Front master cylinder?

[Ar1100s]

Anyone that can help. I have experience with automotive brakes but not much experience with the BMW brakes. I have rebuilt the master cylinder, tried to bleed the brakes per johnnies article with little success.
So I broke it down back to the master cylinder. When pushing on the piston I expected the fluid to squirt out but it doesn't. I'm guessing that either I still have a problem with the cylinder case somehow or it is all part of a closed air tight system and that's why the fluid doesn't squirt out when depresses when I have it off the bike?

[rbm]

There are some very tiny holes between the MC reservoir and the cylinder.  Did you clean debris out of those with a very thin wire during the rebuild?

[Ar1100s]

There is only one hole between the reserve  and the piston chamber. It has been cleaned thoroughly. There also is another hole that had been started but does not go all the way through. Even when I look inside the piston chamber it appears that it has never been bored through. Are these the holes you are talking about!
Thanks for the response.

[rbm]

Your signature says R1100S yet this is a K-bike forum.  Are you inquiring about the MC on your R-bike?  If not, which K-bike (model and year) are you working on? Is it ABS or non-ABS?

[Ar1100s]

I have two. A 1999 r1100s and I found a 1985 k100rt  in someone's yard that was going to get converted to a cafe type bike. It had been sitting in the weather for a couple of years. I got it running, drove through all the gears with a weak rear brake. So now that I know it will run I am starting the improvements. Non abs!

[Inge K.]

There also is another hole that had been started but does not go all the way through.

There always is a second smaller (very small) hole further away from the lever (on all master cylinders)
which must be open to get the master cylinder to function properly.

[Ar1100s]

Inge,
Would you be talking about the hole that leads to the breakline?

[johnny]

greetings ar1100s...

a few photos of whats you gotts will be a tremendous asset to this thread...



j o

[Inge K.]

Inge,
Would you be talking about the hole that leads to the breakline?

No, usually that hole isn't very small  ....compared to the others inside the bore.

In a master cylinder it's always two parallel holes between the reservoir and the bore.
The biggest one ends out between the piston seals when the piston is in the rest position.
The other smallest one ends out in front of the seal that deepest into the bore...when in rest position.

[Laitch]

It's the upper one in this photo from Clymers Manual being discussed, I think, Ar1100s—the hardened sediment polished well enough by the piston to look like part of the bore when you looked into the bore.

[Inge K.]

That's what it normal should look like, and clearly shows the big dimension difference between the ports.

Here is a picture of a 4V reservoir:

[johnny]

greetings inge k...

which one of those hoes squirts brake fluid on your gas tank when you squeeze the lever too fast with the cover off...

j o

[Inge K.]

Good question, Jo.......I don't have the answer, so you must find it yourself.
Next time look veeeeery closely into the reservoir, I would guess the brake fluid won't even reach the tank.

[rbm]

The teeny tiny one JO.

[johnny]

rodger that...

shoulda known...

that teeny tiny hoe pizzez me off...

j o

[Ar1100s]

There it is, partially blocked by the new resevoir. It was crudded  over and looked like part of the piston
housing. I got an old airbrush needle and cleaned it out. I bought a bleeder from HB which saved tons of time and low and behold, I now have front brakes.Gotta buy some new pads!
 Thanks, Inge, Laitch and Johhny!
Great forum!