That boot is just there to keep water and gunk out, and would normally never get in contact with brake fluid or oils...
Just checked as I'm assuming that the P/N 43504MB2006 is also used on the rear brake master and indeed it is: 43504MB2006 bottom comp.
Yes, I can verify that.
Story Time. Are you sitting comfortably ? Then I'll begin..... **
My very first 1100 - way back in September 2000, having given up motocycling in 1982 to enjoy family life - was, shall we say, 'neglected'.
Yes - we shall. Very neglected as it turned out.
I of course was an expert in all things motorcycling in those days. Until I discovered that Japanese bikes work differently. They put the brake pedal and gear lever on the wrong sides for starters. And they used fluid inside the brake cables instead of wire.
But they had these clever rubber devices that kept water out, which I thought was brilliant. So in cleaning up, I helped them with some additional grease inside. Copper grease tends to stay put, so thats what I used.
The next time I took the brakes apart was one of my first ST learning experiences. The rubber boot came detached from the caliper braket and the next 10 minutes was spent trying to find in which part of the garage it had come to rest. Once found, I cleaned it up, applied a new smear of grease and tried to get it back into the groove. No way. Put one side of the lip into the groove, the other side slipped out. Try again. Same again. So I cleaned it all up again so that it wasn't as slippery. No. Still wouldn't go in. The idea is to squeeze the rim through the opening and let it open up again inside the groove - which then held it in place. But it wouldn't do that, as soon as it was squeezed through the opening, it unfurled itself like a coiled spring and ejected itself to a new hiding place on the garage floor.
After about half an hour I had the idea of seeing how large the boot actually was. It was considerably larger than it should have been - I don't know - maybe 20% larger ? Way too ,big. Huge. I eventually got it in place by sticking a thin dowel in the middle and poking each part of the rim into the groove between the dowel and the hole. And that worked - albeit with some creases where the excess rubber had pleated in orded to pretend to be smaller than it actually was.
So I started doing some research and discovered that petroleum based fluids and greases cause nitrile rubber to swell a bit.
A bit ?? 'A bit' is an understatement. It is a lot. And the 'seal' part of it which is supposed to form a waterproof seal around the slider pin, no longer did. It was just a large opening through which the pin slid almost without touching the sides.
I bought new boots all round and a big tin of red rubber grease, which is not petroleum based. And I bought some spares boots. I still have all of the spares. I've not had to touch them since, because petroleum greases and oils do not go anywhere near them. Just the red rubber stuff.
** Probably only recognisable to anyone growing up as a kid in the late 50's in the UK. Listen with Mother.
