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Hogwylde 23rd May 2009 18:28

Brake fluid
A friend and I were discussing brake fluid as my bike is 10 yrs old and he said I should change the brake fluid. I had never heard of such a thing as I had never just changed it, unless I was rebuilding the master cylinder, etc. But he said one should as it could get contaminated over time.

So of course after riding yesterday, it seemed as though my rear brake was pulsating lightly as if I had ABS and it got me to thinking about our conversation.

I've got new pads which probably have ~5,000 miles on them.

Any thoughts?

bigjnsa 23rd May 2009 18:32

I would think you should replace the brake fluid once a year.

zenfrogmaster 23rd May 2009 19:08

+1 for an annual fluid change - it's quick and easy, and good insurance. That won't address your pulsing rear rotor, which just might need a quick scrub.

Tin Man 2 23rd May 2009 19:42

I bleed my brakes once a year simply to bleed out moisture at the caliper. I might flush all the fluid once every 3 yrs or so, again what you are fighting is moisture in the system. You may have heard of racers flushing more often as extreme heat is an enemy that may cause a breakdown in the additive package, just like in motor oil. I would bet money that 90% of street bikes never get fresh fluid !!

mid30 23rd May 2009 19:46

Could be a warped roater

PNWfrank 23rd May 2009 19:49

+2 for the annual fluid change, brake fluid is hygroscopic and the retained water will decrease the boiling point of the fluid. Boiling brake fluid = spongy brake lever = bad thing
like increased stopping distance.

PNW frank

khaskins 23rd May 2009 20:42

I change mine every year

ted 23rd May 2009 20:50

Dot 5 fluid is silicone based. It is not supposed to suck up moisture. I did a complete change on mine in 1997 and haven't touched it since.

beornj 23rd May 2009 21:50

There's a simple way to check if you should change your brake fluid. Pop a master cylinder cover and see what color the fluid is. DOT 5 turns from purple to a clear amber over time. An indie told me its UV that does that to it, just from the little level check lens. Anyway, he recommended changing it annually or when its not purple anymore.

FoxsterUK 23rd May 2009 22:35

If its DOT 3, 4 or 5.1 then I change it every couple of years or so as it absorbs water and gets spongy. A normal bleed through until it runs clear does the job.

If its DOT 5 then it doesn't absorb water but the water that does get in (by magic?) settles to the bottom of the system and normal bleeding doesn't remove it. However it takes years on a road machine for even a tiny amount to build up so its best left alone.


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