Brake fluid quality and brands?

Hi,

I've just change my master cylinder from the standard one to a Nissin Radial (courtersy of Northwind, many thanks fitted perfectly).

I've bled it up with DOT4 but there seems to be a fair amount of lever travel, it's fitted with standard calipers and HEL braided lines.

I'm happy there's no air in the system and all the component parts are in good condition and NOT leeking etc.

The only thing I'm left thinking about is the quality of the brake fluid I've used. I work on cars and always use DOT4 brake fluid from my parts supplier in 5L cans, brands vary depending on whats on offer. Obviouslly car braking systems don't have the same level of finess as a bikes.

So my question is do different brands of DOT4 brake fluid have any effect on the braking systems efficiency??

Many thanks

[jambo]

The difference in fluids will only become apparent at high temperature. If the lever action feels poor there is either still a little air in the system, or there is a sticking seal or similar. The fluid is unlikley to be a culprit.

I had this problem with my old cx 500.In the end i had to clamp the pipe pump the lever until i had a good brake lever then release the clamps.It took i while but it was worth it in the end.Hope this helps.

[northwind]

Did you crack the top nipple last? That's a designed-in air trap, bubbles can get caught there instead of going up into the reservoir as they can with an SV m/c (the payoff is that it's easier to make sure there's no bubbles to get trapped). It should have a fair bit of travel, since it's not a massive bore, but it shouldn't have ineffectual travel...

Any old dot 4 should be OK as long as it's not got damp... I generally use the Halfords stuff myself, because it comes in a handily small bottle. Though of late I've used their 5.1 because it's less hygroscopic, means I can take more liberties with it when modding stuff and I get away without changing it as often.

Only problem with 5.1 is that because it isnt hydroscopic any water in the system sinks to the bottom of the system and rests against the piston and causes corrosion. But apart from that its much better!

[northwind]

I think that's just Dot 5, 5.1 is glycol based.

[jambo]

Originally Posted by northwind

I think that's just Dot 5, 5.1 is glycol based.

Correct.

Dot 3, 4, and 5.1 are progressivly "higher" grades of the same type of fluid.

5 is different and for road use I wouldn't bother...

Originally Posted by jambo

Correct.

Dot 3, 4, and 5.1 are progressivly "higher" grades of the same type of fluid.

5 is different and for road use I wouldn't bother...

and 5 isnt compatable with 3,4 and 5.1..it will make your seals swell to the size of a balloon if mixed!!

[jambo]

Originally Posted by SV650Racer

and 5 isnt compatable with 3,4 and 5.1.

Probably should have made that clearer, by "different" I mean wot she said, don't mix 'em.

You can (I believe) mix 3 / 4 / 5.1 provided the lowest rated one is ok for your brake system (so for most bikes that's 4 & 5.1). Generally best to just flush the whole system through with nice new stuff but you don't need to worry about clearing out all your old dot 4 to put in 5.1 for instance.

Originally Posted by mattc

The only thing I'm left thinking about is the quality of the brake fluid I've used.

You can't compress a liquid, so it would never be the brake fluid itself. Over time, the boiling point of the brake fluid is reduced by moisture being absorbed by the brake fluid. This can lead to boiling in the calipers when using the brakes really hard. If this happens, gas is given off by the boiling process and all of a sudden you have no brakes, as you can compress a gas.