Brake fluid leak

Thanks Rob,

I bought some DOT4 brake fluid and took the lid off the (good) rear brake fluid container. Turns out the fluid level is so high that I could not see a level in the viewing glass.

I assume that the level in the leaking front brake fluid container is too high as well, but have not checked it yet.

A few questions about what I found:

The brake fluid container lid is held down by two bolts. Once they are removed the metal lid can be lifted up with a bit of prising. Attached to the metal lid is a black rubber seal, which has a "Z" shaped ??expansion?? area that dips into the brake fluid.

On top of the black rubber seal I found a off-white to yellow deposit of small granules of something. I do not know if this is dried out brake fluid or the remnants of some lubricant that was put in there. It looks a bit like small jelly crystals, and on touching them, they turn into an oily film. I'm pretty convinced this is a degradation product of the brake fluid, but confirmation by someone who knows how this stuff works would be reassuring...

There is also some white encrusted deposit around the brake fluid container lid on both brakes (on the outside). I think that might be totally "dried out" brake fluid, while the stuff under the lid and on top of the black rubber seal is half-dried-out brake fluid.

Oh, and general info about brake fluid: How bad is it to get it on your hands and is it very poisonous to the environment (soil / waterways) if you wash spills off with water?

Thanks, Mik

Thanks, Martin.

I wonder if significant water absorption will lead to over-filling of the brake fluid system. I have no idea how much water it can absorb. But if it absorbs 20% water, I suppose it should cause the fluid level to rise a fair bit.

Time to replace the brake fluid and then see if the leak remains.

I assume this is done by opening a bleeder nipple somewhere near the brake pad (maybe with a bit of hose on it?) and then pump the brake lever while pouring new liquid in at the top until it has all been replaced?

How high should the level be after flushing the system? I assume maybe so that the fluid level can just be seen, depending on how the handlebar is turned?

Thanks for everyone's help, Mik

Just to chirp in a bit: The brakes MAY be one of the few NORMAL motorycle components on a VX1. On my Chinese bike this is the case, so I recently had a normal motorcycle shop replace my brake fluid as that is standard procedure for my bike every two years - and the front brake circuit had accumulated either too much air or lost too much brake fluid to allow maximum braking before the lever hit the "throttle" grip (if or if not my participation in a motorcylce safety training session two months ago had any part in this will never be known...).

I would not recommend anyone apart from seasoned automotive of motorcyle mechanics to tinker with brakes on a 240kg/530lb motorcycle! And even those sometimes need a slap on the wrist to do it right. A misunderstanding concerning the brake switch-induced regeneration on my bike and thus slightly more "air" or play in the brake lever travel before the hydraulics kick in led the boss to believe it was normal for the rear brake lever to reach the grip handle WAY before any significant mechanical braking occurred. His mechanics had been very uneasy about this, and they were proven right when I came right back into their shop complaining about this.
A VERY thorough round of refilling some more break fluid (pumped in from the brake calipers, not filled in the brake fluid reservoir at the brake lever!) and pumping the brake lever eventually (after a minumum of 10 minutes of constant pumping!) brought to light air bubbles with the uncompressed volume of half the fluid reservoir volume! Now my rear breake is rock-solid again :-)

And you see that as an argument to not do it yourself??? Sounds like you paid, suffered the risk of driving a bit with non-functional brakes, and ended up doing it yourself in the end!

Thanks Tony!

I spend a few hours working on the brakes today and I am glad that I did not let someone else do it instead.

I can see why people sometimes get poor results from professional repair shops. It's not rocket science, but it takes time and attention (and not the kind of attention that the newest apprentice will be able to muster). Ideally this should be done by two people: One who knows what to do, and the other able to pay attention and do as told without loosing focus for a minute.

My grand plan to flush the brakes without letting air in ended when I heard that slurping sucking noise that the air makes when it gets sucked in through the master cylinder inlet hole....that led to a system full of air and a lengthy process to flush it all out again.
How to avoid that: Have that 2nd person focus on the reservoir and top it up as soon as the level falls to less than 1/2. Or, if working alone, use a plastic hose that is long enough to lift it up to the reservoir level so that the brake fluid stops draining when you lift the hose. What is also important is to use a container with a lid that holds the hose in place, otherwise it tends to flick out and about whenever you tighten the bleeding valve, or just at any time. Messy! An old marmalade jar with a hole punched through the lid will do and make it so much easier.

I used up almost the entire bottle of DOT4 fluid to bleed the front brake and had to re-use some of the fluid (the clean fresh part collected after the old fluid was flushed) because one bottle is not enough to get all the air out. Now it's all good again.

It seems that the rear brake had never been bled properly, because air bubbles started to come out right after I started to drain the old fluid, long before any air would have been sucked into the main reservoir. The rear brake lever had always been a bit spongy, probably due to the difficulties bleeding it properly that you mentioned. I did not have enough DOT4 fluid left to much around for very long to get all air out, but I managed to apply the lessons learned during the front brake service: I topped the reservoir up in time each time, so that no air was sucked in during the flushing. The brakes is strong enough to almost lock the rear wheel on a really grippy dry road, so that's really all I need. I'll try a technique that I read about somewhere today, which supposedly dissolves the air bubbles into the fluid, then lets it leak out through small gaps in between the brake cylinders and pistons. Time will tell if that helps, it's just clamping the brake lever in the fully depressed position to pressurise the system, then leave it overnight.

The closed loop hose sounds like a really good idea for the rear brake. I wonder if removal of the bake and inserting a spacer (instead of the disk) would help to get the air out. The problem is probably the lengthy downward sloping part just before the brake at the rear wheel. If you could lift the brake so that it is the highest point, then the air might come out more easily.

I washed the metal lid and the rubber diaphragm in water, then wire-brushed the metal part clean. Painting it is probably a good idea, maybe next time.

Thanks again, Mik