Bust Rear Master Cylinder, Replace or Fix?

[Guest]

I was out riding the other day when alarmingly my rear brake didn't work anymore. I pulled over to inspect and on a closer look the pedal was going all the way down before actually having any effect. I tried pumping the break to see if this would build any pressure up but still to no avail.

I got home and opened the bike up a bit and the rear brake fluid reservoir was totally empty (levels had only been checked the week previously and was all fine then). I noticed the small rubber boot that sits on the bottom of the MC was torn. Am I right in assuming that this would be the cause of the total drain of brake fluid and the cause of my problem?
Any thoughts on if just replacing the boot would be fine?

Thanks in advance.

[Agemax]

the boot is just a dust and grime protector, not a seal. you should look elsewhere in the brake system for a leak.

[Brendan W]

The boot is probably a dust seal. Replacing it is most unlikely to fix the problem. The inner seals have most likely failed. You could try a get hold of a repair kit and rebuild the m/c. Results can be variable as a lot depends on the condition of the old unit, how much experience you have and how lucky you are.
Any chance of some pictures ?

[tkent02]

The boot is just a dust or moisture boot, it shouldn't leak even without it, should be more or less dry in there. Refill it and watch it to see what happens, it could be leaking from the caliper or from a line someplace.