I’ve just bought a 2nd hand set of the above brakes, and seem to have a leak from the master cylinder piston. When applying the brake with the lever removed from the bike, fluid leaks from a small hole in the part of the master cylinder that faces the bars.

I’ve tried to bleed the brake, but when applying suction to bleed the master cylinder, air is drawn in through the same small hole from which the fluid leaks.

Has anyone had this before, and can anyone advise on whether this is likely to be a faulty o-ring, or whether the master cylinder itself might be cracked?

Cheers

Are you sure it’s not water that’s in there? Is it definitely brake fluid?.

The wee holes in the back are the breathers for the diaphragm- so it’s not neccesarily a fault at all, if there’s fluid in there it can act exactly like that and it’s pretty common to have some rainwater in there (it’ll smell like brake fluid even if it’s just water, incidentally)

If they’re working, don’t worry about it. If they’re not working- it’ll normally manifest as being able to bleed them, but then inconsistent performance afterwards- then you might have some success removing the diaphragm, cleaning and refitting but failing that if they’re MY2011 to 2013 this is probably the part you need.

http://www.tweekscycles.com/Product.do?method=view&n=3421&p=415119&c=215&utm_source=Google&utm_medium=Base&utm_campaign=Disc%20Brake%20Spares&gclid=CJ-Y3-73mbwCFSQcwwodnUwAFA

Just unscrews with circlip pliars . MY2011 used a slightly different, bulkier design which seems a wee bit more delicate, they changed it midrun. It’s possible though that it’s another fault, cracked m/c would be rare but not impossible.

Mind you it is equally possible that there’s some other completely unconnected issue 😉

Never checked a drawing or anything before, just always assumed it was a breather. When pulling the lever or even when pumping the syringe during bleed, I’ve quite often noticed wee bubbles of liquid coming from there. As northy says, it’s only an issue if the brakes aren’t performing.

As above, there is a very high probability that there is nothing wrong with your brakes, other than that they have got water behind them. I’d try keeping the bike in a nice warm house for a while, before testing them again.

Awesome brake btw. Love mine.

Cheers for the responses guys. They definitely are awesome brakes, these are my second set after having flawless performance of the old style The Ones for nearly 4 years. Finally got sick of making do with Mono M4s on my hardtail, and got a good deal on the new style The Ones.

I hear what you’re all saying about the breather hole, but not sure this explains why air is being drawn in through the breather when you apply suction to the syringe? I’ve now bled the front brake without issue, and didn’t get air being drawn in. I’ll try and re-bleed the rear and see how I get on.

It will do, think about it, when you pull suction on the syringe, the diaphragm is contracting, and so will pull air into the chamber.

Edit – wholeheartedly agree, not just great brakes, but exceptionally reliable and easy to work on. The Italians must have got someone else to make them.

If the diaphragm contracting allowed air to enter during bleeding, then how would you remove all the air from the master cylinder? Strange that this only happened on the rear brake and not the front.

Nobeerinthefridge – Member

The Italians must have got someone else to make them.

I don’t know if this is true but I read somewhere that Formula invented and patented the taperbore technology, discovered it sucks balls, then sold it to Avid basically out of spite 😆

It doesn’t allow air to enter the hydraulic system, as that’s a an enclosed system. It allows air to enter the lever chamber. The diaphragm contracts into the hydraulic side, pulling in air through the breather into the void left behind.

Sounds like the diaphragm assembly is shot, had the same on Loco’s set when bleeding them. Not a really common fault, but it does sometimes happen.

I don’t know if this is true but I read somewhere that Formula invented and patented the taperbore technology, discovered it sucks balls, then sold it to Avid basically out of spite

Lol!

I spoke to half a dozen folks who had brake problems at the puffer last weekend. One thing in common. Can you guess NW?! 😀

I am not getting into Avid slagging, PS Elixir R SLs for sale, they’re ace.

Who said they were avids?

😀

Hmmmmmm. Oh go on then.

They were, erm.

Avids.