Brakes-which way does this part go?

[Guest]

Fighting with a master cylinder piston set. Need to know which way this goes together.

The part in question is the little rubber ring seen here.


Does go like this?

Or like this?



The first one seems to let the ridge fit in like this.


While the other way looks like this

[Steve]

Nice, close-up pictures, but I can't tell which way the rod is going to move.

The rubber ring should flare toward the calipers. That way, when you are applying the brakes, the seal will be pushed harder to the bore of the cylinder.

If you turn it around, it will just funnel fluid past the edges.

.

[oldrookie]

In the bottom picture the shaft would move left to right. The brake lever applies pressure to the small end, the fat end pushes against the spring in the far end of the master cylinder.

[old_skool]

The bottom picture then is also installed backwards(picture #3), as Steve said, the cone should be facing the other direction as to push the fluid towards the caliper.

Pic#2 correct

[oldrookie]

Thank you, gents.

I arrived at that conclusion--but not until after I tried it the other way and found it didn't work.

The issue was that I had installed the correct way first and had a leak. Discovered that the seal in question, though installed correctly--as it turned out-- had kinked and lodged a bit of the outer rim down in the part behind it. That caused me to question the work done earlier.

Ever impatient, I had reassembled the MC before Steve's response and then had the joy of knowing that I had to tear it apart again.

Got it together correctly now, with no leaks. Not convinced that the brakes are overly savage, so I am guessing there is air in the system somewhere. Tried all the tried and true bleeding methods, but so far there is no joy in Mudville.

I did ride for awhile this afternoon and it stops without much drama, but I think it required more effort than it did before I rebuilt the system and added the stainless line.

Probably need a second opinion at this point.

[old_skool]

This eve, pump up your brakes, put a ziptie around the handle after the last squeeze, leave it overnite, bleed tomorrow. It's an old trick that's been posted here several times, should work.

[oldrookie]

Did that last night before bleeding it today. Helped...but I think there our more stopping power to be had.

[old_skool]

Either you still have air, or your just dealing with stock mushy lines, which actually do feel better in actual use then at a stop and just squeezing. One of my next areas to improve as well.

[cableguy]

Did you change pads? Perhaps they weren't bedded properly?