On my TRX300FW:
I have had my front brakes completely apart and all lines clean and dried. I fitted a new kit to the master cylinder but I cant get it to pump fluid and I dont get why!!. There is so little to go wrong. The main pumping seal on the pllunger is the right way round, (same as original), the reservoir is full of fluid, so when I push the plunger it should pump. But nothing happens. Is there a trick or what?. I am wondering if something dropped out that I missed. There seems to be nothing in the way of valves or other items, just the main plunger and the return spring/washer.

I am also wondering if the main lid needs to be on the master cylinder, but I presume not.

I have also checked that I have the right kit and seems OK.

Im foxed!!

 

I HAVE HAD THE SAME PROBLEM, SO WHEN CHECKING IT OUT I TOOK THE HOSE OFF OF THE MASTER CYLINDER, I PULL THE LEVER HELD MY FINGER OVER THE HOLE WHERE THE HOSE GOES AND I THINK IT WAS LIKE THE THIRD TIME I DID IT WHEN I PULLED THE LEVER THE FOURTH TIME FLUID WENT FLYING, THIS MIGHT BE THE PROBLEM IT IS AIR LOCKED.

 

From empty they are a pain to bleed. Go to the auto store and get a little bleeder kit. That will make your life easier. It will save you hours.

 

Whenever I rebuild a master cylinder, I bleed it first exactly as atvnatcparts has described. If it won't bleed up and push your finger off the hole, there is something wrong with the master cylinder. A brake bleeder is helpful, but I don't think you absolutely need it. Most times bleeding manually will work fine unless there is another problem, like a clogged brake line, or a stuck slave cylinder on one of the brake panels. Actually, once your master cylinder is bled, often you can open a bleeder valve on the brake panel, and let gravity do most of the work. Make sure you keep the master cylinder full. It may help to make sure your brakes are adjusted before you bleed them. Leave the master cylinder cover off when bleeding.