This needs to be done every two years, so today was for maintenance, not riding.
The GTS was overdue for the brake flush. I decided not to spend half a fortune for a fancy vacuum bleeding tool (MITYvac) that I would need once every two years, but to get the $2.99 One Man Brake Bleeder Kit from HarborFreight. You'll see it in the pictures below. It is a small bottle to collect the flushed fluid and a connector hose to the brake caliper. Details later.
Other MV members have done this with a clear hose and a jar at the end of it, makeshift.
For tools, you will need:
(17mm wrench to remove a wind screen, if you have one installed. It makes access to the next step much easier)
2.5mm hex to remove the brake covers on the headset.
A Phillips screwdriver to open the brake fluid reservoirs
some masking tape
an 8mm wrench for the front and
a 10mm wrench for the rear bleed nipple.
Removing the brake covers. The workshop manual says to also remove the mirrors, which I didn't do and it is not necessary, if you just keep the cover out of the way with a piece of masking tape, as seen in the next picture.
I used this little funnel to not mess up the paint with brake fluid (it is said to be aggressive). In spite of all this precaution, I messed up big time, with brake fluid running down the front fairing and into the right knee pad. Stress! I rushed to wipe it off and it looks like there was no damage. Phew!
This is the culprit. A lousy bottle for dripless pouring. It is best to empty it half way (you won't need more than half), then it is much better to pour from it. They say not to use brake fluid from an opened container, so it doesn't make sense to save it for the next flush in two years ($5 for the bottle, DOT-4 classification)
This shows the bleeding kit, set up for the front wheel. The bottle has a little magnet and I attached it to the brake disc, so it sits as low as possible.
The upper end of the hose goes into a black plastic adapter which then gets squeezed into the bleeding nipple. This part proved to be not well designed, the cone is too coarse, it keeps slipping out and not seal well. I removed it later and pushed the hose directly onto the nipple. Much better!
This is interesting: the pain-in-the-ass instructions I got here on MV require to
1. open nipple (unscrew a bit from hand tight)
2. squeeze brake lever
3. close nipple
4. release brake lever
5. open nipple again
6. squeeze brake lever again,
7. and so on, keeping an eye on the fluid level in the reservoir (never let it get to the bottom, this will induce air into the hose!) and also watching the hose for no more bubbles coming in case you are bleeding the system, or for the new (cleaner?) brake fluid to come out, to tell you that you have flushed the entire system.
For bleeding the system, it will be necessary to do it that way (and a second person will be a great help for this One Man Bleeding Kit), but for just flushing an airless system, I found that gravity will do the job just fine: open the bleeding nipple, watch fluid go through the hose, and keep an eye on the reservoir level. It will go slowly, so you can keep control all by yourself. And no brake lever squeezing necessary!
Close the nipple before the reservoir fluid level reaches the bottom, refill fluid into the reservoir, open the nipple again, repeat this simple pattern until you think you flushed the full system.
This is the amount I let come out (after refilling the reservoir a few times) and I think it was way more than required. One or two refills for the front and maybe one more for the rear system appear to be sufficient. Other opinions are welcome.
It helps if your old fluid is dirty, to see when it was flushed completely. My front system was clear like new, the rear was darker, but still clear.
This is the bottle setup on the rear brake.
This is the final fluid level in the reservoir, before you close it again and be done.
I recommend to test the brake function before you close all the lids and covers. It should feel like or better than before, with a definite resistance before the brake lever can touch the handle bar. It appears that the rear brake will give more than the front, probably due to the longer hose and more chance for the hose to expand a bit under pressure.
Somehow I made a wrong decision when I deliberately introduced air into the system, hoping it would clearly indicate when I had completed a flush. After I was done, the brake lever went all the way to the left handle bar, so I still had air in the system. Now I had to do the above pain-in-the-ass procedure, which I still could have done by myself, reaching both the lever and the nipple, but it was a great help to have Salima do the lever part. After I was sure to have all the air out, the lever felt fine in its travel and I finished up.
A point to watch out for if you do the PITA procedure: there may be brake fluid seeping out from the bottom of the bleeding nipple. If you don't clean this up periodically, it may run down behind the caliper where you can't reach. So, keep an eye on this.
The next time the whole procedure will be easier, and Salima's GTS is due in August.