Cable Lubrication ?

[jtopiso_imp]

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If you haven’t replaced your clutch and brake fluid after 20k miles you are long overdue.

My VFR800 had over 100,000 miles before I replaced the brake and clutch fluid, and I couldn't tell the difference after the replacement. My 1991 Toyota pick-up, with 200,000+ miles, still has the original brake and clutch fluid.

Sometimes, the seals on the slave cylinder fail if fluid is too old. Sometimes the seals on the master fail too (they live a similar life anyway).

Miatas (mx-5) are known to suffer this issue when fluid has never been replaced.

Replacing brake/clutch fluid is very cheap and usually very easy on most vehicles I have ownd, so...

[Dengie Boy_imp]

I understood that the reason you should change brake/clutch fluid regularly is because it is glycol based (DOT 3 & DOT 4) and therefore hygroscopic ie it absorbs airborne moisture.
Water in the fluid may well change its colour, but more to the point it attacks the slave and master pistons in the system which are usually only chrome plated steel - hence the fuss about upgrading to stainless steel (corrosion free) brake caliper pistons on many classic bike forums. Indeed the water is heavier than the fluid, will eventually work is way down to the lowest point (brake caliper or clutch slave cylinder), corrode the piston that then rip the seals.

Whilst rebuilding a couple of my classics I changed to silicone fluid (DOT 5) that is not hygroscopic and will theoretically last forever (found in Harleys). However, you cannot drain out a system that has once used DOT 4 and then refill it with DOT 5 - they are not compatible.

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[yashko51_imp]

I replace clutch and brake fluid every two years. The hygroscopic effect makes your lever feel a but more spongy though you may not notice it because the change is so gradual. But in am emergency situation, I want my brakes to be as effective as possible
Change the fluid and you should be able to feel a firmer lever-pedal.
And as noted above, any type of water in the lines degrades your components,

[LakeWylieJoe_imp]

Just like changing the oil, you don't do it just so the fluid is pretty. It's to protect the internal parts the fluid comes in contact with. If you let it go too long, you'll get corrosion on the internal parts and the seals will fail at some point (likely at the worst possible time).

When I bought my '86 Nighthawk S used, the fluid was nasty, but the internals were worse. Everything needed rebuilt to make it safe. The brake level went all the way to the bar, even after a flush because there was a ball of old fluid that had turned to jelly and wouldn't come out without removing the pistons from the calipers. The ball of goo compressed when you pulled the lever, so the brakes barely worked.

An ounce of prevention...

[Tev62]

You can get lucky with brake and clutch fluid; my wife's car had the same brake fluid for 12 years and 230K km and it was fine until the day she sold it. But when changing it on a bike is so easy and at only €5 per 500ml it's a no brainer. My Triumph Daytona fluids had not been changed in a while by the previous owner and the rear master cylinder and caliper were wrecked. The cost to fix it back up was a good hit on the wallet and could have been easily avoided, especially as there is no ABS, and a full bleed is a 10-minute job.

[max]

You guys are exactly right, it's the water in the fluid that causes internal corrosion, it gets worse when the bike is not operated for some time and the corrosion can get a hold on some parts, the fluid will still operate as normal though.
Did not know this myself until i took a good look at my cb550 front bake system,i was just in time but it took a long time and many searches on the internet before i realized the tiny hole in the master cylinder had to be carefully opened up to let the air out of the system, allow for expansion of the brake fluid when it gets warm so the brake does not bind up and pressure was restored.

And talk about corrosion; the back of the master cylinders ( where the handle engages the piston under the little rubber boot ) is vulnerable to small fluid leaks which again can corrode mostly the alu parts of the units, i use some persistent lube like grease or heavy gear oil to avert this from happening.

A test showed that an open cup of brake fluid goes bad in one hour, i tested this with a water content tester and was surprised it took such a short time to go bad ( from 0% to more than 3% moisture in 1 hour when left to atmosphere ) i made a video about this test and can post a link if anybody is interested.

[jtopiso_imp]

being dot4 hygroscopic I understand it tends to accumulate moisture, so it will corrode the circuit.

What I don't get is water accumulating on the lower parts of the circuit, even if it weights more. Doesn't water sove into Dot4? Then, after time, the dot4-water mix should be homogenious, and water content be more or less constant along the whole circuit (unless the mix is saturated).

I don't think it's like an oil/water mixture, but an homogenious solution.

Who I'm gonna call? Myth busters?

[Blockhead_imp]

I replace clutch and brake fluid every two years. The hygroscopic effect makes your lever feel a but more spongy though you may not notice it because the change is so gradual. But in am emergency situation, I want my brakes to be as effective as possible
Change the fluid and you should be able to feel a firmer lever-pedal.
And as noted above, any type of water in the lines degrades your components,

Greetings is this your first post on this great forum?

Maybe stop in the New Member section and introduce yourself. Lots of good folks here...welcome aboard!

[dave]

Thanks for all of the great replies gentlemen. You have convinced me that I need to change the fluids in my bike; I'll just add it to my list of things to do - honestly, I will do this ASAP.

[GoldOxide_imp]

Thanks for all of the great replies gentlemen. You have convinced me that I need to change the fluids in my bike; I'll just add it to my list of things to do - honestly, I will do this ASAP.

Now you've given me incentive.

The last time any hydraulic fluid was changed on any of my bikes was, um, ... gee. I am gonna guess 1986?