Which brake fluid?

[sharky]

My ZXR400 trackbike has a spongey front brake lever. What fluid should I use. Also what else could be the cause???

[CB ARGH]

It should usually say which fluid to use around or on the master cylinder. If it's not on there check out the manual, if you've got no manual and one does not exist, DOT4 should do the trick I think.

[Tony.OK]

Dot 4 or 5.1 will be fine..........not DOT 5 though. If your pads are getting low the lever can get spongey, or old brake lines if they aren't braided ones won't help either.

[sharky]

Cheers. It has braided lines and pads have a decent amount of meat on them.

[Pussy]

Try Castrol Response Super DOT4 (in the silver container). I've always had very good results from it

[Sparky Bills]

If its a track bike use a Race brake fluid.
I use Motul 600 brake fluid. Works bloody well!

My mates who race ZXR's also use that fluid and they love it.
Dot 4 etc doesnt have a high enough boiling point for track use. 5.1 would work, but cont go wrong with the race stuff. Doesnt matter what brand.

[cs363]

As you can't really buy crap brake fluid these days and DOT 3 has all but disappeared you can't go too wrong - the main thing is to change your brake fluid reasonably regularly as it is hydroscopic (meaning it absorbs water) the majority of brake fluids are usually a gold or yellow colour when fresh and progressively change colour (darker) the more water they absorb.
The thing to look for is the boiling point, this can vary wildly between brands due to varying formulations etc. the other point here is to look at both dry (as in fresh) and wet (as in water absorbed) boiling points. Obviously a high figure is good on both counts but the better fluids will have a smaller difference between the two giving you a greater safety margin towards the end of their life.

Here are the minimum boiling points for each specification:

Dry Boiling Point Wet Boiling Point
DOT 3 401ºF 284º F
DOT 4 446º F 311º F
DOT 5 500º F 356º F
DOT 5.1 518º F 375º F

Note that DOT 3, 4 and 5.1 are all conventional (Poly Glycol based) brake fluids as described above, however DOT 5 fluid is entirely different as it is Silicone based. The difference here is that silicone based brake fluid will not absorb water. I hear you say, that's the one for me.....err, well no - actually it's not unless you have a brand new brake system, most likely on a pure racing vehicle or similar as the problem with this stuff is it does not mix with conventional fluid and can cause major issues there, but the main problem is that any water that makes its way into your brake system (via poor seals or whatever, make no mistake it does get in) will be trapped under the silicone fluid and will cause localised corrosion which can be extremely dangerous and often costly to fix. There are exceptions to this as some systems are designed purely for silicone fluid, but they are very rare. Consequently it should be changed far more often - typically every race meeting.

Whilst changing the brake fluid is a good place to start, don't think that this is the only possible cause for your spongy brakes. Sticking calipers, master cylinder pistons etc can also contribute and the major contributor particularly on older bikes (over 5 years as a rule of thumb) can be failing rubber hoses. A change to stainless braided hoses will yield a huge improvement in braking power and feel on most vehicles.

Hope that helps. BTW the Castrol fluid that Pussy mentioned is very good value for money and is more than sufficient for the majority of users within a well maintained brake system. It's specs are Dry 536 F and Wet 367 F, so as you can see - well above the minimum for DOT 4 and almsot up to DOT 5.1 spec!
But don't let me stop you buying fancier flash brands

PS. Also check your pad insulators (if fitted as stock) as these can help insulate the caliper from heat transmitted from the pad. Most quality brands of brake pad will usually have an insulating material applied to the back of the pad to assist with this as well as their other reason for being -preventing pad chatter or squeal

[sharky]

Cheers for the info.
I've changed the fluid, the old stuff was bloody filthy. Problem still not solved, I can just about squeeze the lever all the way to the handgrip. I'll look into the other things you guys have mentioned.

[CB ARGH]

Man this thread got me pooing in my knickers thinking I'd put in DOT 5... I can remember saying DOT5 is close to DOT5.1, so it'll do!

Turns out I put in DOT 4, PHEW!

Cheers for the info, real good read.

[cs363]

Cheers for the info.
I've changed the fluid, the old stuff was bloody filthy. Problem still not solved, I can just about squeeze the lever all the way to the handgrip. I'll look into the other things you guys have mentioned.

If the old fluid was bad, it's probably not a bad idea to give it another bleed or two after a bit of use to ensure you have got all the old fluid completely out along with any dislodged sediment etc.

With your problem I would suspect the calipers would be the best place to look, probably find you have one that's got sticking pistons/slide pins or similar - are your brake pads wearing evenly?

[Max Preload]

Try Castrol Response Super DOT4 (in the silver container). I've always had very good results from it

I second that.

...the main thing is to change your brake fluid reasonably regularly as it is hydroscopic (meaning it absorbs water)...

Just a pet peeve of mine but it's HYGROSCOPIC.

[Sparky Bills]

Re bleed them.
If that doesnt fix it, give your calipers a strip/clean (maybe replace seals)
If still not fixed, maybe check the master cylinder seal kit.

Good luck!

[cs363]

Just a pet peeve of mine but it's HYGROSCOPIC.

Yes, you're quite right! My excuse being I didn't have all brain cells fully functioning as a large percentage were bathing in alcohol at the time...

[mouldy]

Tie your brake lever back to the bars when the bikes not being used , this allows microscopic air bubbles to gradually rise up into the master cylinder cos air always wants to go up .

[Shaun]

CASTROL SRF the very best