Get out the rubber band. …or a clamp. Or duct tape… Even the ever-universal cure Vice-Grips will work.
Thanks to Richard, over on ElMoto.net, I saw this cure for mushy brakes. Clamp the lever tight to the grip… and wait. Overnight is good.
I had the same problem Richard described. When I got the VF500F for my conversion the front brakes were mushy. Once the bike was roadworthy, it was one of the first things on the list to fix, and I got out the trusty vacuum brake bleeding kit. No dice. I did the same thing Richard did, even trying the old-school pump-clamp-bleed-release thing. I even took all the lines apart so I could fill it from zero… still mush. Since it was only one item on the punchlist and the brakes did work, just not really well, I moved on.
(Favorite comment by client when we were photographing an art collection, and hit a piece that was, well, a challenge. “Let’s pay our respects, and move on…” The client? Paul Matisse, grandson of Henri…)
So, I went out to the garage, turned the bars so the master cylinder was highest, and clamped the lever down. This morning I went out to check it. Rock solid brakes.
Why does it work? Air in the brake lines compresses, fluid does not. When you pump the brakes, you can actually break up the air bubbles, sort of atomizing it, actually, and it makes it almost impossible to clear out without replacing all the fluid in the system. The problem is that, in the system, there are nooks and crannies that will resist being replaced with a conventional bleeding. My suspicion is that in the caliper itself there was a pocket, and as soon as you hit the brakes the caliper started atomizing the air. My solution was to rebuild the caliper and replace the pads- something it doesn’t really need, but easy enough to do once you pull everything apart.
When you have the lever pulled, the whole system is open, from the caliper up to the master cylinder, and if there’s no action in the system, air can do what it does- slowly rise to the top of the system. Once it gets to the master cylinder it can escape, the same way the cylinder feeds the system with fluid- through the valve which is now open. It takes a while for air bubbles to migrate through brake fluid in the closed system… but they do.
Thanks Richard, and once again, ElMoto rocks!