125-200cc How to tell if brake master cylinder seal is a goner

Take the master cylinder off and put your thumb over the hole and see if it pumps, You can get a longer stroke with it off and it may be all it needs to get it working again after its all connected back up - Yes I know it sounds dumb but its worked for me loads of times.

Over which hole? It's pumpin fluid normally n reverse but jus seems it's bypassing piston/caliper.

Wat does the bigger nut under the bleed nipple do? Does that bleed the caliper also?

Edit it's jus the banjo

Right then get a pair of grips if you havnt got a proper hose clamp and clamp the hose as close to the cylinder as possible. Now has it got pedal pressure ? If so you know its not the master and its down the line at the caliper end.

That's wat I'm thinkin. Can't get piston out it's fully recessed. Maybe comp air down inlet hole

Won't this wreck the line bein braided?

YES
Thought it was a stock rubber item

Sounds like a seized piston..put a screw driver so the thing doesn't fly out and pop them out with compressed air.

View: https://www.youtube.com/watch?v=1jp2OCidBV4

Back to work tomoro so hav to wait a coupla weeks to do this.

Visually check inside cylinder tape some very fine sand paper to a drill bit and give it a quick hone, take caliper and master cylinder off bike reverse bleed by clamping piston with g clamp and then bleed as normal with mc lower than caliper and brake line straight make sure the mc is returning fully, still say air in system but trapped in caliper.

Don't ever do this! If you get a stuck piston that all of the sudden lets go you will have broken fingers. Instead place a block of wood to catch the piston. If you don't use a block of wood the piston can come out of there so fast that it will dent an ruin the piston.

Haha yeh il stick a bit of wood or thick plastic in ther

Nah not home from work til wed arvo mate

Cant believe that work takes preference over brakes/bikes down under mate ! Gotta get yer priorities right

It wouldn't if I was single with no kids! Work pays for said bikes n ridin. Jus nd to win lotto is all!

not to hijack but I have been having brake issues with my TE310 as well. rebuilt the master and still having issues. it will build pressure and then the pressure will drop off like a safe. Loosing pressure like that would make me think that I have a leak or a broken line but I cannot find one anywhere. My master cylinder might just be screwed. I looked inside and I didn't really see any major scoring or anything...

if you are not losing fluid (visually from fittings or non visually -slave piston seal) but you are losing pressure for sure its your master. You need to disassemble it again and do a very close inspection of the cylinder. I have had at least one fail. The fail mode is that the hard plating starts to chip, delaminate and flake off the inside walls of the cylinder.....and there is not a seal made that can deal with that. My bet is that is what you have going on. A bright light and even magnifying glass are good inspection tools. Good news is last time I did one it was available. I got mine (Magura) from Factory Pro Supermoto in San Diego they had 10.5 and 9.5 master cylinders I just went with the OEM 9.5mm (it is cast or marked right into the assembly)

http://www.factoryproracing.com/Contact_Us.html

Thanks...yeah that was where I have been leaning towards. I am going to check out the calipers first...pull the piston out and check the square seal.

Worst case, I found a 10mm brembo from this place for about $150 which is about $30 less than if i were to buy it from husky.

http://www.cyclesrus.net/new-brembo-right-side-front-brake-master-cylinder-husqvarna/