Topping brake fluid

I had to top my front brake this weekend, which is now the second time that this happens. In whatever magic way, the fluid disappears from the system. Didn't take any pictures this time, but I have some from the first one. Lesson number one - don't ever work on your scoot in the dark :0

Diagnosis

As the time went, my front brake (or is it still brakes?) got ever more soft, all the way in till I would clamp my finger when braking. Not a good thing. And just as I learned the hard way the skill of keeping my fingers away, I had to push it all the way till it would touch the handle. Even then it would be too spongy to lock the ABS valve. So I prepared to bleed my brakes, though it turned out all that was needed was to add some brake fluid.

Getting there

The braking fluid reservoirs are under the square removable pieces next to the mirrors. Front brake's on the right, and the back brake is on the left.


The plastic screw that holds the cover in place is of the same kind that hold the "windshield". It has tiny thread that screws into and spreads out a plastic socket and therefore locks it in place. Any amount of force pushing the screw in will make the thread slip and the screw will simply stay in place. Also, if the socket is not compressed as it happens when it is all the way in, the screw has nothing to turn on and so will stay in place. To get this thing out, unscrew it with a regular Phillips #2 screwdriver, but try to apply minimum down force. Prying the whole thing out a little bit also helps to lock the screw and give it enough leverage so that it actually comes out.

Once the screw is out, you have to pry open the cover. It has two notches on the sides:


so you have to lift it up at the corner where the screw was and away from those notches to get the lid out. I used a pick and the second time just an Allan wrench stuck through the hole to pry it up a little.

Brake fluid

There are two things one needs to know about brake fluid. It is caustic and it's hygroscopic. Caustic means it will make the metal to rust, the paint to peel off and something in between those two if it gets on your skin or worse yet into thy eyes. This is also one thing that you want to read the label.

Hygroscopic means it will absorb moisture from the air in mad quantities. This is bad because the whole point of using this nasty shit is in that it doesn't boil up to very high temperatures. Water will degrade this property, and if it gets boiling, the vapor bubbles in the system will make the brakes spongy and pretty much useless. What this means is that you shouldn't leave the braking system open for any extended amount of time and same thing goes for the stuff in the bottle that you'll be using. It may also be a good idea to get a new bottle if the old one was lying around unsealed for too long.

Luckily, the stuff is under four bucks in AutoZone. Any automotive DOT3 or DOT4 brake fluid will do.


Topping up

Opening the tank was easy. There are two aluminum screws that hold the lid down. Then there's what looks like a rubber and then a silicone gasket, and both just lift up.



And there it was - an almost empty tank with some rusty stuff in it. Which meant that possible that's the end of the problem. Overfilled with enthusiasm, I poured some brake fluid down - just to overfill it immediately. The damn thing is just really small.


To figure out just how much I overfilled, I pressed down the brake lever. This produced a wonderfully upright stream of brake fluid washing off my forehead. In some sort that was a good thing - getting this into my eye would probably mean a trip to ER. It did mean some very long shower for me and a hose down for the scoot afterwards, though.

So be warned - anything other than slime-near-to-nothing speed when pressing the lever will squirt the fluid out of the tank. Remember the part about it being caustic?

Since I was preparing to bleed the brakes, I bought some clear vinyl tubing beforehand. This turned out extremely useful to get some of the fluid out:


Blocking the other end with my thumb would nicely hold some fluid in the tube that I could transfer to a glass jar.

When I was topping up this weekend, this was the method that I used for filling in. I cut a fresh piece of tubing and then would dip it into the canister, press the other end with my thumb, then transfer the stuff into the tank. Worked great and there was no overfill.

This time I was also way more careful with pressing the lever. I still wanted to do this as the level was next to nothing, so I wanted to see if there's air in the system. There were some bubbles popping up as I pumped it super slow, and after a few times I could see it's just circulating the fluid. Dunno if this was anyhow important tho.

The correct level of the brake fluid is such that it crosses the view window on the side of the tank. Filling to the top will mean your brakes may lock, grind on the disk and overheat, or you simply will not have enough range in the lever to control the effort.

Closing the container is no big deal. Put back the gaskets, close the lid and put in the screws. Both the screws and the tank are aluminum, which means they super easy to thread, so be gentle. Back goes the plastic cover and there it was all ready and working. The brakes come to full power after you've pumped them a few times.

So far it looks like I have to do this every 2000 km.