Rear master cylinder problems...
 

2012 GasGas EC300R
Nissin Rear Master Cylinder "11" BE660002509

So I need some help here. Right now my rear brakes are completely nonfunctional. I was bleeding the lines to remove air bubbles by depressing the foot lever a few times and cracking open the bleed screw, quickly shutting it and repeating the process. Things were going well when all of a sudden I lost all resistance in the foot lever and now when I depress the lever very little brake fluid is being pushed through the lines even with a wide open bleed screw. There's no external leaking that I can see. Do you think I broke the master cylinder? Or does this sound like it can be repaired with a rebuild kit. If it is a simple rebuild which kits will work for this master cylinder? I can't seem to find much information on a nissin-specific kit. Any advice?

Assuming you have enough fluid in the master cyl,you should be able to build pressure.I always use a vac pump to suck it through fast to minimise the chace of trapped air.Theres also the loop above the master cyl behind the kicker housing that can trap air if not using a vac pump.
If this fails,the piston and cup assembly,(yamaha part# 5un-w0042-50) is the rebuild kit you require if you cant find the GG oem kit.

Thanks for the part number!!

You may wish to use your pushrod,the yamaha one is somewhat shorter to reach for the clevis.

Make sure the piston in the caliper is not stuck. I chased this last year all I needed to do was free the piston by removing the bleeder screw and using an air gun blow in. Piston popped right out.
Had the exact same problems you where having.

Thanks for the part number!!
 

Thanks for the part number!!Thanks for the part number!!Thanks for the part number!!Thanks for the part number!!Thanks for the part number!!Thanks for the part number!!Thanks for the part number!!

Brakes on Newer models
 

Fyi both front and rear master cyl. and calipers are the same as Honda CR's

Sweeping statements should be avoided. My 07 has different calipers to the CRs. As did my 02. Similar for sure, same pads but not bolt on swap. Rear master has different mounts and connection. I think some years CR may have had different bore sizes. Not sure of later model GGs but mates one looks unchanged.

apologize, my title says newer models. meaning 2010 and up . I should have been clear.

Trying not to assume anything, are you holding the pedal down to maintain pressure when you are cracking open the bleeder? Then closing the bleeder before you release the pedal?