what master cylinder piston size for 40mm ATEs?

[Major Softie]

If you do replace it, I wouldn't go bigger than 14 myself, but get this one working right before you make the decision.

[DucatiPete]

" , just get it bled then try it out before you change"

Will do!

Thanks

[SteveD]

Pete, any time I've had the system apart and added something new, like ss lines, or new pistons or a new reservoir and 13mm master cylinder, the initial bleed has always been difficult. Easy to do the bleed but despite bleeding thru half a bottle of fluid it took longer to achieve adequate lever action.

That's why I like the retrograde filling of the system 'cause it worked beautifully the first time, despite multiple goes using the usual method. Tying the lever overnight can also help.

There's always https://www.speedbleeder.com too!

[Bob Bennett]

+1 Steve
More than half a bottle for me Pete, normally 2 or 3 days,
Stick with it mate.

[Roy Gavin]

I have an 11 mm MC with twin 40 mm ATEs, and it has a short pull , rock solid , but a little wooden - could probably do with a 10 mm MC.

The 11 mm MC comes from a Guzzi , where it powered two twin piston 48 mm Brembos, without any problems.

Your problem could be a mismatched brake lever, some had a longer nose on them and are actually compressing the cylinder before they move - it is possible to drill and tap a 3mm screw to the end of the short nosed ones as a temp bodge.

I like the Speed bleeder nipples - I push the caliper pistons full back to get the air/ old fluid out of them then pump all the old fluid out through the speed bleeder, and this has worked perfectly every time for me.

[tagordon]

Tie the lever back and leave a few hours. It will work if the mc is ok.

[George Ryals]

If there is air in the system, how does the air get out of the system when the system is sealed from the m/c by the m/c piston being held in with the lever tied down?

[Jean]

Reply to George R.
I wondered THAT too, but after trying to bleed the R80/2 for a couple of days and getting nowhere, I did the tied-lever thing overnight and it worked.
Bumblebees can't fly either.

[tagordon]

Reply#2 to George R.
The mc is closed, or sealed as you described. But it is not at a state of vacuum. So it has its own little atmosphere.
The pressure created by keeping the lever in is what makes it work.
Over a bit of time,with help from the pressure created with the lever being in, the small bubbles that are causing the prob merge into larger bubbles or one big bubble. The bigger bubble(s) will seek the highest point possible. When the lever is released the air goes to the mc reseviour and floats to the top.
I was skeptical myself, untill I watched it work more than once. I even watched carefully and saw the air bubbles in the mc.

[Jean]

Tagordon, that does make sense.
But what about the bees?