Front brakes master cylinder leak

So I had to top my (front) brakes twice so far. If finally appeared to me that there's brake fluid sipping slowly from under the handlebar cover. This was going rather slowly but hey these are the brakes and I wanted to prepare the scoot for the winter. So I just had to dig in there. I am now at 4240 km.



The crack was smashed by some morons when parked at a lake, and the liquid is the brake fluid. No I didn't taste it. But it does have a special feeling to it. Just rub some between fingers, then call 911 in panic.

First I took off front handlebar cover. This is now a separate post since this seems to be quite a repeating procedure :(

It looked as though the fluid is leaking from right under the master cylinder somewhere around the place where brake lever pushes it in. So I took on disassembling the thing.

First I removed the brakes button. It is attached with a tiny screw and a full shebang of plain and split lock washers. It also fits into the brake fluid tank with a small pin but that is not fastened to anything:



Taking off the lever only takes undoing one bolt:



It is M6 so it fits 10mm sockets and wrenches.



The nut has wings in the thread that cut into the bolt. This is apparently a version of a stop nut, but it will not survive being tightened too many times.

Once the lever is off, I could simply slide off a rubber gasket that protects the piston from dust and whatnot. Mine was super badly cracked from what life had for it. This is also similar to other rubber pieces that I discovered are quite cracked. Perhaps they weren't stored right before assembly.



Picture doesn't do it much justice, that thing pretty much fell apart. I now feel attached to it.

Behind the gasket was a retaining ring holding the piston in place. Or so it seemed it should be doing, but it certainly didn't as the ring had jumped off it's socket. Or maybe it never was in place. This seems to have been my only problem.

Once I got the washer out, the whole piston came out.



The thing is surprisingly long



and full of grime, too.

Didn't have my ruler handy, so in case I have to replace it, I took this picture. Apparently they cut them out of pennies, which would explain the quality. Also, appreciate my close photography skill.



This is to show where the ring fits on the piston. The front groove is for the rubber gasket.



It seemed that all I had to do was to fit the ring back in. There's a small groove on the inside of the tank where the ring fits to hold the cylinder in place. The problem was it is just damn too far from the front of this channel, and I just couldn't find retaining ring pliers with pins long enough. Neither would it reach from the side. I replaced those with something makeshift, but the long pins just weren't sturdy enough to bend the the ring.

The whole project took over a week, scoot parked dead with a rubber stopper firm in the brake fluid tank. Which was a crime in progress as these were the last good weather days we've had this season.

I ended up cutting my own pieces for my Channellock retaining ring pliers. It's advantage is in that it has interchangeable pieces that are held in place by a simple stop screw. The pieces themselves are quite apparently made of something suspiciously reminiscent of 3/32" Allen wrenches. At least they are hexagonal and the right size.

I got a few 3/32" hex keys from Ace Hardware for refreshing quarter a piece. Cut the bent part, and ground the other end on a tool sharpening disk. Well, I guess this is a tool, isn't it :) A touch of dremel would have probably worked fine, too. Just rotate the key to grind it down evenly.



This was enough to get the ring just next to thew groove. I had to take the throttle rocker off to get better access. There's a single nut holding the sleeve together and tightening it to the handlebar, right where the cable comes in. Loosen the nut and the throttle slides off. In fact, mine was pretty loose. Messing with the throttle will be like another post.

To get the ring in place, I just slid in a long flat screwdriver and gave it a few blows around the piston. And in it went!



Now that I think about it, a piece of pipe fitting around the piston may have done the whole job, if only the ring wouldn't get stuck dead in the channel (it is covered has a kind of very small groves on it, almost like for extra friction).

Well, that was it, the brakes worked in fact. Added extra fluid and bubbled it with the piston like I wrote in topping the brake fluid post.

I was all ready for that last Sunday ride of the season, and hey I didn't break anything in the process. To finalize such an awesome event, I decided to flush the fluid completely. In fact, you are supposed to change the brake fluid once a year or so as it seeps up moisture, and the winter was around the corner. To make the long story short, I managed to drain it through the bleed screw on the caliper, top it up and bubble it from the tank. This wasn't the whole deal as one is supposed to bleed the brakes when changing the brake fluid. And in that process I threaded the bleeding screw. Sure enough, screw is done of harder metal.

So to hell with the ride, I am stuck next week looking for and replacing the front brake caliper. Which is like, another post.

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.