On Friday, April 16, 2021 at 12:19:30 PM UTC-7, Ralph Barone wrote:
Tosspot wrote:
On 16/04/2021 03:26, Ralph Barone wrote:
sms wrote:
On 4/15/2021 11:13 AM, Tosspot wrote:

snip

Let me get this straight. Shimano have just patented a t-junction?

No. Shimano has patented a t-junction with a built in backflow preventer
valve.

Ok, you are correct, but what does it actually do over a t-junction if
the system is filled?
I’m not sure, since I don’t have a good idea of EXACTLY how disc brake
levers work, but I imagine that when the lever is fully in the off
position, that the reservoir is open to the brake line, so that pad wear
can be accommodated. If this is the case, then applying the brakes via an
auxiliary lever could force brake fluid back up into the reservoir instead
of down into the master cylinder.
Patents that would never hold up in court get issued all the time.
Shimano has the financial resources to fight someone else that uses a
hydraulic tee-junction for bicycle brakes, whether or not the patent
would eventually be upheld.

I once asked one of the attorneys at a semiconductor company that I
worked at why we were not defending a patent that several foreign
companies were openly violating. It was explained to me that if we went
to court and lost then all the companies that were paying us licensing
fees would stop paying and that it wasn't clear if our patent was
defensible.
As you pull the brake lever it pumps fluid down into the actuator. As the pads wear progressively more and more fluid stays down in the actuator. Perhaps you remember that your power brakes had a rather large reservoir that was designed so that it automatically filled the brake reservoir so that the brakes didn't get further and further down the pump until the pedals hit the floor.

This same thing is suppose to happen with hydraulic levers but the reservoir is nearly non-existent and with pad wear the levers pull further and further in. But when you replace the pads you shove the pistons back into the actuator and everything is back to normal. Unless you've allowed the pads to wear so far that they allowed the pistons to come out of the actuator in which case it dumps all of the fluid out of the system and it has to be cleaned, refilled and bled. There are many reasons to not like disks and that is one of them.