid routinely, or rely on a tester to tell you?

It's been a couple of years, but my tester shows up green, so leave or replace?

Thanks

[volvo again]

Your tester will only test the fluid that's in the master cylinder, what about fluid in the calipers and lines?
My opinion...change it all

[Othen]

Originally Posted by morsing

Hi,

Do you replace brake fluid routinely, or rely on a tester to tell you?

It's been a couple of years, but my tester shows up green, so leave or replace?

Thanks

Brake fluid doesn’t wear out, it just absorbs water if exposed. The only place it is exposed is at the master cylinder, so if you test it and it is okay then there is no need whatsoever to change it.

The business of changing brake fluid every 2 years or so is just made up by garages to invent business. I test it myself in all my cars (including my Porsche) and only change it if the tester indicates a need.

Alan

[morsing]

Originally Posted by Othen

The only place it is exposed is at the master cylinder, so if you test it and it is okay then there is no need whatsoever to change it.

Alan

Yeah, that was kinda was I was thinking...

Thanks

[Familyman 90]

Replace it. As most excellently pointed put above, testers only work on the fluid in the reservoir.

Brake fluid is hygroscopic. Most contamination will come via the master cylinder cap, but sufficent molecular exchange takes place via the flexible lines themselves - hence fluid becoming visibly mucky with age - and the circulation of fluid around the system is so slow that it is not appropriate to rely on a tester that probably cost more than a bottle of decent fluid anyway.

If one can't afford/can't be bothered to attend to something so critical they shouldn't be on the road. Do it exactly at the time/mileage interval Volvo recommend and throw the tester in the bin.

[Othen]

Originally Posted by morsing

Yeah, that was kinda was I was thinking...

Thanks

Opinions vary on this, just like almost every aspect of maintenance. The Porsche specialist I use, whom I trust, agrees with me that regular (annual) testing is perfectly adequate. I do the same on my other cars and bikes.

I have no view on what other people should spend their money on, but I certainly won’t encourage them to waste it unnecessarily.

:-) Alan

[DaveNP]

I neither routinely test or replace brake fluid, but then if I do anything to the brakes, even just replacing the pads, I'll get a bottle of fluid and bleed the system until the new fluid runs through, and then go round all four wheels again to be sure. At under a tenner a bottle it's cheap enough to do, big question is what to do with the row of half bottles in the garage that I'll never use because they may well be degraded by moisture?

[baggy798]

I change it every 3 years.

[ITSv40]

I change every two years. I never understand why folks would skimp on brakes or tyres, it just doesn't make sense. Or indeed any other safety related item.

[Othen]

Originally Posted by DaveNP

I neither routinely test or replace brake fluid, but then if I do anything to the brakes, even just replacing the pads, I'll get a bottle of fluid and bleed the system until the new fluid runs through, and then go round all four wheels again to be sure. At under a tenner a bottle it's cheap enough to do, big question is what to do with the row of half bottles in the garage that I'll never use because they may well be degraded by moisture?

As long as you fasten the half bottles with a secure top they will be fine.

Let's think about it: the water vapour content of air by mass is about 0.01% in your cold garage, air weighs about 1.5kg/m^3, and there is perhaps 500cc of air in your half used bottle, so there is 0.005*1.5*0.0001kg = 0.00000075kg of water in the air inside the bottle or 0.75mg. The remaining brake fluid weighs about 500g, so even if it absorbed all the a water vapour (and it cannot of course because of the partial pressures) then that would only be 0.00075/500=0.0000015 or 0.00015% contamination.

:-)