Hi Michael,
My guess would be that the master cylinder seal is starting to fail.
You will probably find that if you press VERY gently on the pedal it will
ever so slowly go to the floor as fluid bypasses the seal.
If you stomp on the pedal it will work normally.
What happens in these cases is that the fluid pressure on the downside of
the seal presses the seal lip in and makes it seal against the piston, if
you apply pressure very slowly the pressure does not build up in the system
quickly enough to press the seal lip in to the piston and the fluid flows
past the seal and back to the reservoir.
--
Michael Salter
Check My Blog
http://www.netbug.net/blogmichael/
On Mon, Apr 30, 2012 at 7:17 AM, Michael Oritt <michael.oritt at
gmail.com>wrote:
> Yesterday while returning from a ride in the 100 I applied the brakes and
> the pedal went to the floor--fortunately the emergency brake slowed me down
> enough that I could negotiate the upcoming turn and come to a stop.
>
> After a few deep breaths I stepped on the brake pedal--this time it was
> normal and the brakes functioned seemingly fine. I checked the hydraulic
> fluid reservoir and it was full. I was less than a mile from the garage so
> returned slowly though the brakes continued to work fine and got me back.
>
> In the garage I applied the brakes a few more times, all normal except for
> one time when I held my foot on the pedal it and it went slowly to the
> floor like I was pushing fluid out somewhere through a very small leak but
> there were no leaks. Next push the brake pedal was high and firm. Retested
> several times at 15 to 30 minute intervals--no problems, but obviously
> something is wrong here!
>
> I haven't pulled the master cylinder off and apart yet but am thinking that
> the return valve is somehow hanging up. FWIW I have a BT7 discs in front
> and drums in back and a single circuit setup with a valve in the rear brake
> line which serves as a poor man's proportional setup.
>
> Thoughts?
>
> Best--Michael Oritt
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